Possibilities of cyclization of side alkyl chains of n-alkylphenols and n-alkylbenzenes in the environment of a stationary phase.
Gas chromatographic measurements of relative retention times ([R.sub.t,rel]) of n-alkylphenols and n-alkylbenzenes [C.sub.7]-[C.sub.12] on capillary columns with both polar and nonpolar stationary phases at temperatures of 125-140 [degrees]C showed that these retention times increase non-linearly with the number of carbon atoms in a molecule (z) (Fig. 1) (Buryan and Macak, 1982). Two linear areas in the consecutive intervals [C.sub.7]-[C.sub.9] and [C.sub.9]-[C.sub.12], with the slopes of each line being different, were proved in the relation log [R.sub.t,rel] = az + b (where a and b are constants), although only one line was expected to be found. The complete dependence was thus of a divergent character with break (Fig. 1). This dependence was under the mentioned conditions also found in the case of n-alkylphenol methylethers (Buryan and Macak, 1982).
In classic considerations on the dependence of retention times on the number of carbons in different homologous series of gas chromatographically separated substances, purely linear dependence without any divergence is always considered, be it for isotherm or non-isotherm separations (Purnell, 1962; Leibnitz and Struppe, 1966; Hartus and Habgood, 1966).
However, the divergence detected in the dependence log [R.sub.t,rel] = az + b suggests, that the behavior of molecules of the compounds in question during separations in stationary phases is more complicated than has been assumed by the classic considerations. The relation log [R.sub.t,rel] = a + bz should be expected to be purely linear as a result of the growing number of carbon atoms in the molecule (Simpson, 1970) and the corresponding increase of [R.sub.t,rel] or more precisely log [R.sub.t,rel] with boiling points ([T.sub.b]) of the given homologs (log [R.sub.t,rel] = a + b[T.sub.b]). The mentioned purely linear relation was frequently applied when identifying unknown substances using data acquired through gas chromatographic separations, but the validity of this usage is questionable.
[FIGURE 1 OMITTED]
In the study (Buryan and Macak, 1982), the relative retention times were expressed as a logarithm of the ratio of the retention time of the given n-alkylphenol substituted in the positions ortho, meta and para and phenol, and in the case of n-alkylbenzenes as a logarithm of the ratio of the retention time of n-alkylbenzene and benzene. The mentioned divergence (break) in the increase of retention characteristics was always observed at [C.sub.9].
In our work, the following possibilities were considered as an explanation of this phenomenon.
* Cyclization. In a high density stationary phase, the longer alkyl side chains of n-alkylphenols and n-alkylbenzenes are subject to cyclization as a result of the resistance force of this phase affecting molecules of the compounds during their thermal and diffusion motion. Consequently, common conventional aromatic-aliphatic molecules become new molecules with quasi-alicyclic parts. It is likely that in comparison with the conventionally conceived molecules, the resulting aromatic-quasi-alicyclic molecules are characterized by rather different, possibly even completely different non-covalent interactions between the molecules (chiefly van der Waals interactions), which then affect the retention characteristics.
* Association. The molecules of the compounds in question are of an aromatic-aliphatic character. Such molecules tend, in a dense environment (e.g. in organic gels), to form molecular aggregates, as was discovered during the research on the formation of coal structures (Straka et al., 2002; Straka, 2003). A similar phenomenon may occur in the environment of a dense stationary phase. The molecules in question may associate, which would lead to a change in retention characteristics. The association could also increase with the growing length of the side alkyl chain and might strongly manifest itself in the case of molecules containing more than 9 carbons.
* Non-covalent interactions with a stationary phase. With the increasing number of carbons in the molecule of n-alkylphenols and n-alkylbenzenes, intermolecular interactions between compounds in question and the stationary phase might change non-linearly with the growing number of carbons in the molecule. These interactions may manifest themselves differently in polar and nonpolar phases.
The mentioned phenomena can be evaluated and compared using methods of computational chemistry. In order to assess cyclization, association and different interactions, energies of covalent bonds and non-covalent interactions (mainly van der Waals) can be computed. For the purpose of this assessment, molecular conformations which are realistic and energetically advantageous or possible and are in correlation with the ascertained chromatographic data can also be estimated.
On the basis of experience with the evaluation of aromatic, aromatic-aliphatic, aromatic-alicyclic and phenolic structures in terms of energy using the methods of molecular and quantum mechanics (Carlson, 1991), two methods of molecular mechanics were selected for the calculations (see below).
The aim of the presented work is to explain the divergence (break) in the logarithmic dependence of relative retention time on the number of carbons in the molecule in the case of n-alkylphenols and n-alkylbenzenes by utilisation of computational methods of molecular mechanics and to clarify the behavior of these compounds in the environment of a stationary phase of a capillary column. Further, to describe a cyclization of side alkyl chains in a stationary phase as a new phenomenon.
For considerations the retention data obtained on a nonpolar stationary phase of Apiezion K and a polar stationary phase of trixylenylphosphate-phosphoric acid (95:5) at temperature of 130 [degrees]C (Buryan and Macak, 1982) were taken into account.
