engleski

Multireference AQCC study of Hoffman-Bošković bond-stretch isomerization reactions

Bond stretch isomerization is a phenomenon encompassing molecular systems occuring in two forms, which in turn differ in the length(s) of one or several bonds, other structural parameters being practically constant. The resulting isomers are rare, but their properties are distinctly different as a consequence of different bonding patterns. A typical example is provided by dibenzo[1, 2:3, 4]cyclobutadiene, where a pair of isomers possesses either a localized benzene ring or a quasi[10]annulene structure with pi-electrons delocalized over the molecular rim. A salient feature of all bond-stretch isomers is that they require explicit account ot the electron correlation energy at realtively high level of theory. A method of choice is the multireference average quadratic coupled cluster approach, because it is capable of optimizing structural parameters along the isomerization reaction pathways. In larger molecular systems a reasonable alternative is given by the CASPT2 method. Particular attention will be paied to cyclobutadiene and its cyano and fluoro derivatives. A difference between the bond-stretch and bond-shift isomers will be discussed in some detail.

bond-stretch isomers; MR-AQCC method

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