Synthesis and conformational analysis of sterically congested (4r)-(-)-1-(2,4,6-trimethylbenzenesulfonyl)-3-n-butyryl-4-tert-butyl-2-imidazolidinone: X-ray crystallography and semiempirical calculations.
The energy based conformational searching technique is a considerable computational request and is still an active area of research. When the property of interest is energy, the following methodology is indicated: full conformational search using molecular mechanics, followed by geometry optimization using semiempirical model for selected conformers, and finally single-point calculation using ab initio models for selected conformers . On the other hand, steric bulkiness of chiral 2-imidazolidinones  plays an effective role in greatly enhancing stereoselectivity, and so sterically congested chiral 2-imidazolidinones [3-5] represent promising auxiliaries for providing excellent diastereocontrol. We reported the synthesis and chiral application of 4-tertbutyl-2-imidazolidinone which were greatly enhanced by the occurrence of N-arylsulfonyl fragments . Moreover, several 2-imidazolidinone derivatives containing diarylsulfonylurea pharmacophore have been synthesized and screened for antitumor activity against various human solid tumors [6-17]. More interestingly the structure of the arylsulfonyl-2-imidazolidinone such as 4-benzamido-3-methyl-1-tosyl-2-imidazolidinone and (S)-(+)-1-[1-(4-aminobenzoyl) indoline-5sulfonyl]-4-phenyl-4,5-dihydroimidazol-2-one has elucidated using X-ray analysis [18,19]. Recently, we reported about the X-ray analysis and computational studies of trans-1acetyl-4,5-di-tert-butyl-2-imidazolidinone in which the crystal unit cell showed two independent molecules connected together by two intermolecular hydrogen bonds .
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In such a way and in continuation of our previous report  we studied single-crystal X-ray and the theoretical conformational analysis of (4R)-(-)-1-(2,4,6-trimethylbenzenesulfonyl)-3-butyryl-4-tert-butyl-2-imidazolidinone (3), as a cyclic arylsulfonylurea, focusing on the configuration of substituents around the 2-imidazolidinone core and to establish the factors that influence this configuration and if this configuration can be predicted for new substituted 2-imidazolidinone.
2.1. Procedure for Synthesis of (4R)-(-)-1-(2,4,6-Trimethylbenzenesulfonyl)-3-n-butyryl-4-tert-butyl-2-imidazolidinone (3). n-Butyl lithium (1.5 M in hexane, 0.5 mmoL) was added to a stirred solution of compound 2 (0.5mmoL) in THF (10 mL) at -78[degrees]C under nitrogen atmosphere for 10 min and n-butyryl chloride (1.0 mmoL) was added dropwise at -78[degrees]C. The reaction mixture was stirred at room temperature for 1 h and then was quenched by passing through silica gel (EtOAc, 100 mL), evaporated under vacuum, followed by column chromatography on silica gel (EtOAc: hexane) to afford compound 3 in quantitative yield.
Compound (4R)-3 (97%): white crystals, mp 125-127[degrees]C (Hexane), IR (KBr) [v.sub.max]/[cm.sup.-1], 1736, 1701 (CO), 1320, 1175 (S[O.sub.2]); [[[alpha]].sub.D.sup.26] = -12.0[degrees] (c 1.00, CH[Cl.sub.3]); [sup.1]H-NMR (CD[Cl.sub.3], 500 MHz): [delta] 6.99 (s, 2H), 4.42-4.40 (d, 1H, 7 = 8.5 Hz), 3.97-3.96 (d, 1H, J = 8.5 Hz), 3.85-3.81 (t, 1H, 7 = 8.5 Hz), 2.85-2.81 (m, 1H), 2.74-2.67 (m, 1H), 2.65 (s, 6H), 2.31 (s, 3H), 1.66-1.58 (m, 2H), 0.93 (s, 9H), and 0.92-0.88 (t, 3H, 7 = 7.3 Hz).
2.2. X-Ray Data Collection, Structure Solution, and Refinement for (4R)-(-)-1-(2,4,6-Trimethylbenzenesulfonyl)-3 n-butyryl-4-tert-butyl-2-imidazolidinone (3)
2.2.1. Data Collection. (4R)-(-)-1-(2,4,6-Trimethylbenzenesulfonyl)-3-butyryl-4-tert-butyl-2-imidazolidinone (3) (Scheme 1) was prepared according to our previous report [4, 21]. A colorless plate crystal of [C.sub.20][H.sub.30][N.sub.2][O.sub.4]S having approximate dimensions of 0.25 x 0.10 x 0.25 mm was mounted on a glass fiber. All measurements were made on a Rigaku AFC7R diffractometer with graphite monochromated Cu-K[alpha] radiation and a rotating anode generator. Cell constants and orientation matrix for data collection obtained from a least-squares refinement using the setting angles of 25[degrees] carefully centered reflections in the range 59.17[degrees] < 20 < 59.87[degrees] corresponded to a triclinic cell (Table 1).
The data were collected at a temperature of 20 [+ or -] 1[degrees]C using the [omega] - 2[theta] scan technique to a maximum 2[theta] value of 120.1[degrees]. Omega scans of several intense reflections, made prior to data collection, had an average width at half-height of 0.28[degrees] with a take-off angle of 6.0[degrees]. Scans of (1.78 + 0.30 tan [theta])[degrees] were made at a speed of 16.0[degrees]/min (in omega). The weak reflections (I < 10.0[sigma] (7)) were rescanned (maximum of 5 scans) and the counts were accumulated to ensure good counting statistics. Stationary background counts were recorded on each side of the reflection. The ratio of peak counting time to background counting time was 2 : 1. The diameter of the incident beam collimator was 0.5 mm and the crystal to detector distance was 235 mm. The computer-controlled slits were set to 3.0 mm (horizontal) and 3.0 mm (vertical).
2.2.2. Data Reduction. Of the 4942 reflections which were collected, 4649 were unique ([R.sub.int] = 0.059); equivalent reflections were merged. The intensities of three representative reflections were measured after every 150 reflections. The linear absorption coefficient, [mu], for Cu-K[alpha] radiation is 16.0 [cm.sup.-1] and an empirical absorption correction based on azimuthal scans of several reflections was applied which resulted in transmission factors ranging from 0.81 to 1.00. The data were corrected for Lorentz and polarization effects and a correction for secondary extinction were applied (coefficient = 6.35905[e.sup.-06]).
2.2.3. Structure Solution and Refinement. The structure was solved by direct methods  and expanded using Fourier techniques . The nonhydrogen atoms were refined anisotropically and hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement (Least-squares: function minimized: [SIGMA][omega]([absolute value of Fo] - [[absolute value of Fc]].sup.2]), where [omega] = 1/[[sigma].sup.2](Fo) = [[[[sigma].sup.2.sub.c](Fo) + ([p.sup.2]/4)[Fo.sup.2]].sup.1] and [[sigma].sup.2](Fo) = e.s.d. based on counting, p = p-factor) was based on 4409 observed reflections (I > 3.00a (I)) and 729 variable parameters and converged (largest parameter shift was 0.09 times its esd) with unweighted and weighted agreement factors of
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The standard deviation of an observation of unit weight (standard deviation of an observation of unit weight: [square root of [SIGMA][omega]([absolute value of Fo] - [[absolute value of Fc]]).sup.2]/(No - Nv)], where: no. = number of observations and nv = number of variables) was 1.26 and the weighting scheme was based on counting statistics and included a factor (P = 0.080) to down-weight the intense reflections. Plots of [SIGMA][omega][([absolute value of Fo] - [[absolute value of Fc]].sup.2]) versus [absolute value of Fo], reflection order in data collection, sin [theta]/[lambda], and various classes of indices showed no unusual trends. The maximum and minimum peaks on the final difference Fourier map corresponded to 0.15 and -0.20 [e.sup.-]/[[Angstrom].sup.3], respectively.