For calculations the molecular mechanics methods were chosen and two force fields, MM+ and AMBER (Becker and Allinger, 1982; Allinger and Yuh, 1982; Howard et al., 1994), were used. The reason is that these methods use an analytical and relatively simple potential energy functions for describing the interactions between a set of atoms, further, they are empirical and accurate and very suitable for small organic molecules. Important is that atom types, not atoms, are the fundamental basis for calculating interactions. In these methods the interaction potential describes both bonding and non-bonding interactions. In the potentials the following energetic terms were calculated:
* bond stretching ([E.sub.bond]), which is associated with deformation of a bond from its standard equilibrium length,
* bond angle bending ([E.sub.angle]), which is associated with the deformation of an angle from its normal value,
* stretch-bend ([E.sub.stretch-bend]); bond stretch and angle bending cross term, which includes coupling between bond stretching and angle bending,
* dihedrals ([E.sub.dihedral]); torsional energy, which is associated with the tendency of dihedral angles to have a certain n-fold symmetry and to have minimum energy,
* van der Waals ([E.sub.vdWaals]), which describes the repulsive forces keeping two non-bonded atoms apart at close range and attractive forces drawing them together at long range,
* electrostatic ([E.sub.elst]), which describes the classical non-bonded electrostatic interactions, particularly dipole-dipole interactions.
These energetic terms were calculated both by MM+ and AMBER methods, except [E.sub.stretch-bend], which was calculated only by means of the MM+.
The mentioned potential energies of covalent bonds and non-covalent interactions were calculated for common (conventional) n-alkylphenols and n-alkylbenzenes and also for models of cyclized forms of these compounds. The conceptions of the cyclized forms were formulated on the basis of the study of distribution of electron densities (atomic charges in a molecule) in common and cyclized molecules. As expected, in n-alkylphenol molecules, a high electron density was detected on the oxygen of the hydroxyl group and a very low electron density on the hydrogens of the terminal methyl group. The closing of the cyclanic ring was thus easily implemented by a hydrogen bridge as shown in Fig. 2 a. The conception of the cyclized form of alkylbenzenes was more complicated. The electron density on the alkyl carbon in the [alpha] position with respect to the benzene ring was discovered to be considerably higher in the case of the cyclized form than on the other carbons and, especially, on hydrogen atoms of the methyl group in an alkyl chain. The closing of the cyclanic ring was thus implemented by an interaction of methyl hydrogen with the ascribed charge +[delta] and the benzene ring with the ascribed charge -[delta] (Fig. 2 b). The basic conceptions of cyclized forms and models of these forms, for the sake of calculations demonstrated on n-propylphenol and n-propylbenzene, are also shown in Figs. 2 c, d, namely for the case of ortho n-propylphenol and alicyclic n-propylbenzene. In the latter case, the cyclization occurs until it reaches the position neighboring the position of a propyl substituent (i.e. n-propylbenzene is cyclized to the position ortho with respect to the propyl). The cyclization here is realized on the terminal methyl group (-C[H.sub.3] cyclization).
[FIGURE 2 OMITTED]
Besides the-C[H.sub.3] case, cyclization was also considered and calculated for the group -C[H.sub.2]-neighboring C[H.sub.3]-(i.e. in the position a with respect to C[H.sub.3]-, Fig. 3, -C[H.sub.2]-[alpha] cyclization) and for the group -C[H.sub.2]-in the position [beta] with respect to the group C[H.sub.3]-(Fig.4,-C[H.sub.2]-[beta] cyclization). These cyclizations were considered for molecules from methyl- up to hexylphenol and from methyl- up to hexylbenzene. With n-alkylphenols and n-alkylbenzenes the cyclization was considered and calculated for the positions ortho, meta and para; the mentioned energy terms were calculated for 252 cases altogether. The calculated energies of covalent bonds and non-covalent interactions for common and model cyclic forms were compared, and it was ascertained that energy changes are related to the determined retention times.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
The program HyperChem also enables to perform measurements of the distances between atoms of defined molecules. This possibility was utilized for the measurement and comparison of the maximum sizes of common and cyclized molecules of the examined compounds. The part of the program, Atomic Charges, was also used for the study of distribution of electron densities in the molecules of the observed compounds.
3. RESULTS AND DISCUSSION
With regard to the temperature of the chromatographic column (125-140 [degrees]C), a possibility of side-chain cyclization was considered first. This possibility was based on the conception that in high-density stationary phase, the longer side alkyl chains of n-alkylphenols and n-alkylbenzenes are subject to deformation as a result of resistance of this phase affecting molecules of these compounds in motion. Conventional aromatic-aliphatic molecules are thus transformed into aromatic-quasi-alicyclic molecules. Cyclization is then accompanied by decrease in the effective size of molecules, which is significant for [C.sub.9] and larger molecules. Aromatic-quasi-alicyclic molecules of a smaller size are more easily mixed with the dense stationary phase, and the formed system is, in comparison with a system with common aromatic-aliphatic molecules, more homogenous and thus thermodynamically more stable. The reduction of the maximum size ([D.sub.max]) of molecules during the cyclization of the side chain is shown in Table 1. The change in size of molecules moving through a chromatographic column is then accompanied by changes in intermolecular interactions and subsequently in change in relative retention time.
