A new global minimum for [12]annulene has been computationally located. This mono-
trans minimum
5 (CCCCCT) is computed to be 1.5 kcal/mol more stable (CCSD(T)/cc-pVDZ//BHHLYP/6-311+G**)than the known tri-
trans isomer
1 (CTCTCT) and 2.4 kcal/mol lower than the di-
trans isomer
4 (CCTCCT),for which there is indirect evidence. The barriers for several rearrangements of
5 were all computed tobe above 15 kcal/mol, indicating that direct experimental characterization of
5 should be possible. Thecomputed barriers for the dynamic processes (including conformational automerization) coupled withcomputed
1H NMR shift values should aid in the future characterization of this [12]annulene isomer.