Antiaromaticity in Relation to 1,3,5,7-Cyclooctatetraene Structures

摘要

An isodesmic energy analysis has been carried out at the MP2/6-31G*//HF/3-21Glevel for the non-planar ground state (1) of 1,3,5,7-cyclooctatetraene and for two planar forms, one having complete pi delocalization (2) and the other having alternating single and double bonds (3). 1 is found to have a considerable degree of stabilization, which is attributed to limited pi delocalization. The polyene 3 is the more stable of the two planar forms; it is a transition state in the inversion between two possible non-planar structures. 2 is found to be a triplet at the Hartree-Fock level, and is a critical point on an alternate pathway between the two possible arrangements of alternating single and double bonds in 3. Both 2 and 3 have negative isodesmic energies, indicating the presence of stabilizing factors. 1,3,5,7-Cyclooctatetraene, Antiaromaticity.