Calculation results for the energies of covalent bonds and non-covalent interactions for ortho n-alkylphenols (common, cyclized through C[H.sub.3]-, cyclized as -C[H.sub.2]-[alpha] and -C[H.sub.2]-[beta]) and n-alkylbenzenes both common and cyclized into the position ortho with respect to the substituent (again cyclization through C[H.sub.3]-, as -C[H.sub.2]-[alpha] and -C[H.sub.2]-[beta] are summarized in Tables 2, 3 and 4. From these tables it is evident that cyclization hardly brings any important changes in covalent bonds (only small changes in electrostatic interactions and some expected changes in the [E.sub.angle] term). However, substantial changes in van der Waals interactions between nonbonded atoms inside molecules took place. Changes in van der Waals forces inside the cyclized molecules must also be reflected in changes of these forces between molecules. The dependence of van der Waals forces on the number of carbons (z), demonstrated in Figs. 5 and 6, is of the same (divergent) character as the detected dependence 1 of logarithms of retention times on z (Fig. 1). This finding is in accordance with the fact that the same dependences were detected both in cases of polar and nonpolar phases and also in the cases of alkylphenols and alkylbenzenes, because retention data and their changes are in the given case related with intermolecular forces rather than with the structure of the considered compounds.
The same results have been obtained in the case of ortho, meta and para n-alkylphenols cyclized on the group -C[H.sub.3] and even in the case of n-alkylbenzenes, cyclized on the group -C[H.sub.3] as well to ortho, meta and para positions with respect to the substituent. Another example is shown in Fig. 7. Therefore, attention was focused on systematic calculations of the energies of van der Waals interactions. Numerical values of these energies show strength of van der Waals forces and results are summarized in Tables 5 and 6. From the data in these tables it is evident that in all the cases the divergence in the size of these interactions occurs at z = 9 (to be more specific when phenol or benzene are substituted by n-propyl). However, this result was ascertained only for alkylphenols and alkylbenzenes cyclized on the terminal methyl group. In the case of -C[H.sub.2]-[alpha] and -C[H.sub.2]-[beta] cyclizations, the detected [E.sub.vdWaals] values were similar to common n-alkylphenols and n-alkylbenzenes or no relevant dependences on z were found.
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
An increase in van der Waals interactions inside the cyclized molecules (i.e. intramolecularly) must also be reflected in an increase of forces between molecules (i.e. intermolecularly). More intense effect of attraction forces between molecules should then manifest itself through a corresponding increase of boiling temperatures of the [C.sub.9]-compounds and higher in both types of molecules in question. The increase of intermolecular forces caused by cyclization was confirmed by comparison of boiling points of normal and cyclic hydrocarbons [C.sub.3]-[C.sub.8]. The results are shown in Table 7 (the values of boiling points were taken from the compendium (Spravotschnik Chimika, 1951) and verified against the compendium (Vecera et al., 1975)). From the values shown in Table 7 it is evident that boiling points of cyclic hydrocarbons increase with the number of carbons z in the molecule non-linearly, divergently, similarly to van der Waals forces and, consequently, relative retention times. Due to obvious importance of the dependence of the [T.sub.b] values on z in the case of normal and cyclic hydrocarbons, this dependence is graphically depicted in Fig. 8 as a difference of boiling points ([DELTA][T.sub.b]) of these hydrocarbons in dependence on z.
If a change in the relative retention time as a result of cyclization is caused by a change in the size of the molecule moving in a chromatographic column and a change in both intramolecular and intermolecular van der Waals forces, then the related cyclization of alkyl chain could really be, in the case of n-alkylphenols, accompanied by formation of a hydrogen bridge between the oxygen in the phenolic group -OH and a hydrogen of the terminal group -C[H.sub.3] of the alkyl; in other words, in the case of n-alkylphenols, the tendency to form hydrogen bridges resulting in a heterocyclic ring with six or more members being formed including also one C-C bond of the aromatic ring of phenol as shown in Fig. 2 could actually be considered. Similarly, in the case of alkylbenzenes, a tendency to integrate could exist between the benzene ring (-[delta]) and a hydrogen of the terminal group of the -C[H.sup.3] alkyl (+[delta]), resulting in a formation of a five-membered or more-membered ring, including also one C-C bond of the aromatic ring of benzene (Fig. 2).
[FIGURE 8 OMITTED]
The question of association. The molecules of the compounds in question are of an aromatic-aliphatic character. As already mentioned above, in the environment of a dense stationary phase, molecular aggregates may be formed. The molecules in question can thus associate in the separation zone, which would lead to a change in retention characteristics. It is likely to be that the association would increase with the increasing length of the side n-alkyl chain increasing and would strongly be manifested in the case of molecules with a number of carbons higher than 9. Therefore, the close association was investigated both in the case of n-alkylphenols and n-alkylbenzenyes for the system of two molecules. This was done by calculating the energies of van der Waals interactions ([E.sub.vdWaals]) using the above-mentioned methods after the two common molecules (i.e. without the side chains being cyclized) were conformed until the state of the energy minimum was reached. The calculated energies were then compared with the energies of van der Waals interactions in two non-associated (isolated) molecules. The data summary is in Table 8.