Neutral atom scattering factors were taken from Cromer and Waber  and anomalous dispersion effects were included in Fcalc ; the values for [DELTA]F' and [DELTA]F" were those of Creagh and McAuley . The values for the mass attenuation coefficients are those of Creagh and McAuley . All calculations were performed using the teXsan  crystallographic software package of Molecular Structure Corporation and crystal data summary is given in Table 1. The selected bond lengths, angles, and torsion angles are given in Tables 2-4 and the molecular structure with the atom-numbering scheme and the packing within the cell lattice are shown in Figures 1 and 3, respectively
2.3. Computational Calculations. All molecular modeling calculations were performed using HyperChem version 8.0.6 , running on "Windows Vista" operating system installed on an Intel core 2 duo PC with a 2.66 GHz processor and 2000 Mb RAM.
2.3.1. Conformational Search. Conformational analyses of isolated molecule 3 (3A, 3B, and 3C) were done in the same way using the procedure which is suggested for conformational flexible compounds when the property of interest is energy . Initial X-ray structures for the molecules 3A, 3B and 3C were used for conformational analysis with HyperChem 8.0 . The MM+  (calculations in vacuum, bond dipole option for electrostatics, and RMS gradient of 0.01kcal/mol) conformational searching in torsional space was performed using the multiconformer method [30, 31]. Each molecule 3A, 3B, and 3C was subjected to a separate conformational search and the most stable conformer was energy minimized using semiempirical MO methods AM1  and PM3  included in MoPAC version 2009  using HyperChem as GUI. Vibration frequencies calculation for each conformer was characterized to be the stable structure (no imaginary frequencies).
3. Results and Discussion
As a result of the potential conformational flexibility of the substituent groups of compound 3, we have used solid state molecular structures (as obtained from single crystal X-ray diffraction analysis) to obtain realistic structure as starting geometries for the quantum chemical calculations. Additionally, the data obtained by X-ray diffraction analysis shed light on some interesting features of its molecular structures. Some structural characteristics of compound 3 are the geometrical parameters around the ring nitrogen atoms such as the relative orientation of the n-butyryl and the 2,4,6-trimethylbenzenesulfonyl groups at N1 and N2 positions. Although, the preferred conformation in the solid phase can be different from the solution structure and in gas phase, the X-ray diffraction data are useful for comparative purposes. Overall, the combination of experimental and computational results can help in understanding the physical and chemical properties of this molecule.
3.1. X-Ray Crystal Structure of (4R)-(-)-1-(2,4,6-Trimethylbenzenesulfonyl)-3-n-butyryl-4-tert-butyl-2-imidazolidinone (3). The molecular solid state structure of 3 and numbering system are indicated in Figure 1. Geometrical parameters for compound 3 are collected in Tables 2-4. In the crystal structure, compound 3 crystallizes in the P1 space group (Table 1) and exists in three independent conformationally different molecules in the unit cell (3A, 3B, and 3C; see Figures 1, 2, and 3). Recently, crystal structures having more than one molecule in the unit cell have aroused interest, since these compounds can help in understanding the interactions responsible for packing as well as to guide the design of technologically useful materials . The three molecules present, certain disorder in the core 2imidazolidinone and the substituents linked to such ring. Thus, there is some ambiguity in the atomic positions of the 2-imidazolidinone skeleton, tert-butyl, n-butyryl, and 2,4,6-trimethylbenzenesulfonyl groups of three molecules: 3A, 3B, and 3C. These disorders are expected due to the conformational flexibility of the tert-butyl, n-butyryl, and 2,4,6-trimethylbenzenesulfonyl moieties. The five-membered imidazolidinone ring assumes distorted envelope conformation (half-chair; LISLOO) which may be related to angle strain (angle strain is calculated as the difference between the internal angle and the ideal [sp.sup.3] angle of 109.5[degrees]) . Atoms system ZN2-C3-C2 of 3A, 3B, and 3C are deviated from ideal [sp.sup.3] angle by 6.2[degrees], 6.8[degrees], and 7.3[degrees], respectively. Similarly <C3-C2-N1 system of 3A, 3B, and 3C deviates by 8.5[degrees], 7.9[degrees], and 7.8[degrees], respectively, from the ideal value [17, 18, 20, 36-41]. The same pattern was observed with angle system <N2-C2-N2. The structures of 3A, 3B, and 3C depicted in Figures 1-3 are those more likely on the basis of standard bond distances and angles [17, 18, 20, 41]. In the three molecules (3A, 3B and 3C), the geometrical parameters of the 2-imidazolidinone ring are quite similar with few distortions (Tables 2-4). The geometries of <C4-N1-C2 and <C4-N1-C1 atoms are almost planar rather than the most stable pyramidal form with bond angles of ca. 120[degrees]-126[degrees] for the three molecules 3A, 3B, and 3C. Similarly the geometries of <S1-N2-C1 and <S1-N2-C3 are also planar with bond angles ca. as 122.1[degrees] (3A), 122.6[degrees] (3B), 121.7[degrees] (3C), 124.5[degrees] (3A and 3B), and 125.4[degrees] (3C), respectively [17, 18, 20, 38-41]. This geometry makes the two nitrogen atoms in each molecule distinguishable from a geometrical point of view. Moreover, the planarity angle <N2-C1-N1-C4 of molecules 3A, 3B, and 3C was deviated from the planar urea form by 23 [degrees]-26[degrees] with ca-154.1[degrees], -150.9[degrees], and -157.1[degrees], respectively [20, 41-44]. It must be indicated that the two nitrogen atoms in each molecules occupy anti-positions relative to the mean plane of the ring system. This anti-position of both nitrogen atoms in each molecule is one of the reasons which make the central ring nonplanar . This distortion leads to trans-geometry of n-butyryl fragment around one nitrogen atom and the sulfonyl moiety of the other nitrogen atom. As expected from the previous results , as a result of electron distribution, flexibility, and steric congestion of the system, the 2-imidazolidinone rings in 3A, 3B, and 3C were nonplanar and adopted distorted envelope conformation (half-chair; LISLOO). A common characteristic molecules 3A, 3B, and 3C is the dihedral angle between ferf-butyl and the 2-imidazolidinone rings, with values of -74.0[degrees] (3A), -67.5[degrees] (3B), and -73.5[degrees] (3C) [20, 4346]. Similarly the dihedral angle between n-butyryl group and the 2-imidazolidinone rings is -9.6.0[degrees] (3A), -6.1[degrees] (3B), and -7.8[degrees] (3C) as expected in order to minimize unfavourable steric interactions between ferf-butyl and n-butyryl moiety. Another common feature of the three molecules is the relative orientation of the n-butyryl. They adopt a fransoid conformation and each n-butyryl group is nearly out of the plane of the corresponding 2-imidazolidinone (dihedral angles 6[degrees]-9[degrees]). A remarkable structural feature of the solid-state structures of molecules 3A, 3B, and 3C is the bond angles, whereas the geometrical distortion is manifested in the smaller <C2-C3-N2 (102.2[degrees]) and <N1C2-C3 (101.0[degrees]) bond angles (Figure 1, Table 3) [20, 38-41]. In addition, the structures of molecules 3A, 3B, and 3C were superimposed in order to reveal the conformational differences of the three molecules (Figure 2). The strategy of overlay fit to match 2-imidazolidinone rings and examines any spatial differences between the atoms of the peripheral fragments. The results show that atoms of the n-butyryl, and 2,4,6-trimethylphenylsulfonyl groups occupy different spatial positions relative to the plane of 2-imidazolidinone ring which may explain the existence of such three molecules in one unit cell.
To conclude, it is found that the solid state conformations of the three molecules of 3 (3A, 3B,and 3C)inthe unit cell are quite similar, showing minor differences in some bond length and bond angle and major differences in some torsion angles at the peripheral substitution. However, and despite the high congestion in the molecular structures of these compounds, they form quiet molecular packing that likely reflects the subtle influence of the diverse intermolecular interactions.
