Conformational properties of (Z,Z)-,(E,Z)-,and(E,E)-Cycloocta-1,4-dienes

摘要

Ab initio calculations at the HF/6-31G* level of theory for geometry optimization and the MP2/6-31G*//HF/6-31G* level for a single point total energy calculation are reported for (Z,Z)-,(EZ)-,and 9E,E)-cycloocta-1,4-dienes.The C_2-Symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6kJ·mol~(-1) more stable than the C_s-symmetric boat-chair form;the calculated energy barrier for ring inversion of the twist-boat conformation via the C_s-symmetric boat-boat geometry is 19.1 kJ·mol~(-1).Interconversion between twist-boat and boat-chair conformations take splace via a half-chair(C_1) transition state which is 43.5kJ·mol~(-1)above the twist-boat form.The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calcualted to be by 18.7 kJ·mol~(-1) more stable than the unsymmetrical boat-chair form.The claculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol~(-1),whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6kJ·mol~(-1).The C_S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to by 16.5 kJ·mol~(-1) more stable than the C_S-symmetric boat-chair form.Intercoversion of crown and boat-chair takes place via a chair(C_S) transition state which is 37.2kJ·mol~(-1) above the crown conformation.The axial-symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol~(-1) less stable than the crown conformation.