Nucleophilic carbonyl addition reaction trajectory

The trajectory of nucleophilic attack upon the double bond of VIII is quite close to that of the addition of nucleophiles to the carbonyl bond. For the addition reaction of the hydride-ion (Y = H) to ethylene (R = Z = H), and propene (R = CH3) the angle d is 123° (according to the ab initio 3-21G calculations in Ref. [23]. The driving force of the reaction is the charge transfer from the electron lone pair orbital of the nucleophile Y to the 7i -orbital of olefine. The latter has, unlike the orbital n Q (see Fig. 4.1), no loop on the a-atom of carbon and is delocalized, which diminishes the overlap integral and thereby the energy of interaction AE from Eq. (4.10) of the nucleophile with alkene as compared to the energy of interaction with the carbonyl... 

Chiral a-methyl aldehydes (43) show exceptional diastereofacial preferences in their Lewis acid mediated reactions with enol silanes (equation i6) 2i 25c-26-64 selected data are reported in Table 8. The reason for this selectivity may be due to an approach trajectory of the nucleophile closer to the stereocenter when the carbonyl group is bound to the Lewis acid. Additions to chiral a-alkoxy aldehyde (48) were studied with both nonstereogenic (equation 17 Table 9) and stereogenic enol silanes (equation 18 Table 10). (Stereogenic and nonstereogenic are defined according to Mislow and Siegel.) ... 

B3LYP/6-31+G level calculations on the reaction between a-bromoacetophenones and hydroxide ion in the gas phase suggest that two products (from substitution of the or-bromine and addition to the carbonyl carbon) form from a single transition state where the OH nucleophile is associated with both the C and the carbonyl carbon. Trajectory calculations have shown that substrates with a more electron-withdrawing substituent than meta-C on the benzene ring react at the carbonyl group, while those with more electron-donating substituents react at bromine. 

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