The crystal packing of 3 is indicated in Figure 3. The molecules are arranged in a layer constituted by three molecules of 3A, 3B, and 3C and that are maintained by numbers of CH-O, CH-[pi], and [pi]-[pi] interactions [45-47]. The main structural feature of the packing of 3 is that two molecules are quite parallel to each other and connected by [pi]-[pi] interactions of the two aryl fragments (5.03 [Angstrom]) with coordinates -4.250, -2.462, and -0.875, while the third molecule was arranged in a lateral arrangement and approximately in opposite direction to the other two molecules. Additionally, the intramolecular interactions within each molecules of 3 involve O atom of sulfonyl fragment and hydrogen atoms from the C[H.sub.3] of 2,4,6-trimethylphenyl group (1.902-2.081 [Angstrom]). The main putative interactions CH-O, as inferred by relatively short distances and suitable orientations, are indicated in Figure 3. On the basis of the short distances and the wide angle, the CH-O intermolecular interactions are likely to be quite strong and an important factor to determine the crystal packing; these bonds can be considered as nonclassical hydrogen bonds [45-47] involving CH as H-bond donors. Moreover, the third opposite molecule was showing CH-[pi] interaction of the alkyl part of the butyryl moiety of this molecule and the aromatic fragment of the middle molecule (3.86 [Angstrom]). Similarly the C[H.sub.3] group of the 2,4,6-trimethylbenzenesulfonyl group of the middle molecule interacted with aromatic moiety of the third opposite lateral molecule through CH-[pi] interaction (3.60 [Angstrom]). Finally, it must be indicated that the relative orientation between two parallel molecules of 3 in the crystal packing and the third opposite lateral molecule might indicate, besides steric suitability, a tendency to minimize the polarity of the crystal (compensating the dipole moments of the molecules) .
3.2. Computational Studies. Despite the interesting properties of the 1-arenesulfonyl-2-imidazolidinones, these compounds have been scarcely studied from a computational point of view [ 20,49,50]. Our goal was to compute quantumchemical derived properties that would be useful as starting points for understanding the properties of this type of ring system. Moreover, the other main task of conformational analyses of isolated molecules 3A, 3B, and 3C was to examine the stable conformations and a global energy minimum for each molecule. If there was considerable energy difference between the lowest energy of 3A, 3B, and 3C type of conformer, then we concluded that theoretical calculations predicted one type of geometric molecule. Since, the size and the variety of heteroatoms in the 2-imidazolidinones are considerable, a full semiempirical geometrical optimization is computationally very demanding. This work is simplified, if we use a realistic structure as starting geometry for the MM conformational search and quantum-chemical calculation. Therefore, the structures obtained by X-ray diffraction analysis are suitable to this end. Since compound 3 appears as three independent molecules in the asymmetric unit, the three structures (molecules 3A, 3B, and 3C) were separately submitted to the conformational search using molecular mechanic MM+ and the energy minima conformer together with the highest energy conformer were subjected to full semiempirical AM1 and PM3 geometry optimization (Figures 4 and 5). Each conformer was confirmed as minimum or transition state on the basis of frequency calculation using AM1 results.
3.2.1. Theoretical Calculations. Taking into account our interest in the structural study of 2-imidazolidinone, the choice of computational methods which could reproduce the experimental data with reasonable agreement was relevant. Thus, we analyzed the conformational behaviour of compound 3 using semiempirical AM1 and PM3 quantumchemical calculations. Conformational performance of the 2imidazolidinone 3 was examined by the rotation and orientation in the space of the flexible tert-butyl, n-butyryl and 2,4,6-trimethylbenzenesulfonyl groups. Heat of formation, relative energies and dipole moment are collected in Table 5 and characteristic torsional angles, bond angles, and bond distance are also tabulated to illustrate the final geometries obtained. For such compound 3 the MM and semiempirical calculations led to six minimum energy conformations (Figures 4 and 5) within energy differences less than 8kcal/mol (Table 5). Additionally, the molecular structure of compound 3 was determined byMM+ and semiempirical AM1 and PM3 calculations to assess the accuracy of the theoretical methods used for compound 3. Conformations of the single molecules predicted by AM1, more than MM+ and PM3 methods, were approximately similar to that in the crystal (Figure 4).
The arrangement around the N2-S1 and N1-C4 bonds mainly determines the geometry of the N-substituent groups. Based on the geometrical comparison, these forms can be classified into two groups characterised by the torsion angle <C1-N1-C4-C5 denoted as conformer-A, -B, -C and -D for transoid butyryl fragment and conformer-E and -F for cisoid butyryl fragment (around -23.8[degrees] and 137.9[degrees], resp.). For each group there are two or more possible orientations of the 2,4,6- trimethylbenzenesulfonyl moiety (torsion angle <C1-N2-S1-C12) with a similar energy content. However, the relative energy content of these conformers indicates a strong preference for conformations A-B, while the C-F forms are strongly destabilised. Therefore, it seems that the spatial orientations of the O=S=O of 2,4,6-trimethylbenzenesulfonyl and C=O of n-butyryl group relative to C=O of 2-imidazolidinone ring should be affecting the dipole moment as trans-orientation leads to a decrease of this force and vice versa. The high dipole moment represented by cis orientation probably due to the destabilising through-space interactions of the lone pairs of oxygen atoms yields much greater energy differences such as C-F conformations. In light of these findings, A-B conformations were more preferred compared with C-F conformations which are unfavourable and their participation may be negligible. Therefore, it seems that the orientation of n-butyryl group with 2,4,6-trimethylbenzenesulfonyl moiety exerts a significant effect on the conformational preferences of the compound 3 and this behaviour may be attributed to a combination of steric and electronic factors.
The AM1 method shows that the relative orientation of the aryl group of the most stable conformer-A is practically fixed in an anticonformation relative to position of tertbutyl fragment. These features are in concordance with the behaviour of reported molecules [17, 18]. Moreover, the aryl group can adopt two symmetric and isoenergetic conformations in which the tert-butyl and the aryl groups are syn and anti-positions (torsion angle <C1-N2-S1-C12 about -61.7, 61.7[degrees]). Moreover, the energy content of the three similar conformation of the conformer-A is very close with a slight predominance of the orientation of the 2,4,6-trimethylbenzenesulfonyl group as their interconversion requires a low cost (0.05 kcal/mol).
3.2.2. Comparison of the X-Ray and Calculated Structures. The crystal structure of 3 confirms the approximate behaviour of such compound in the gas phase (theoretical calculations). The good agreement between experimental torsion angles determined for 3 and those calculated for the conformer-A (Table 5) supports the correctness of the calculations. Because the barrier of energy of rotation of the three forms of conformer-A is very low so conformerA was predicted representing all the three molecules of X-ray data. The low Gibbs energies of rotation between all possible transoid rotamers indicate the easy conversion between the three molecules in solution, and the solid state crystal structure was obtained in which it showed the important role of intermolecular interaction in stabilizing the molecules in solid states. The different disposition of the n-butyryl group (torsion angle ZC1-N1-C4-C5 = -6.1- -9.6[degrees] in the solid state and -23.8[degrees] for the more favourable orientation computed using AM1 method) may be ascribed to the packing in the crystal structure. Similarity the different orientation of 2,4,6-trimethylbenzenesulfonyl (torsion angle <C1-N2-S1-C12 = -65.9[degrees] - -75.1[degrees] in the solid state and -61.7[degrees] for the most stable conformer-A may be attributed to CH-O, CH-[pi], and [pi]-[pi] interactions in the crystal packing. Owing to theoretical calculations account for very low energy differences between the three dispositions around the N2-S1 bond, their interconversion can take place easily. It was suggested that the change in the spatial orientation of the 2,4,6-trimethylbenzenesulfonyl group could be facilitated by the intermolecular interaction in the crystal structure. The anti-conformation of 2,4,6-trimethylbenzenesulfonyl adopted in the solid state relative to tert-butyl group would be more favourable for their formation due to the CH-O being sterically more accessible with lower dipole moment. These results confirm the flexibility of the 2,4,6-trimethylbenzenesulfonyl group in these 2-imidazolidinone derivatives and the strong dependence on intermolecular interactions as was previously suggested. Moreover, the great similarity between these conformers is the bond length with only 0.05 [Angstrom] deviation among them. Hence, calculations at the semiempirical levels of the conformational energies of compound 3 indicate that the ideal gas-phase global energy minimum conformation is partially observed in the solid state. Rather, the effects of intermolecular interactions in the crystal structure cause the molecules to adopt higher-energy conformations, which correspond to local minima in the molecular potential energy surface. Finally to probe similarity and differences between the three-dimensional structures of the conformer-A and molecules 3A, 3B, and 3C, molecular superposition has been performed (Figure 6). The strategy of overlay fit to match 2imidazolidinone rings and examines any spatial differences between the atoms of the 4-tert-butyl, n-butyryl, and 2,4,6trimethylbenzenesulfonyl. The results show that atoms of the 4-tert-butyl, butyryl, and arenesulfonyl groups occupy different spatial positions relative to each other as described above.
