DFT Study on the Photoisomerization of Carvone

DFT calculations (B3LYP/6-311G+(d,p)) on the photoisomerization of carvone were in agreement with the mechanism proposed by Büchi in an article published in 1957. The reaction occurred in the first excited triplet state and allowed the formation of a triplet biradical intermediate due to the coupling of terminal olefinic carbon atom on the isopropylene chain with the carbon atom in b position to the carbonyl group. This transformation occurred through a very small transition state (0.22 eV). The coupling of the radical carbon atoms allowed the formation of the observed tricyclic terpenes. Attempts to identify the presence of a conical intersection in the first excited singlet state performing calculations at CASSCF(6,6) level of theory failed.