Abstract: The study aims to discuss the photochemical isomerization of 2-cyanothiophene. The reaction was described several years ago, and the possible formation of Dewar 2-cyanothiophene was proposed. It has been suggested that the photochemical isomerization of pentatomic aromatic heterocycles occurring through the first excited singlet state proceeds via the formation of a Dewar isomer. CASSCF calculations have been performed to investigate this process. The CASSCF study of the photoisomerization of 2-cyanothiophene showed the presence of a conical intersection in the excited state, allowing the formation of Dewar 2-cyanothiophene. A transition state of 0.68 eV permits the formation of the isomeric Dewar 3-cyanothiophene, which can be converted into 3-cyanothiophene through a transition state of 1.40 eV. These results support the suggestion that all photochemical isomerizations of pentatomic aromatic heterocycles occurring through the first excited singlet state involve Dewar intermediates.
Auria et al. (Fri,) studied this question.
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