The crystal structures of (4R)-(-)-1-(2,4,6-trimethylbenzenesulfonyl)-3-n-butyryl-4-tert-butyl-2-imidazolidinone (3) were reported. This compound 3 crystallized in layers formed by crystallographic independent molecules. These crystallographic motifs are the consequence of the interplay of the diverse intermolecular interactions in the crystal packing. The crystal packing showed three molecules of compound 3 were stacked as a result of intermolecular interaction. [ANGSTROM] computational analysis of compound 3 was performed using the MM+ force field and fully optimized with semiempirical [ANGSTROM]M1 and PM3 MO methods. The comparison of experimental versus calculated values for the selected bond lengths and angles of 3 is presented and the relative errors in calculated values are less than 3%. Both the experimental and calculated values agree that compound 3 is a sterically congested molecule. Theoretical conformational analyses have pointed out two factors that determine the conformation of the system under investigation. The first one is intermolecular interaction of the crystal packing, such as CH-O, CH-[pi], and [pi]-[pi] interactions, which stabilises and favours the occurrence of three independent molecules and the second factor is steric hindrance between substituents. The generally reasonable agreement between theoretical and experimental results have confirmed that the method which was applied for the theoretical conformational analysis of 2-imidazolidinone is good and useful for related organic molecules. Therefore, these results must be regarded as approximated and only with qualitative and comparative purposes. Moreover, the small differences between X-ray and calculated structures are consequence of different states of matter. During the theoretical calculation single isolated molecule is considered in vacuum, while many molecules are treated in solid state during X-ray diffraction. However, all the calculated geometric parameters, obtained by three used models (MM+, AM1, and PM3), represent good approximations and they can be applied as groundwork for prediction and exploring the other properties of the conformers.
5. Supporting Information Available
Crystallographic data for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as the Supplementary Publication (no. CCDC 734938). Copies of the data can be obtained, free of charge, through application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +441223 336033 or e-mail: firstname.lastname@example.org.
Conflict of Interests
The author(s) declare(s) that there is no conflict of interests regarding the publication of this paper.
The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding work through the research group Project no. RGP-VPP-163.
 W. J. Hehre, Dealing with Conformationally Flexible Molecules, Practical Strategies for Electronic Structure Calculations, Wavefunction, chapter 6,1995.
 H. Matsunaga, T Ishizuka, and T Kunieda, "Synthetic utility of five-membered heterocycles--chiral functionalization and applications," Tetrahedron, vol. 61, no. 34, pp. 8073-8094, 2005.
 N. Hashimoto, T. Ishizuka, and T. Kunieda, "Highly efficient chiral 2-oxazolidinone auxiliaries derived from methylcyclopentadienes and 2-oxazolone," Tetrahedron Letters, vol. 35, no. 5, pp. 721-724, 1994.
 A. A.-M. Abdel-Aziz, J. Okuno, S. Tanaka, T Ishizuka, H. Matsunaga, and T. Kunieda, "An unusual enhancement of chiral induction by chiral 2-imidazolidinone auxiliaries," Tetrahedron Letters, vol. 41, no. 44, pp. 8533-8537, 2000.
 A. A.-M. Abdel-Aziz, H. Matsunaga, and T Kunieda, "Unusual N-acylation of sterically congested trans-4,5-disubstituted 2-imidazolidinones: remarkably facile C-C bond formation," Tetrahedron Letters, vol. 42, no. 37, pp. 6565-6567, 2001.
 H.-Y. P. Choo, S. Choi, S. H. Jung, H. Y. Koh, and A. N. Pae, "The 3D-QSAR study of antitumor arylsulfonylimidazolidinone derivatives by CoMFA and CoMSIA," Bioorganic & Medicinal Chemistry, vol. 11, no. 21, pp. 4585-4589, 2003.
 S. H. Jung, J. S. Song, H. S. Lee, S. U. Choi, and C. O. Lee, "Synthesis and evaluation of cytotoxic activity of novel arylsulfonylimidazolidinones ," Bioorganic & Medicinal Chemistry Letters, vol. 6, no. 21, pp. 2553-2558, 1996.
 S. H. Jung, J. S. Song, H. S. Lee, S. U. Choi, and C. O. Lee, "Synthesis and evaluation of cytotoxicity of novel arylsulfonylimidazolidinones containing sulfonylurea pharmacophore," Archives of Pharmacal Research, vol. 19, no. 6, pp. 570-580, 1996.
 S. H. Jung and S. J. Kwak, "Planar structural requirement at 4-position of 1-arylsulfonyl-4-phenyl-4,5-dihydro-2-imidazolones for their cytotoxicity," Archives of Pharmacal Research, vol. 20, no. 3, pp. 283-287, 1997
 S. Jung, H. Lee, J. Song et al., "Synthesis and antitumor activity of 4-phenyl-1-arylsulfonyl imidazolidinones," Bioorganic and Medicinal Chemistry Letters, vol. 8, no. 12, pp. 1547-1550, 1998.
 E. Y. Moon, S. K. Seong, S. H. Jung et al., "Antitumor activity of 4-phenyl-1-arylsulfonylimidazolidinone, DW2143," Cancer Letters, vol. 140, no. 1-2, pp. 177-187, 1999.
 E. Y. Moon, H. S. Hwang, C. H. Choi, S. H. Jung, and S. J. Yoon, "Effect of DW2282 on the induction of methemoglobinemia, hypoglycemia or WBC count and hematological changes," Archives of Pharmacal Research, vol. 22, no. 6, pp. 565-570, 1999.
 H. S. Hwang, E. Y. Moon, S. K. Seong et al., "Characterization of the anticancer activity of DW2282, a new anticancer agent," Anticancer Research B, vol. 19, no. 6, pp. 5087-5093, 1999.
 S. H. Jung, S. J. Kwak, N. D. Kim, S. U. Lee, and C. O. Lee, "Stereochemical requirement at 4-position of 4-phenyl-1arylsulfonylimidazolidinones for their cytotoxicities," Archives of Pharmacal Research, vol. 23, no. 1, pp. 35-41, 2000.
 S. H. Lee, K. L. Park, S. U. Choi, C. O. Lee, and S. H. Jung, "Effect of substituents on benzenesulfonyl motif of 4-phenyl1-arylsulfonylimidazolidinones for their cytotoxicity ," Archives of Pharmacal Research, vol. 23, no. 6, pp. 579-584, 2000.
 I. W. Kim and S. H. Jung, "Recognition of the importance of imidazolidinone motif for cytotoxicity of 4-phenyl-1arylsulfonylimidazolidinones using thiadiazolidine-1,1 -dioxide analogs," Archives of Pharmacal Research, vol. 25, no. 4, pp. 421-427, 2002.
