H. Tavakol, S. Amiraslanzadeh, Study of Isomery Scheme in Acetyl Hydrazides by DFT Calculations, 14^th Iranian Physical Chemistry Conference, Kish Iceland, Kish, February 2011

Abstract

The relative stabilities of isomers in the gas phase are found to be as 1, 2E, 2Z, 4Z, 4E, 6EE, 5, 6EZ, 6ZZ, 6ZE, 3E, 7E, 9E, 3Z, 7Z, 9Z, 8E, and 8Z. In addition, in all tautomers except tautomer 4, the E isomer is more stable than Z isomer. Viewing results, it can be observed that in isomer 4E, there is an unfavorable spatial interaction between methyl and formyl groups. This interaction can be responsible for the less stability of 4E versus 4Z. ∆G between cis and trans isomers is variable from 2.03 in tautomers 2 to 11.4 in tautomers 8. Observing optimized structure of 8Z shows that there is unfavorable interaction between methylene and hydroxyl groups. This interaction (between large groups) is responsible for large instability of 8Z versus 8E while in tautomers 2, only two hydrogens (small atoms) have spatial interaction in Z isomer. Therefore, it is not strange that ∆G between 2E and 2Z will be very small.

To examine solvent effect, the relative stabilities have been calculated in different solvents (acetone, chloroform, cyclohexane and DMSO). The relative stabilities in solvents are similar to those in the gas phase except in 6EZ and 9E because these isomers have respectively the minimum and maximum average ∆G solvations among all isomers.