From the data in Table 8 it can be seen that intensive nonbonding physical interactions occur in the association of two molecules of n-alkylphenol or n-alkylbenzene. These interactions can determine the elution/retention behavior of molecules when they are moving through the chromatographic column. However, unlike in the case of cyclized forms no dependence of the [E.sub.vdWaals] values on the length of the n-alkyl chain was detected. Moreover, if we take into consideration that the measurements were taken at temperatures 125-140 [degrees]C, the close association of the molecules is unlikely.
The question of non-covalent interaction with the stationary phase. As has been already suggested, in the case of both the examined n-alkylphenols and n-alkylbenzenes, an increase in the number of carbons in the molecule may be accompanied by a change in the intermolecular interaction between a non-conventional compound and the stationary phase. A consequence of the non-linear changes in these interactions would also be a non-linear progression of retention times. However, these interactions would have to change differently in the case of polar and nonpolar stationary phases, with the dependence of the elution/retention times on the number of carbons consequently being of a completely different character for each type of the phase. Nevertheless, this was not observed. As shown in Fig. 9, the character of the dependences is the same, measured in the case of alkylbenzenes for both the polar and nonpolar phases. It seems that not even non-covalent interactions with the stationary phase are the cause of the observed progression of retention times.
Therefore, it is the cyclized form of the considered compounds that is preferred. The preference for the cyclized form arises also from the fact that cyclanic-aromatic ethers with five- and six-membered cyclanic rings with oxygen and an interconnected aromatic ring (Fig. 2) (which are thermodynamically stable compounds) are formed. (In the case of para methylphenol, higher values of some covalent energies were calculated due to higher strain of bonds, however, no values on principle eliminating a hypothetical cyclization were found).
[FIGURE 9 OMITTED]
From the thermodynamical aspect, it is the affinity of the low-molecular compounds that is important in the given context in question with the stationary high-molecular phase when they are being mixed with this phase. The degree of affinity is the change in Gibbs energy of mixing when the molecules of alkylphenol or alkylbenzene are blended with high-molecular chains of the stationary phase ([DELTA][G.sub.mix]) at constant temperature and pressure:
[DELTA][G.sub.mix] = [DELTA][H.sub.mix] - T [DELTA][S.sub.mix] < 0 (1)
where [DELTA][H.sub.mix] is the enthalpy of mixing, [DELTA][S.sub.mix] the entropy of mixing and T the temperature of the GC separation (K). The more negative [DELTA][G.sub.mix] is, the better the mixing of the compounds will be (in question with the stationary phase). Since the entropy of the system always increases when the components are mixed, and the entropic term of the equation (1) is thus always negative (-T [DELTA][S.sub.mix] < 0), the mixing/solubility depends mainly on the value [DELTA][H.sub.mix]. The thermodynamic condition of the solubility of a low-molecular element in the stationary phase, or the mixing of the two substances is then:
[DELTA][H.sub.mix] < T [DELTA][S.sub.mix]. (2)
The blending will thus be the best in the case [DELTA][H.sub.mix] = 0, when also the solubility of one component in the other will be maximal as well. However, this is an ideal case. Parameters of solubility [delta] were introduced for practical purposes, numerically characterizing solubility of low-molecular and high-molecular substances (Hildebrand and Scott, 1959). A low-molecular substance a solubility parameter of which will be identical to the solubility parameter of the high-molecular substance will achieve maximal dissolution during the mixing, because [DELTA][H.sub.mix] = 0 in this case. Since cyclization increases the [delta] in the case of hydrocarbons, e.g. in the case of hexane-cyclohexane from 15.1 (hexan) to 16.8 (cyklohexan) (Brandrup and Immergut, 1975), the mixing is improved, because the parameter for high-molecular stationary phases (Mleziva, 1993) is approximately 16-18. Cyclization thus facilitates the mixing of alkylphenols or alkylbenzenes with high-molecular stationary phases, because the thermodynamic condition for mixing is better fulfilled.
On the whole, the data obtained can serve both an analytical methodology for the analysis of aromatics and phenolics, which is still topical (Naczk and Shahidi, 2004), and a deeper insight into the problem of van der Waals forces/non-covalent interactions which is also actual (Hobza et al., 2006).
Side alkyl chains of n-alkylphenols become cyclized in both polar and nonpolar stationary phases of capillary columns, with a possible formation of hydrogen bridges between the oxygen of the phenolic -OH group and a hydrogen of the methyl group of the side alkyl chain. In the case of n-alkylbenzenes, cyclization is made possible due to the interaction between the benzene ring and a hydrogen of the terminal methyl group of the alkyl. In the case of the formed aromatic-quasi-alicyclic molecules, the effect of van der Waals forces thus increases not only intramolecularly but also intermolecularly, with a consequent increase in boiling points, mainly in the case of n-alkylphenols and n-alkylbenzenes with the number of carbons in a molecule higher than 9. This results in a divergence in the retention characteristics of the mentioned compounds observed in the dependence of the logarithm of the relative retention time on the total number of carbons in the molecule. Cyclization of side alkyl chains in a dense stationary phase is a quite new phenomenon.
Grant Agency of the Academy of Sciences of the Czech Republic supported this work as the project No. IAA300460702 and Institute Research Plan Ident. Code AVOZ30460519; further, support from Ministry of Education, Youth and Sports (MSM 604 613 7304) is acknowledged.