 I. Kim, C. Lee, H. Kim, and S. Jung, "Importance of sulfonylimidazolidinone motif of 4-phenyl-1arylsulfonylimidazolidinones for their cytotoxicity: synthesis of 2-benzoyl-4-phenyl[1,2,5]thiazolidine-1,1-dioxides and their cytotoxcity," Archives of Pharmacal Research, vol. 26, no. 1, pp. 9-14, 2003.
 A. Guirado, R. Andreu, B. Martiz, D. Bautista, C. Ramirez de Arellano, and P G. Jones, "The reaction of 4-amino-2-oxazolines with isocyanates and isothiocyanates. Synthesis and X-ray structures of polysubstituted 2-imidazolidinones, 1,3-oxazolidines and 1,3-thiazolidines," Tetrahedron, vol. 62, no. 26, pp. 6172-6181, 2006.
 K.-L. Park, B.-G. Moon, S.-H. Jung, J.-G. Kim, and I.-H. Suh, "Multicentre hydrogen bonds in a 2:1 arylsulfonylimidazolone hydrochloride salt," Acta Crystallographica C, vol. 56, pp. 1247-1250, 2000.
 A. A.-M. Abdel-Aziz, M. A. Al-Omar, A. S. El-Azab, and T. Kunieda, "Conformational preferences of sterically congested 2-imidazolidinone using X-ray analysis and computational studies. Part 1: trans-1-acetyl-4,5-di-tert-butyl-2-imidazolidinone," Journal of Molecular Structure, vol. 969, no. 1-3, pp. 145-154, 2010.
 I. A. Al-Swaidan, A. M. Alanazi, A. S. El-Azab, and A. A. M. Abdel-Aziz, "An alternative route for synthesis of chiral 4substituted 1-arenesulfonyl-2-imidazolidinones: unusual Utility of (4S,5S)- and (4R,5R)-4,5-dimethoxy-2-imidazolidinones and X-ray crystallography," Journal of Chemistry, vol. 2013, Article ID 349519, 5 pages, 2013.
 A. Altomare, M. C. Burla, M. Camalli et al., "SIR92-aprogram for automatic solution of crystal structures by direct methods," Journal of Applied Crystallography, vol. 27, p. 435, 1994.
 P. T. Beurskens, G. Admiraal, G. Beurskens et al., "DIRDIF 94: the DIRDIF-94 program system," Technical Report of the Crystallogtaphy Laboratory, University of Nijmegen, Nijmegen, The Netherlands, 1994.
 D. T. Cromer and J. T. Waber, "International Tables for X-Ray Crystallography, vol. 4, Table 2. 2 A, The Kynoch press, Birmingham, UK, 1974.
 J. A. Ibers and W C. Hamilton, "Dispersion corrections and crystal structure refinements," Acta Crystallographica, vol. 17, pp. 781-782, 1964.
 D. C. Creagh and W. J. McAuley, International Tables for Crystallography, Vol. C, (A.J.C.Wilson, Ed.), Table 22.214.171.124, Kluwer Academic, Boston, Mass, USA, 1992.
 "teXsan: Crystal Structure Analysis Package," Molecular Structure Corporation (1985 & 1992).
 Hypercube, HyperChem: Molecular Modeling System, Release 8.0.6, Hypercube, Gainesville, Fla, USA, 1995-2009.
 S. Profeta Jr. and N. L. Allinger, "Molecular mechanics calculations on aliphatic amines," Journal of the American Chemical Society, vol. 107, no. 7, pp. 1907-1918, 1985.
 M. Lipton and W. C. Still, "The multiple minimum problem in molecular modeling. Tree searching internal coordinate conformational space," Journal of Computational Chemistry, vol. 9, no. 4, pp. 345-355, 1988.
 A. A.-M. Abdel-Aziz, "Novel and versatile methodology for synthesis of cyclic imides and evaluation of their cytotoxic, DNA binding, apoptotic inducing activities and molecular modeling study," European Journal of Medicinal Chemistry, vol. 42, no. 5, pp. 614-626, 2007.
 M. J. S. Dewar, E. G. Zoebisch, E. F. Healey, and J. J. P. Stewart, "Development and use of quantum mechanical molecular models. 76. AM1: a new general purpose quantum mechanical molecular model," Journal of the American Chemical Society, vol. 107, no. 13, pp. 3902-3909, 1985.
 J. J. P. Stewart, "Optimization of parameters for semiempirical methods I. Method," Journal of Computational Chemistry, vol. 10, no. 2, pp. 209-220, 1989.
 J. W. Steed, "Should solid-state molecular packing have to obey the rules of crystallographic symmetry?" Crystal Engineering Communications, vol. 5, pp. 169-179, 2003.
 J. L. Flippen, "The crystal and molecular structures of reaction products from -irradiation of thymine and cytosine: cis-thymine glycol, C5H8N2O4, and trans 1-carbamoylimidazolidone-4,5-diol, C4H7N3O4," Acta Crystallographica B, vol. 29, pp. 1756-1762, 1973.
 H. Ueda, H. Onishi, and T. Nagai, "Structure of paminobenzoic acidi-1,3-dimethyl-2-imidazolidinone (1/1)," Acta Crystallographica C, vol. 42, pp. 462-464, 1986.
 M. Kapon and G. M. Reisner, "Structure of 2-imidazolidinone hemihydrate," Acta Crystallographica C, vol. 45, pp. 780-782, 1989.
 O. M. Peeters, N. M. Blaton, and C. J. De Ranter, "Structure of 1-(5-nitro-1,3-thiazol-2-yl)-2-imidazolidinone (niridazole), C6H6N4O3S," Acta Crystallographica C, vol. 40, pp. 1748-1750, 1984.
 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen, and R. Taylor, "Tables of bond lengths determined by x-ray and neutron diffraction. Part 1. Bond lengths in organic compounds," Journal of the Chemical Society, no. 12, pp. S1-S19, 1987.
 A. Caron, "Redetermination of thermal motion and interatomic distances in urea," Acta Crystallographica B, vol. 25, p. 404, 1969.
 P. Vaughan and J. Donohue, "The structure of urea. Interatomic distances and resonance in urea and related compounds," Acta Crystallographica, vol. 5, pp. 530-535, 1952.
 A. Caron and J. Donohue, "Three-dimensional refinement of urea," Acta Crystallographica, vol. 17, pp. 544-546, 1964.
 Y. Umezawa, S. Tsuboyama, H. Takahashi, J. Uzawa, and M. Nishio, "CH/[pi] interaction in the conformation of organic compounds. A database study," Tetrahedron, vol. 55, no. 33, pp. 10047-10056, 1999.
 U. El-Ayaan, A. A.-M. Abdel-Aziz, and S. Al-Shihry, "Solvatochromism, DNA binding, antitumor activity and molecular modeling study of mixed-ligand copper(II) complexes containing the bulky ligand: bis[N-(p-tolyl)imino]acenaphthene," European Journal of Medicinal Chemistry, vol. 42, no. 11-12, pp. 1325-1333, 2007.
 U. El-Ayaan and A. A.-M. Abdel-Aziz, "Synthesis, antimicrobial activity and molecular modeling of cobalt and nickel complexes containing the bulky ligand: bis[N-(2, 6-diisopropylphenyl)imino] acenaphthene," European Journal of Medicinal Chemistry, vol. 40, no. 12, pp. 1214-1221, 2005.
 G. R. Desiraju, J. A. R. P. Sarma, and T. S. R. Krishna, "Dipoledipole interactions and the inversion motif in the crystal structures of planar chloro aromatics: the unusual packings of 1,2,3-trichlorobenzene and 1,2,3,7,8,9-hexachlorodibenzo-pdioxin," Chemical Physics Letters, vol. 131, no. 1-2, pp. 124-128, 1986.
 J. C. Burley, R. Gilmour, T. J. Prior, and G. M. Day, "Structural diversity in imidazolidinone organocatalysts: a synchrotron and computational study," Acta Crystallographica C, vol. 64, pp. o10-o14, 2008.
