Theoretical calculations allylic substitution

Theoretical calculations of the reactions of CH3SSR (R = H or CH3) with fluoride, hydroxide or allyl anion in the gas phase have been performed to determine the mechanism for both elimination and substitution reactions.6 The elimination reactions have... 

The allyl radical has been extensively studied by e.s.r. and the distribution of the unpaired electron over the 7r-orbital system has been the subject of experimental measurement and many theoretical calculations (Fessenden and Schuler, 1963 Kochi and Krusic, 1968 Heller and Cole, 1962). However, there is no direct evidence available on the effect of methyl substitution at the terminal positions on the distribution of the unpaired electron. 

A unified theoretical explanation using molecular orbital theory has been proposed. Grimme [65] investigated the PFR of phenyl acetate as well as the photo-Claisen rearrangement of allyl phenyl ether and the 3-cleavage of para-substituted phenoxyacetones. A unified description of the three reactions has been invoked according to MNDOC-CI and AMl/AMl-HE calculations. No matter what ex-... 

The 5n2 reactions of y-substituted allyl chlorides where the nucleophile is a free anion and an ion pair were studied theoretically at the HF/6-31+G level of theory.10 The calculations showed that the free ion, S N2 reaction proceeds through a transition state (7) with significant positive charge on Ca and little conjugation with the n-system. Placing substituents on Cy of the free ion reactions gave computed Hammett p values of -3.3 and -4.6 for the trans- and ds-conformation reactions, respectively. The transition states (8) for the ion pair reactions, on the other hand, have considerable positive charge on both Ca and Cy and the computed Hammett p value is +18.8. 

Theoretical support was obtained to explain the experimental results observed with a-chloro- or a-bromo-substituted pinacolboronates (5)6 (Scheme 3.IX). When calculations were performed on the reaction between the a-fluoro-substituted allyl-boronic acid and formaldehyde, transition state A, in which fluorine atom occupies an axial position, was found to be more stable than transition state B by 3.5 kcal/mol. 

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