A Theoretical Study of the Favorskii Rearrangement. Calculation of Gas-Phase Reaction Paths and Solvation Effects on the Molecular Mechanism for the Transposition of the α-Chlorocyclobutanone

Abstract

The molecular mechanism of the α-chlorocyclobutanone transposition to yield cyclopropanecarboxylic acid, as a model of the Favorskii rearrangement, has been theoretically characterized in vacuo by means of ab initio molecular orbital procedures at the Hartree−Fock (HF) level of theory with the 6-31G* and 6-31+G* basis sets. The electron correlation has been estimated at the MP2/6-31G* level and calculations based on density functional theory, BLYP/6-31G*. The solvent effects are included at HF/6-31G* level by means of a polarizable continuum model. The questions related to the two accepted molecular mechanisms, the semibenzilic acid and the cyclopropanone transpositions, as well as the competition between both reaction pathways are addressed in this investigation. The dependence of the geometries of the stationary structures along the corresponding reaction pathways and the transition vectors associated with the transition structures upon theoretical methods is discussed. The analysis of the results shows that the electrostatic solute−solvent interactions modify appreciably the topology of the potential energy surface. The cyclopropanone mechanism is stabilized with respect to the semibenzilic acid mechanism, but this latter remains the energetically favorable reactive channel both in vacuo and in solution. The semibenzilic acid mechanism is a two-step process and the rate-limiting step corresponds to the nucleophilic attack of the hydroxyl ion on the carbon atom of the carbonyl group belonging to the α-chlorocyclobutanone ring. In the cyclopropanone mechanism three transition structures appear along the energy profile and the rate-limiting step is the dehydration process of the bicyclo[1.1.0]2-butanone intermediate with concomitant ring contraction and formation of the cyclopropanecarboxylic acid product.

Polarization Effects in Aqueous and Nonaqueous Solutions

“…14,[31][32][33][34][35][36][37][38][39][40][41][42] The accurate prediction of these phenomena poses an interesting challenge to theory. One approach to this problem is to treat both the solute and a significant number of solvent molecules explicitly using suitably high levels of electronic structure theory.…”

Theoretical investigation of mono- and bi-function alkylating agents transformed from nitrosodimethylamine derivatives

“…The authors observed that this stepwise pathway is similar to the Favorskii rearrangement reaction [24][25][26]. As shown in Fig.…”

“…As a result of the finding of the di-region theory, the authors propose an alternate pathway of AMMN transformation that leads to a bi-functional alkylating agent which can induce cross-linkage between DNA complementary pair bases. This novel pathway involves an intramolecular rearrangement and is similar to the Favorskii rearrangement reaction [24][25][26]. …”

Ab initio and Density Functional Calculations on the Ring-Chain Tautomerism of γ-Oxocarboxylic Acids

“…However, in some cases (e.g. 9 ), solvation free enthalpies obtained with this basis set (both HF or B3LYP) appear to be unrealistic (for problems with basis sets containing diffuse functions in solvation energy calculations, see ref 35…”