 A. G. Santos, S. X. Candeias, C. A. M. Afonso et al., "Rationalising diastereoselection in the dynamic kinetic resolution of [alpha]-haloacyl imidazolidinones: a theoretical approach," Tetrahedron, vol. 57, no. 30, pp. 6607-6614, 2001.
Ibrahim A. Al-Swaidan, (1) Adel S. El-Azab, (1,2) Amer M. Alanazi, (1) and Alaa A.-M. Abdel-Aziz (1,3)
(1) Department of Pharmaceutical Chemistry, College of Pharmacy, KingSaud University, Riyadh 11451, Saudi Arabia
(2) Department of Organic Chemistry, Faculty of Pharmacy, Al-Azhar University, Cairo 11884, Egypt
(3) Department of Medicinal Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura 35516, Egypt
Correspondence should be addressed to Alaa A.-M. Abdel-Aziz; email@example.com
Received 2 October 2013; Revised 4 November 2013; Accepted 7 November 2013; Published 5 January 2014
Academic Editor: Fernanda Carvalho
TABLE 1: Summary of crystal data, intensity data collection, and structure refinement for compound 3 at 20.0[degrees]C. (a) Crystal data Empirical formula [C.sub.20][H.sub.30][N.sub.2] [O.sub.4]S Formula weight 394.53 Crystal color, Habit Colorless, plate Crystal dimensions 0.25 x 0.10 x 0.25 mm Crystal system Triclinic Lattice type Primitive No. of reflections used 25 (59.2-59.9[degrees]) for unit cell Determination (2[theta] range) Omega scan peak width 0.28[degrees] at half-height a = 10.6216(5) [Angstrom] b = 16.532(1) [Angstrom] c = 8.9572(9) [Angstrom] Lattice parameters [alpha] = 91.193(6)[degrees] [beta] = 93.849(6)[degrees] [gamma] = 88.097(4)[degrees] V = 1568.2(2) [[Angstrom].sup.3] Space group P1 (#1) Z value 3 [D.sub.calc] 1.253 g/[cm.sup.3] [F.sub.000] 636.00 [mu] (CuK[alpha]) 15.98 [cm.sup.-1] (b) Intensity measurements Diffractometer Rigaku AFC7R Radiation CuK[alpha] ([lambda] = 1.54178 [Angstrom]) Graphite monochromated Attenuator Ni foil (factor = 8.82) Take-off angle 6.0[degrees] Detector aperture 3.0 mm horizontal 3.0 mm vertical Crystal to detector distance 235 mm Voltage, current 35 kV, 150 mA Temperature 20.0[degrees]C Scan type [omega]-2[theta] Scan rate 16.0[degrees]/min (in w) (up to 5 scans) Scan Width (1.78 + 0.30 tan [theta])[degrees] 2[[theta].sub.max] 120.1[degrees] Total: 4942 No. of reflections measured Unique: 4649 ([R.sub.int] = 0.059) (c) Structure solution and refinement Structure solution Direct methods (SIR92) Refinement Full-matrix least-squares P factor 0.0800 Anomalous dispersion All nonhydrogen atoms No. of observations 4409 (7 > 3.00[sigma](I)) No. of variables 729 Reflection/parameter ratio 6.05 Residuals: R; Rw 0.037; 0.056 Residuals R1 0.037 No. of reflections to calc R1 4409 Goodness of fit indicator 1.26 Max shift/error in final cycle 0.09 Maximum peak in final diff. map 0.15 [e.sup.-]/[[Angstrom].sup.3] Minimum peak in final diff. map -0.20 [e.sup.-]/[[Angstrom].sup.3] TABLE 2: Experimental bond lengths ([Angstrom]). Atom Atom Distance Atom Atom Distance S1A O3A 1.416(3) S1A O4A 1.428(3) S1A N2A 1.671(3) S1A C12A 1.777(4) S1B O3B 1.430(4) S1B O4B 1.421(4) S1B N2B 1.664(3) S1B C12B 1.773(4) S1C O3C 1.416(3) S1C O4C 1.425(3) S1C N2C 1.669(3) S1C C12C 1.768(4) O1A C4A 1.215(5) O1B C4B 1.219(5) O1C C4C 1.210(5) O2A C1A 1.200(4) O2B C1B 1.209(5) O2C C1C 1.203(5) N1A C1A 1.376(5) N1A C2A 1.485(5) N1A C4A 1.408(5) N1B C1B 1.380(5) N1B C2B 1.485(5) N1B C4B 1.401(5) N1C C1C 1.386(5) N1C C2C 1.476(5) N1C C4C 1.413(5) N2A C1A 1.395(5) N2A C3A 1.469(5) N2B C1B 1.386(5) N2B C3B 1.473(5) N2C C1C 1.386(5) N2C C3C 1.486(5) C2A C3A 1.523(5) C2A C8A 1.556(6) C2B C3B 1.531(5) C2B C8B 1.549(5) C2C C3C 1.520(5) C2C C8C 1.550(5) C4A C5A 1.507(6) C4B C5B 1.503(6) C4C C5C 1.486(6) C5A C6A 1.531(6) C5B C6B 1.507(7) C5C C6C 1.516(6) C6A C7A 1.490(8) C6B C7B 1.476(9) C6C C7C 1.492(9) C8A C9A 1.533(7) C8A C10A 1.533(6) C8A C11A 1.502(7) C8B C9B 1.515(7) C8B C10B 1.530(6) C8B C11B 1.508(7) C8C C9C 1.515(8) C8C C10C 1.523(6) C8C C11C 1.532(7) C12A C13A 1.401(5) C12A C17A 1.411(6) C12B C13B 1.412(6) C12B C17B 1.407(6) C12C C13C 1.410(6) C12C C17C 1.403(6) C13A C14A 1.383(6) C13A C18A 1.502(6) C13B C14B 1.408(7) C13B C18B 1.487(7) C13C C14C 1.404(6) C13C C18C 1.502(6) C14A C15A 1.377(6) C14B C15B 1.372(7) C14C C15C 1.355(7) C15A C16A 1.363(6) C15A C19A 1.500(6) C15B C16B 1.376(7) C15B C19B 1.507(8) C15C C16C 1.368(7) C15C C19C 1.503(7) C16A C17A 1.396(6) C16B C17B 1.392(7) C16C C17C 1.404(6) C17A C20A 1.500(6) C17B C20B 1.506(7) C17C C20C 1.506(6) TABLE 3: Experimental bond angles (deg). Atom Atom Atom Angle Atom Atom Atom Angle O3A S1A O4A 118.5(2) O3A S1A N2A 108.4(2) O3A S1A C12A 110.8(2) O4A S1A N2A 102.9(2) O4A S1A C12A 110.6(2) N2A S1A C12A 104.3(2) O3B S1B O4B 117.6(2) O3B S1B N2B 103.7(2) O3B S1B C12B 110.8(2) O4B S1B N2B 108.8(2) O4B S1B C12B 110.5(2) N2B S1B C12B 104.3(2) O3C S1C O4C 118.2(2) O3C S1C N2C 107.7(2) O3C S1C C12C 110.1(2) O4C S1C N2C 103.9(2) O4C S1C C12C 111.2(2) N2C