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Pavel STRAKA (1) * Petr BURYAN (2) and Jana NAHUNKOVA (1)
(1) Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i. V Holesovickach 41, 182 09 Prague 8, Czech Republic
(2) Institute of Chemical Technology, Technicka 5, Prague 6, 166 28 Prague 6, Czech Republic
* Corresponding author's e-mail: firstname.lastname@example.org
(Received August 2007, accepted October 2007)
Table 1 Reduction of the maximum molecular size (Dmax) during the cyclization of the side chain (comparison of Dmax values for common and cyclized forms of n-alkylphenols). Molecule [D.sub.max] (nm) Position of substituent ortho meta para Common: Methylphenol 0.56 0.59 0.67 Ethylphenol 0.72 0.72 0.80 n-Propylphenol 0.82 0.83 0.91 n-Butylphenol 0.93 0.95 1.04 n-Pentylphenol 1.06 1.08 1.15 n-Hexylphenol 1.19 1.21 1.28 Cyclized on -C[H.sub.3]: Methylphenol 0.58 0.49 0.47 Ethylphenol 0.65 0.55 0.48 Propylphenol 0.72 0.61 0.57 Butylphenol 0.72 0.66 0.54 Pentylphenol 0.80 0.70 0.61 Hexylphenol 0.78 0.71 0.73 Table 2 Potential energies of covalent bonds and non-covalent interactions in ortho n-alkylphenols (common, cyclized on C[H.sub.3]-, cyclized as -C[H.sub.2]-[alpha] and -C[H.sub.2]-[beta]). Calculated by the MM+ program. Energetic terms: [E.sub.bond]-bond stretching, [E.sub.angle]-bond angle bending, [E.sub.stretch-bend]-stretch-bend (bond stretch and angle bending cross term), [E.sub.dihedral]-torsional energy, [E.sub.vdWaals]-van der Waals interactions, [E.sub.els]-the classical non-bonded electrostatic interactions (particularly dipole-dipole interactions). For [D.sub.max] see Table 1. n-Alkylphenols [E.sub.bond] [E.sub.angle] [E.sub.stretch-bend] (kJ/mol) Phenol 4.57 9.43 -0.443 Common: Methylphenol 6.90 9.68 -0.589 Ethylphenol 8.80 9.68 -0.577 n-Propylphenol 10.70 9.68 -0.577 n-Butylphenol 12.60 9.68 -0.573 n-Pentylphenol 14.50 9.68 -0.568 n-Hexylphenol 16.40 9.69 -0.568 Cyclized on C[H.sub.3]: Methylphenol 37.06 232.19 -1.986 Ethylphenol 12.93 24.32 0.180 Propylphenol 11.09 4.56 -0.042 Butylphenol 12.81 4.82 -0.004 Pentylphenol 14.53 4.22 -0.004 Hexylphenol 16.67 4.18 -0.230 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 12.93 24.32 0.180 Propylphenol 14.83 24.14 0.155 Butylphenol 16.73 24.15 0.159 Pentylphenol 18.63 24.15 0.159 Hexylphenol 20.53 24.15 0.163 Cyclized as -C[H.sub.2]-[beta]: Propylphenol 14.83 24.14 0.155 Butylphenol 12.83 4.37 -0.050 Pentylphenol 14.71 4.36 -0.046 Hexylphenol 16.64 4.37 -0.046 n-Alkylphenols [E.sub.dihedral] [E.sub.vdWaals] [E.sub.elst] Phenol -23.32 12.11 0 Common: Methylphenol -31.35 17.12 0.205 Ethylphenol -31.94 41.25 0.920 n-Propylphenol -31.94 44.24 0.920 n-Butylphenol -31.94 47.23 0.920 n-Pentylphenol -31.94 50.40 0.920 n-Hexylphenol -31.94 53.58 0.920 Cyclized on C[H.sub.3]: Methylphenol -16.79 11.39 0.004 Ethylphenol -16.75 12.09 0.786 Propylphenol -23.86 27.61 0.334 Butylphenol 2.26 49.25 0.146 Pentylphenol 8.44 210.20 0.247 Hexylphenol 4.29 - 0.096 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol -16.75 12.09 0.786 Propylphenol -17.14 14.22 0.786 Butylphenol -15.67 33.18 0.786 Pentylphenol -15.68 38.08 0.786 Hexylphenol -15.68 40.93 0.786 Cyclized as -C[H.sub.2]-[beta]: Propylphenol -17.14 14.22 0.786 Butylphenol -23.86 29.67 0.334 Pentylphenol -21.73 41.34 0.334 Hexylphenol -21.76 44.21 0.334 n-Alkylphenols [D.sub.max] (nm) Phenol 0.56 Common: Methylphenol 0.56 Ethylphenol 0.72 n-Propylphenol 0.82 n-Butylphenol 0.93 n-Pentylphenol 1.62 n-Hexylphenol 1.93 Cyclized on C[H.sub.3]: Methylphenol 0.58 Ethylphenol 0.65 Propylphenol 0.72 