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New symbols for reaction mechanisms.

New symbols for reaction mechanisms During a chemical reaction, bonds between atoms are made and broken. For over 30 years, chemists have been using symbols devised by Sir Christopher K. Ingold for categorizing reactions according to patterns of bond transformations. These symbols consist of a limited cast of letters and numbers that represent chemical events such as an atom substituting for another other on a molecule, the elimination of a group of atoms from a molecule and how many molecules "touch" during a particular reaction. But Ingold's system "has become unwieldly and, in some cases, ambiguous," says Robert D. Guthrie of the University of Kentucky in Lexington.

At regional offices of the International Union of Pure and Applied Chemistry (IUPAC), chemists soon will be able to review a proposal for a new system of symbols for chemical reactions that a high IUPAC official says is "more rational and comprehensive" than Ingold's system. The new system, which was proposed by Guthrie in 1975 and has since been refined by an IUPAC committee of which he is a member, will probably be approved by the IUPAC at the end of next summer. Guthrie argues the new symbolic system is a "more logical approach" to describing reaction mechanisms that is "closer to how organic chemists think." He says that the symbols -- a refined set of numbers, letters and punctuations--describe more clearly the sequence of bond making and breaking during chemical reactions. Furthermore, Guthrie says that simply using the new symbols could stimulate researchers to ask important experimental questions that they would otherwise overlook.

Joseph Bunnett, president of the organic chemistry division of IUPAC, says the new system is "sailing smoothly" through the organization's involved approval process. Just how far the system gets once it is approved will depend more on how effectively Guthrie and the IUPAC commission can market it, Bunnett adds.
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Title Annotation:chemical reaction
Publication:Science News
Date:Nov 15, 1986
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