S1C C12C 104.7(2) C1A N1A C2A 111.9(3) C1A N1A C4A 126.2(3) C2A N1A C4A 120.4(3) C1B N1B C2B 111.0(3) C1A N1B C4B 126.4(3) C2B N1B C4B 120.5(3) C1C N1C C2C 111.7(3) C1C N1C C4C 126.4(3) C2C N1C C4C 120.5(3) S1A N2A C1A 122.1(2) S1A N2A C3A 124.5(2) C1A N2A C3A 111.1(3) S1B N2B C1B 122.6(3) S1B N2B C3B 124.5(3) C1B N2B C3B 111.3(3) S1C N2C C1C 121.7(3) S1C N2C C3C 125.4(3) C1C N2C C3C 111.0(3) O2A C1A N1A 128.9(3) O2A C1A N2A 124.4(3) N1A C1A N2A 106.7(3) O2B C1B N1B 127.9(4) O2B C1B N2B 124.7(4) N1B C1B N2B 107.4(3) O2C C1C N1C 128.0(4) O2C C1C N2C 125.4(4) N1C C1C N2C 106.6(3) N1A C2A C3A 101.0(3) N1A C2A C8A 113.5(3) C3A C2A C8A 113.2(3) N1B C2B C3B 101.6(3) N1B C2B C8B 113.8(3) C3B C2B C8B 114.6(3) N1C C2C C3C 101.7(3) N1C C2C C8C 114.6(3) C3C C2C C8C 113.4(3) N2A C3A C2A 103.3(3) N2B C3B C2B 102.7(3) N2C C3C C2C 102.2(3) O1A C4A N1A 119.0(4) O1A C4A C5A 122.7(4) N1A C4A C5A 118.2(3) O1B C4B N1B 119.1(4) O1B C4B C5B 122.4(4) N1B C4B C5B 118.4(3) O1C C4C N1C 118.1(4) O1C C4C C5C 123.5(4) N1C C4C C5C 118.4(3) C4A C5A C6A 111.4(4) C4B C5B C6B 112.3(4) C4C C5C C6C 112.5(4) C5A C6A C7A 111.6(4) C5B C6B C7B 112.3(5) C5C C6C C7C 112.9(4) C2A C8A C9A 110.3(4) C2A C8A C10A 106.3(4) C2A C8A C11A 113.9(3) C9A C8A C10A 108.2(4) C9A C8A C11A 108.0(5) C10A C8A C11A 110.1(4) C2B C8B C9B 110.9(3) C2B C8B C10B 106.3(4) C2B C8B C11B 112.0(3) C9B C8B C10B 109.9(4) C9B C8B C11B 107.9(4) C10B C8B C11B 109.8(4) C2C C8C C9C 110.8(4) C2C C8C C10C 107.4(3) C2C C8C C11C 111.8(3) C9C C8C C10C 108.5(4) C9C C8C C11C 108.6(5) C10C C8C C11C 109.7(4) S1A C12A C13A 118.1(3) S1A C12A C17A 120.4(3) C13A C12A C17A 121.4(4) S1B C12B C13B 120.3(3) S1B C12B C17B 118.3(3) C13B C128 C17B 121.3(4) S1C C12C C13C 118.4(3) S1C C12C C17C 120.7(3) C13C C12C C17C 120.8(4) C12A C13A C14A 117.5(4) C12A C13A C18A 125.7(4) C14A C13A C18A 116.8(4) C12B C13B C14B 117.2(4) C12B C13B C18B 127.2(4) C14B C13B C18B 115.6(4) C12C C13C C14C 117.8(4) C12C C13C C18C 125.2(4) C14C C13C C18C 117.0(4) C13A C14A C15A 122.9(4) C13B C14B C15B 122.4(4) C13C C14C C15C 122.3(4) C14A C15A C16A 118.2(4) C14A C15A C19A 121.1(4) C16A C15A C19A 120.6(4) C14B C15B C16B 118.6(4) C14B C15B C19B 120.2(5) C16B C15B C19B 121.2(5) C14C C15C C16C 118.9(4) C14C C15C C19C 121.5(5) C16C C15C C19C 119.6(4) C15A C16A C17A 123.1(4) C15B C16B C17B 122.8(4) C15C C16C C17C 122.8(4) C12A C17A C16A 116.8(4) C12A C17A C20A 126.3(4) C16A C17A C20A 116.9(4) C12B C17B C16B 117.6(4) C12B C17B C20B 125.4(4) C16B C17B C20B 117.0(4) C12C C17C C16C 117.2(4) C12C C17C C20C 126.7(4) C16C C17C C20C 116.1(4) TABLE 4: Experimental dihedral angles (deg). Atom Atom Atom Atom Angle S1A N2A C1A O2A 20.7(5) S1A N2A C3A C2A 144.3(3) S1A C12A C13A C18A -4.1(5) S1A C12A C17A C20A 5.4(6) S1B N2B C1B N1B -162.1(3) S1B C12B C13B C14B -178.1(3) S1B C12B C17B C16B 177.0(3) S1C N2C C1C O2C 23.1(6) S1C N2C C3C C2C 142.4(3) S1C C12C C13C C18C -5.3(6) S1C C12C C17C C20C 5.8(6) O1A C4A N1A C2A 2.6(6) O1B C4B N1B C1B 170.5(4) O1B C4B C5B C6B -13.6(6) O1C C4C N1C C2C 4.7(6) O2A C1A N1A C2A -167.5(4) O2A C1A N2A C3A -175.7(4) O2B C1B N1B C4B 29.6(6) O2C C1C N1C C2C -170.1(4) O2C C1C N2C C3C -171.9(4) O3A S1A N2A C3A -112.6(3) O3A S1A C12A C17A -10.7(4) O3B S1B N2B C3B 13.6(4) O3B S1B C12B C17B 38.3(3) O3C S1C N2C C3C -120.7(3) O3C S1C C12C C17C -12.7(4) O4A S1A N2A C3A 13.6(4) O4A S1A C12A C17A -144.1(3) O4B S1B N2B C3B -112.4(3) O4B S1B C12B C17B 170.5(3) O4C S1C N2C C3C 5.4(4) O4C S1C C12C C17C -145.6(3) N1A C2A C3A N2A 23.3(4) N1A C2A C8A C10A 171.6(4) N1A C4A C5A C6A 176.7(4) N1B C2B C3B N2B 23.2(4) N1B C2B C8B C10B 176.3(4) N1B C4B C5B C6B 162.9(4) N1C C2C C3C N2C 25.1(4) N1C C2C C8C C10C 170.3(4) N1C C4C C5C C6C -178.1(4) N2A S1A C12A C17A 105.8(3) N2A C1A N1A C4A -154.1(4) N2B S1B C12B C13B 106.4(3) N2B C1B N1B C2B 12.4(4) N2B C3B C2B C8B -99.9(4) N2C S1C C12C C17C 102.9(3) N2C C1C N1C C4C -1571(3) C1A N1A C2A C3A -22.4(4) C1A N1A C4A C5A -9.6(6) C1A N2A C3A C2A -18.8(4) C1B N1B C2B C8B 100.9(4) C1B N2B S1B C12B -65.9(3) C1C N1C C2C C3C -22.5(4) C1C N1C C4C C5C -78(6) C1C N2C C3C C2C -21.9(4) C2B N1B C4B C5B -168.1(3) C3A N2A S1A C12A 129.3(3) C3A C2A C8A C9A 168.9(4) C3A C2A C8A C11A 47.3(5) C3B C2B N1B C4B 141.7(3) C3B C2B C8B C10B -67.5(5) C3C N2C S1C C12C 122.1(3) C3C C2C C8C C9C 168.1(4) C3C C2C C8C C11C 46.9(5) C4A C5A C6A C7A -173.9(4) C4B C5B C6B C7B -173.8(5) C4C C5C C6C C7C -173.4(5) C12A C17A C16A C15A -0.2(6) C12B C17B C16B C15B 1.2(6) C12C C17C C16C C15C -0.9(6) C13A C12A C17A C20A -176.8(4) C13A C14A C15A C19A -175.9(4) C13B C12B C17B C20B 177.4(4) C13B C14B C15B C19B 177.4(5) C13C C12C C17C C20C -177.4(4) C13C C14C C15C C19C -175.2(4) C14A C15A C16A C17A -2.0(6) C14B C15B C16B C17B 1.0(7) C14C C15C C16C C17C -2.4(7) C15A C16A C17A C20A 179.4(4) C15B C16B C17B C20B -178.5(4) C15C C16C C17C C20C 179.5(4) C17A C16A C15A C19A 175.6(4) C17B C16B C15B