Butylphenol 0.72 Pentylphenol 0.79 Hexylphenol 0.78 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 0.65 Propylphenol 0.72 Butylphenol 0.82 Pentylphenol 0.88 Hexylphenol 0.94 Cyclized as -C[H.sub.2]-[beta]: Propylphenol 0.72 Butylphenol 0.81 Pentylphenol 0.89 Hexylphenol 0.99 Table 3 Potential energies of covalent bonds and non-covalent interactions in meta n-alkylphenols (common, cyclized on [CH.sub.3]-, cyclized as -[CH.sub.2]-[alpha] and -[CH.sub.2]-[beta]). Calculated by the MM+ program. For symbols see Table 2. n-Alkylphenols [E.sub.bond] [E.sub.angle] [E.sub.stretch-bend] (kJ/mol) Phenol 4.57 9.43 -0.443 Common: Methylphenol 6.90 9.68 -0.589 Ethylphenol 8.80 9.68 -0.577 n-Propylphenol 10.70 9.68 -0.577 n-Butylphenol 12.60 9.68 -0.573 n-Pentylphenol 14.50 9.68 -0.568 n-Hexylphenol 16.40 9.69 -0.568 Cyclized on C[H.sub.3]: Methylphenol 10.26 38.69 -0.961 Ethylphenol 13.81 36.63 -3.064 Propylphenol 29.75 64.02 3.703 Butylphenol 31.13 59.18 1.726 Pentylphenol 19.09 29.00 0.581 Hexylphenol 16.64 4.66 -0.038 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 13.81 36.63 -3.064 Propylphenol 15.72 36.38 -0.380 Butylphenol 17.62 36.38 -0.376 Pentylphenol 19.52 36.38 -0.376 Hexylphenol 21.42 36.38 -0.372 Cyclized as -C[H.sub.2]-/[beta]: Propylphenol 29.75 64.02 3.703 Butylphenol 31.66 63.70 3.478 Pentylphenol 33.56 63.71 3.478 Hexylphenol 35.45 63.71 3.482 n-Alkylphenols [E.sub.dihedral] [E.sub.vdWaals] [E.sub.elst] Phenol -23.32 12.11 0 Common: Methylphenol -26.33 14.57 0.113 Ethylphenol -26.92 39.44 0.113 n-Propylphenol -26.92 42.49 0.113 n-Butylphenol -26.92 45.48 0.113 n-Pentylphenol -26.92 48.66 0.113 n-Hexylphenol -26.92 51.84 0.113 Cyclized on C[H.sub.3]: Methylphenol 389.88 32.45 0.002 Ethylphenol 369.97 95.81 0.493 Propylphenol 243.10 385.13 0.159 Butylphenol -1.34 3173.33 0.054 Pentylphenol -13.30 2941.51 0.042 Hexylphenol -10.80 8006.79 0.054 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 369.97 95.81 0.493 Propylphenol 371.00 140.79 0.493 Butylphenol 373.11 1252.08 0.493 Pentylphenol 373.11 1250.91 0.493 Hexylphenol 373.11 1252.79 0.493 Cyclized as -C[H.sub.2]-/[beta]: Propylphenol 243.10 385.13 0.159 Butylphenol 243.36 388.27 0.159 Pentylphenol 245.48 397.56 0.159 Hexylphenol 245.48 400.36 0.159 n-Alkylphenols [D.sub.max] (nm) Phenol 0.56 Common: Methylphenol 0.59 Ethylphenol 0.72 n-Propylphenol 0.83 n-Butylphenol 0.95 n-Pentylphenol 1.08 n-Hexylphenol 1.21 Cyclized on C[H.sub.3]: Methylphenol 0.49 Ethylphenol 0.55 Propylphenol 0.61 Butylphenol 0.66 Pentylphenol 0.69 Hexylphenol 0.71 Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 0.55 Propylphenol 0.66 Butylphenol 0.66 Pentylphenol 0.77 Hexylphenol 0.81 Cyclized as -C[H.sub.2]-/[beta]: Propylphenol 0.61 Butylphenol 0.71 Pentylphenol 0.75 Hexylphenol 0.85 Table 4 Potential energies of covalent bonds and non-covalent interactions in n-alkylbenzenes cyclized into the position meta with respect to the substituent (common, cyclized on C[H.sub.3]-, cyclized as -C[H.sub.2]-[alpha] and -C[H.sub.2]-[beta]). Calculated by the MM+ program. For symbols see Table 2. n-Alkylbenzenes [E.sub.bond] [E.sub.angle] [E.sub.stretch-bend] (kJ/mol) Benzene 4.573 9.434 -0.443 Common: Methybenzene 7.060 0.247 -0.142 Ethylbenzene 8.958 0.247 -0.130 n-Propylbenzene 10.860 0.247 -0.130 n-Butylbenzene 12.757 0.247 -0.125 n-Pentylbenzene 14.659 0.247 -0.125 n-Hexylbenzene 16.561 0.247 -0.125 Cyclized on C[H.sub.3]: Methylbenzene 7.829 123.134 -3.582 Ethylbenzene 10.266 29.465 -2.274 Propylbenzene 12.858 21.611 -1.058 Butylbenzene 27.337 50.051 2.479 Pentylbenzene 