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

An investigation employing the AM I semiempirical SCF MO method to calculat e structure optimization and conformational interconversion pathways for th e three geometrical isomers of cyclodeca-1,6-diene has been undertaken. The ZZ-isomer is calculated to be 10.3 U mol(-1) more stable than the EE-isome r, while the E,Z-isomer is 13.3 U mol(-1) less stable than the Z,Z-isomer. A chair conformation with C-2h symmetry is found to be the most stable geom etry for Z,Z-cyclodeca-1,6-diene (1). The boat form, with C-2v symmetry, is only 3.5 W mol(-1) less stable than the chair conformer. Conformational in terconversion of these forms requires 520 mol(-1). The crown form of the pa rallel 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 confor mation, with a nonintersecting C-2 axis, is calculated to be 10.3 U mol(-1) less stable than the crown conformation. The unsymmetrical boat-chair (3-B C) 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 interconvers ion of 3-TC and twist conformations take place via an unsymmetrical transit ion 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 compou nds 2 and 3 is calculated to be 102.5 and 61.9 U mol(-1), respectively. (C) 2001 Elsevier Science BN. All rights reserved.