THE MICHAEL REACTION IN NON-ALKALINE MEDIA. V. EFFECT OF STRUCTURE ON THE RATE AND MECHANISM OF ADDITION OF 1,1-DINITROCARBANIONS TO METHYL ACRYLATE,
Abstract
The kinetics of the addition of a series of substituted 1,1-dinitromethide ions to methyl acrylate were studied in 50% dioxane and in water. The requirement for acid catalysis in these Michael additions was defined as a lowering of the free energy of the transition state for the reversal of the initially formed carbanion RC(NO2)2CH2CHCO2CH3. This can be accomplished by a substituent R which is able to delocalize negative charge by a resonance interaction. For borderline cases, the rate of protonation of the carbanion RC(NO2)2CH2CHCO2CH3 may be a deciding factor in effecting a change from an acid catalyzed to an uncatalyzed reaction. A comparison of the specific rate and activation parameters for fluorodinitromethide ion with alkyl, chloro and hydrogen dinitromethide ions shows that the 2000-fold increase in rate for R = F is due to a 5 kcal./mo1 decrease in Delta H*. This enhanced nucleophilicity is attributed to a destabilization of an sp2-hybridized carbon by an alpha-fluorine substituent. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 15, 1970
- Accession Number
- AD0710991
Entities
People
- Hugh B. Pickard
- Lloyd A. Kaplan
Organizations
- Naval Ordnance Laboratory