30.443 49.667 0.982 Hexylbenzene 17.217 5.304 -0.117 Cyclized as -C[H.sub.2]-[alpha]: Ethylbenzene 10.266 29.465 -2.274 Propylbenzene 12.344 29.565 -2.182 Butylbenzene 14.241 29.565 -2.182 Pentylbenzene 16.143 29.565 -2.178 Hexylbenzene 18.045 29.565 -2.174 Cyclized as -C[H.sub.2]-[beta]: Propylbenzene 12.858 21.611 -1.058 Butylbenzene 14.755 21.657 -1.058 Pentylbenzene 16.657 21.657 -1.053 Hexylbenzene 18.555 21.657 -1.049 n-Alkylbenzenes [E.sub.dihedral] [E.sub.vdWaals] [E.sub.elst] Benzene -23.324 12.114 0 Common: Methybenzene -26.334 14.852 0 Ethylbenzene -26.919 39.727 0 n-Propylbenzene -26.919 42.778 0 n-Butylbenzene -26.919 45.771 0 n-Pentylbenzene -26.919 48.956 0 n-Hexylbenzene -26.919 52.137 0 Cyclized on C[H.sub.3]: Methylbenzene 194.742 41.503 0 Ethylbenzene 292.847 34.230 0.560 Propylbenzene 305.633 54.081 0.242 Butylbenzene 185.379 257.722 0.159 Pentylbenzene -2.504 3102.939 0.134 Hexylbenzene -0.573 - 0.125 Cyclized as -C[H.sub.2]-[alpha]: Ethylbenzene 292.847 34.230 0.560 Propylbenzene 294.372 51.493 0.560 Butylbenzene 297.114 456.540 0.560 Pentylbenzene 297.114 457.585 0.560 Hexylbenzene 297.114 458.588 0.560 Cyclized as -C[H.sub.2]-[beta]: Propylbenzene 305.633 54.081 0.242 Butylbenzene 308.701 55.765 0.242 Pentylbenzene 311.523 78.927 0.242 Hexylbenzene 311.523 81.619 0.242 n-Alkylbenzenes [D.sub.max] (nm) Benzene - Common: Methybenzene 0.59 Ethylbenzene 0.72 n-Propylbenzene 0.82 n-Butylbenzene 0.95 n-Pentylbenzene 1.06 n-Hexylbenzene 1.19 Cyclized on C[H.sub.3]: Methylbenzene 0.47 Ethylbenzene 0.51 Propylbenzene 0.57 Butylbenzene 0.62 Pentylbenzene 0.66 Hexylbenzene 0.69 Cyclized as -C[H.sub.2]-[alpha]: Ethylbenzene 0.51 Propylbenzene 0.62 Butylbenzene 0.72 Pentylbenzene 0.81 Hexylbenzene 0.95 Cyclized as -C[H.sub.2]-[beta]: Propylbenzene 0.57 Butylbenzene 0.65 Pentylbenzene 0.75 Hexylbenzene 0.84 Table 5 Energies of van der Waals interactions ([E.sub.vdWaals], kJ/mol)in the molecules of n-alkylphenols and n-alkylbenzenes. Calculated by the MM+ program. Positions "ortho", "meta", "para" at n-alkylbenzenes mean cyclization into the positions with respect to the substituent. n-Alkylphenols ortho meta para Common: Methylphenol 17.117 14.57 14.6 Ethylphenol 41.248 39.44 39.47 n-Propylphenol 44.237 42.49 42.51 n-Butylphenol 47.226 45.48 45.51 n-Pentylphenol 50.402 48.66 48.69 n-Hexylphenol 53.583 51.84 51.87 Cyclized on C[H.sub.3]: Methylphenol 11.395 32.45 44.96 Ethylphenol 12.089 95.81 109.4 Propylphenol 27.609 385.1 411.3 Butylphenol 49.249 3173.0 1037 Pentylphenol 210.2 2942 Hexylphenol - 8007 1132 - Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 12.089 95.81 109.4 Propylphenol 14.22 140.8 735.8 Butylphenol 33.177 1252 129.3 Pentylphenol 38.076 1251 132.1 Hexylphenol 40.931 1251 135 Cyclized as -C[H.sub.2]-[beta]: Propylphenol 14.22 385.1 411.3 Butylphenol 29.665 388.3 479.1 Pentylphenol 41.34 397.6 3399 Hexylphenol 44.208 400.4 3395 n-Alkylbenzenes "ortho" "meta" "para" Common: Methylbenzene 14.852 14.85 14.85 Ethylbenzene 39.727 39.73 39.73 n-Propylbenzene 42.778 42.78 42.78 n-Butylbenzene 45.771 45.77 45.77 n-Pentylbenzene 48.956 48.96 48.96 n-Hexylbenzene 52.137 52.14 52.14 Cyclized on C[H.sub.3]: Methylbenzene 10.396 41.5 23.99 Ethylbenzene 11.227 34.23 46.87 Propylbenzene 14.254 54.08 67.42 Butylbenzene 27.642 257.7 339.3 Pentylbenzene 64.514 3103 832.2 Hexylbenzene 476.77 - 905.6 Cyclized as -C[H.sub.2]-[alpha]: Ethylbenzene 11.227 34.23 46.87 Propylbenzene 11.608 51.49 54.72 Butylbenzene 21.916 456.5 216 Pentylbenzene 24.658 457.6 218.1 Hexylbenzene 27.362 458.6 220 Cyclized