AM1 study of conformational properties of Z, Z-, E, E- and E, Z-cyclodeca-1,6-diene

Abstract

An investigation employing the AM1 semiempirical SCF MO method to calculate structure optimization and conformational interconversion pathways for the three geometrical isomers of cyclodeca-1,6-diene has been undertaken. The Z, Z-isomer is calculated to be 10.3 kJ mol −1 more stable than the E, E-isomer, while the E, Z-isomer is 13.3 kJ mol −1 less stable than the Z, Z-isomer. A chair conformation with C 2 h symmetry is found to be the most stable geometry for Z, Z-cyclodeca-1,6-diene ( 1). The boat form, with C 2 v symmetry, is only 3.5 kJ mol −1 less stable than the chair conformer. Conformational interconversion of these forms requires 52 kJ mol −1. The crown form of the parallel family of E, E-cyclodeca-1,6-diene ( 2) is 7.4 kJ mol −1 more stable than the plane-symmetrical chair–chair–boat geometry. Two axial-symmetrical conformations are found for the crossed family of 2. The twist-boat conformation, with a nonintersecting C 2 axis, is calculated to be 10.3 kJ mol −1 less stable than the crown conformation. The unsymmetrical boat–chair ( 3-BC) conformation of E, Z-cyclodeca-1,6-diene ( 3) is calculated to be 16.6 kJ mol −1 more stable than the axial-symmetrical twist form. The interconversion of 3-TC and twist conformations take place via an unsymmetrical transition state, which is 45.6 kJ mol −1 less stable than 3-TC. The barrier for swiveling of the trans double bond through the unsaturated bridge in compounds 2 and 3 is calculated to be 102.5 and 61.9 kJ mol −1, respectively.