A theoretical approach to substituent effects. Stabilities and rotational barriers of β-substituted ethyl anions

Addy Pross, Leo Radom

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Abstract

Ab initio molecular orbital theory is used to study substituent effects in a series of substituted ethyl anions, XCH2CH2- (X = Li, BeH, BH2, CH3, NH2, OH and F). All substituents stabilize the anion relative to the corresponding neutral ethane. For electronegative substituents (NH2, OH and F) as well as CH3, this stabilization is achieved through enhanced hyperconjugative donation from the occupied 2p(C-) orbital to a vacant π*(CH2X) or π*(CH2) orbital; electropositive groups (Li, BeH and BH2) stabilize the anion primarily by 1, 3-overlap between the occupied 2p(C-) orbital and the vacant 2p(X) orbital where such an interaction is possible. The importance of 1, 3-interactions contrasts with the situation for cations XCH2CH2+in which hyperconjugative interactions appear to be dominant.

Original languageEnglish
Pages (from-to)241-248
Number of pages8
JournalAustralian Journal of Chemistry
Volume33
Issue number2
DOIs
StatePublished - 1 Jan 1980

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