as -C[H.sub.2]-[beta]: Propylbenzene 11.608 54.08 67.42 Butylbenzene 16.386 55.77 70.17 Pentylbenzene 27.312 78.93 132.4 Hexylbenzene 29.783 81.62 134.9 Table 6 Energies of van der Waals interactions ([E.sub.vdWaals], kJ/mol) in the molecules of n-alkylphenols and n-alkylbenzenes. Calculated by the AMBER program. Positions "ortho", "meta", "para" at n-alkylbenzenes mean cyclization into the positions with respect to the substituent. n-Alkylphenols ortho meta para Common: Methylphenol 17.54 13.53 13.58 Ethylphenol 36.17 35.04 35.09 n-Propylphenol 36.54 35.48 35.53 n-Butylphenol 37.13 36.07 36.13 n-Pentylphenol 37.90 36.86 36.91 n-Hexylphenol 38.71 37.67 37.72 Cyclized on C[H.sub.3]: Methylphenol 14.93 43.83 65.28 Ethylphenol 11.05 141.61 175.12 Propylphenol 19.08 2975.8 6246.6 Butylphenol 38.38 4 x [10.sup.6] 9 x [10.sup.4] Pentylphenol 703.1 4 x [10.sup.6] - Hexylphenol - 4 x [10.sup.10] - Cyclized as -C[H.sub.2]-[alpha]: Ethylphenol 11.05 141.61 175.12 Propylphenol 11.42 249.91 17755 Butylphenol 37.26 31143 195.47 Pentylphenol 41.70 31142 195.82 Hexylphenol 42.22 31142 196.36 Cyclized as -C[H.sub.2]-[beta]: Propylphenol 19.08 2976 6247 Butylphenol 19.35 2977 6387 Pentylphenol 28.03 2982 8 x [10.sup.6] Hexylphenol 28.44 2983 8 x [10.sup.6] n-Alkylbenzenes "ortho" "meta" "para" Common: Methylbenzene 13.90 13.90 13.90 Ethylbenzene 35.43 35.43 35.43 n-Propylbenzene 35.87 35.87 35.87 n-Butylbenzene 36.48 36.48 36.48 n-Pentylbenzene 37.26 37.26 37.26 n-Hexylbenzene 38.07 38.07 38.07 Cyclized on C[H.sub.3]: Methylbenzene 12.92 55.41 24.34 Ethylbenzene 14.35 40.43 53.46 Propylbenzene 11.52 61.62 74.65 Butylbenzene 16.90 1082.8 4182.5 Pentylbenzene 61.29 6 x 35913 [10.sup.6] Hexylbenzene - - - Cyclized as -C[H.sub.2]-[alpha]: Ethylbenzene 14.35 40.43 53.46 Propylbenzene 13.74 65.87 60.95 Butylbenzene 21.82 5888.8 777.48 Pentylbenzene 22.05 5887.9 777.15 Hexylbenzene 22.44 5887.1 777.06 Cyclized as -C[H.sub.2]-[beta]: Propylbenzene 11.52 61.62 74.65 Butylbenzene 11.85 61.63 75.59 Pentylbenzene 20.19 94.76 194.70 Hexylbenzene 20.24 95.01 194.76 Table 7 Boiling points of normal and cyclic hydrocarbons [C.sub.3]-[C.sub.8] and energies of intramolecular van der Waals interactions. Alkane [T.sub.b] [E.sub.vdWaals] [E.sub.vdWaals] ([degrees]C) (MM+)(kJ/mol) (AMBER)(kJ/mol) n-Propane -44.5 8.469 1.835 n-Butane -0.5 11.867 2.796 n-Pentane 36.15 15.132 3.666 n-Hexane 68 18.363 4.514 n-Heptane 98.34 21.577 5.355 n-Octane 125.5 24.787 6.191 Cyclopropane -33.5 0.134 0.067 Cyclobutane 13 11.265 1.233 Cyclopentane 49.262 14.768 2.399 Cyclohexane 81 22.121 5.338 Cycloheptane 118.48 204.757 721.522 Cyclooctane 150 501.123 7839.966 Table 8 Energies of van der Waals interactions in the association of two molecules of a common n-alkylphenols and n-alkylbenzenes in comparison with those of two non-associated (isolated) molecules. Calculated by the AMBER method. Compound [E.sub.vdWaals (associate)] (kJ/mol) Phenol 2.189 x [10.sup.10] ortho n-Methylphenol-ortho 2.427 x [10.sup.10]-8.945 n-Hexylphenol x [10.sup.13] para n-Methylphenol-para 2.943 x [10.sup.9]-4.193 n-Hexylphenol x [10.sup.12] Benzene 2.291 x [10.sup.15] Compound [E.sub.vdWaals(2 isolated molecules)] (kJ/mol) Phenol 24.512 ortho n-Methylphenol-ortho 35.087-77.414 n-Hexylphenol para n-Methylphenol-para 27.162-75.441 n-Hexylphenol Benzene 25.076
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|Author:||Straka, Pavel; Buryan, Petr; Nahunkova, Jana|
|Publication:||Acta Geodynamica et Geromaterialia|
|Date:||Jan 1, 2008|
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