C19B -178.7(4) C17C C16C C15C C19C 176.5(4) Atom Atom Atom Atom Atom Angle S1A S1A N2A C1A N1A -158.4(2) S1A S1A C12A C13A C14A 174.9(3) S1A S1A C12A C17A C16A -175.1(3) S1A S1B N2B C1B O2B 17.4(5) S1B S1B N2B C3B C2B 148.0(3) S1B S1B C12B C13B C18B 2.7(6) S1B S1B C12B C17B C20B -3.4(5) S1C S1C N2C C1C N1C -156.5(3) S1C S1C C12C C13C C14C 175.0(3) S1C S1C C12C C17C C16C -173.8(3) S1C O1A C4A N1A C1A 167.1(4) O1A O1A C4A C5A C6A 0.1(6) O1B O1B C4B N1B C2B 8.5(5) O1B O1C C4C N1C C1C 170.2(4) O1C O1C C4C C5C C6C 4.0(7) O2A O2A C1A N1A C4A 26.8(6) O2A O2B C1B N1B C2B -167.0(4) O2B O2B C1B N2B C3B -176.3(4) O2C O2C C1C N1C C4C 23.3(6) O2C O3A S1A N2A C1A 48.6(3) O3A O3A S1A C12A C13A 171.4(3) O3A O3B S1B N2B C1B 178.1(3) O3B O3B S1B C12B C13B -142.5(3) O3B O3C S1C N2C C1C 42.0(3) O3C O3C S1C C12C C13C 170.4(3) O3C O4A S1A N2A C1A 174.9(3) O4A O4A S1A C12A C13A 38.0(3) O4A O4B S1B N2B C1B 52.1(4) O4B O4B S1B C12B C13B -10.3(4) O4B O4C S1C N2C C1C 168.2(3) O4C O4C S1C C12C C13C 37.5(4) O4C N1A C1A N2A C3A 5.2(4) N1A N1A C2A C8A C9A 54.5(5) N1A N1A C2A C8A C11A -67.1(5) N1A N1B C1B N2B C3B 4.2(4) N1B N1B C2B C8B C9B 56.9(5) N1B N1B C2B C8B C11B -63.7(5) N1B N1C C1C N2C C3C 8.5(4) N1C N1C C2C C8C C9C 52.0(5) N1C N1C C2C C8C C11C -69.3(5) N1C N2A S1A C12A C13A -72.1(3) N2A N2A C1A N1A C2A 11.6(4) N2A N2A C3A C2A C8A -98.4(4) N2B N2B S1B C12B C17B -72.7(3) N2B N2B C1B N1B C4B -150.9(3) N2B N2C S1C C12C C13C -74.1(3) N2C N2C C1C N1C C2C 9.5(4) N2C N2C C3C C2C C8C -98.5(3) C1A C1A N1A C2A C8A 99.1(4) C1A C1A N2A S1A C12A -69.5(3) C1A C1B N1B C2B C3B -22.8(4) C1B C1B N1B C4B C5B -6.1(6) C1B C1B N2B C3B C2B -18.0(4) C1C C1C N1C C2C C8C 100.3(4) C1C C1C N2C S1C C12C -75.1(3) C1C C2A N1A C4A C5A -174.2(3) C2B C2C N1C C4C C5C -173.4(4) C3A C3A C2A N1A C4A 144.2(3) C3A C3A C2A C8A C10A -74.0(4) C3A C3B N2B S1B C12B 129.6(6) C3B C3B C2B C8B C19B 173.2(4) C3B C3B C2B C8B C11B 52.5(5) C3C C3C C2C N1C C4C 145.0(3) C3C C3C C2C C8C C10C -73.5(4) C3C C4A N1A C2A C8A -94.3(4) C4A C4B N1B C2B C8B -94.7(4) C4B C4C N1C C2C C8C -92.3(4) C4C C12A C13A C14A C15A 0.6(6) C12A C12B C13B C14B C15B 1.3(6) C12B C12C C13C C14C C15C -1.5(6) C12C C13A C12A C17A C16A 2.7(5) C13A C13A C14A C15A C16A 1.8(6) C13A C13B C12B C17B C16B -2.2(5) C13B C13B C14B C15B C16B -2.3(6) C13B C13C C12C C17C C16C 3.0(6) C13C C13C C14C C15C C16C 3.7(7) C13C C14A C13A C12A C17A -3.0(5) C14A C14B C13B C12B C17B 1.0(5) C14B C14C C13C C12C C17C 1.9(6) C14C C15A C14A C13A C18A 179.8(4) C15A C15B C14B C13B C18B -179.4(4) C15B C15C C14C C13C C18C 178.8(4) C15C C17A C12A C13A C18A 178.0(4) C17A C17B C12B C13B C18B -178.2(4) C17B C17C C12C C13C C18C 177.7(4) C17C TABLE 5: Heat of formations, relative energies, dipole moments, and selected geometric parameters for the significant conformations of 3 computed using semiempirical AM1 MO level of theory. Comparative analysis with crystal structure 3 (a). Property (a) Conformer Conformer Conformer A (b,c) B C <C1-N1-C4-C5 -23.8 -24.6 -28.0 (-9.9, -40.8) <C1-N2-S1-C12 -61.7 61.7 -109.1 (-46.2, -68.1) <N2-S1-C12-C13 -81.5 -98.3 -97.7 (-71.8, -75.2) <C3-C2-C8-C10 -65.9 -62.7 -63.9 (-64.9, -55.1) <C1-N1-C2 110.0 109.9 110.1 (110.3,109.5) <C1-N2-C3 108.8 108.7 108.8 (112.4,108.6) N1-C4 1.410 1.410 1.41 (1.39,1.45) N2-S1 1.67 1.67 1.67 (1.68,1.79) S1-C12 1.68 1.68 1.69 (1.80,1.79) Hf (kcal/mol) -135.596 -135.069 -134.115 Er (kcal/mol) 0.000 0.527 1.481 Dipole (Debye) 3.57 4.45 4.90 Property (a) Conformer Conformer Conformer 3A D E F <C1-N1-C4-C5 -24.7 156.4 137.9 -9.6 <C1-N2-S1-C12 136.3 -45.7 -107.7 -69.5 <N2-S1-C12-C13 -81.2 -80.3 83.7 -72.1 <C3-C2-C8-C10 -62.5 -66.8 -59.9 -74.0 <C1-N1-C2 109.9 109.0 110.7 111.9 <C1-N2-C3 108.8 108.7 108.8 111.1 N1-C4 1.41 1.41 1.41 1.408 N2-S1 1.67 1.67 1.66 1.777 S1-C12 1.69 1.67 1.69 1.671 Hf (kcal/mol) -132.739 128.334 127.122 -- Er (kcal/mol) 2.857 7.262 8.474 -- Dipole (Debye) 6.35 5.06 9.01 -- Property (a) X-ray 3C 3B <C1-N1-C4-C5 -6.1 -7.8 <C1-N2-S1-C12 -65.9 -75.1 <N2-S1-C12-C13 -72.7 -73.5 <C3-C2-C8-C10 -67.5 -73.5 <C1-N1-C2 111.0 111.0 <C1-N2-C3 111.3 111.0 N1-C4 1.401 1.413 N2-S1 1.664 1.669 S1-C12 1.773 1.768 Hf (kcal/mol) -- -- Er (kcal/mol) -- -- Dipole (Debye) -- -- (a) All values correspond to fully optimized geometries. (b) Relative energies for the three similar conformations resulted from the separate conformational analysis of 3A, 3B, and 3C around the N1-C4 and N2-S1 bonds: 0.000, 0.110, and 0.05 kcal/mol, respectively. (c) Values in bold, plain, and italic text corresponding to MM+, AM1, and PM3 geometry optimization, respectively.
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|Title Annotation:||Research Article|
|Author:||Swaidan, Ibrahim A. Al-; Azab, Adel S. El-; Alanazi, Amer M.; Abdel-Aziz, Alaa A.-M.|
|Publication:||Journal of Chemistry|
|Date:||Jan 1, 2014|
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