Vinyl Carbanion Stability

A carbanion is an anion in which carbon is trivalent forms three bonds and bears a formal negative charge in at least one significant resonance form.

Vinyl carbanion stability.

The vinyl cation has an intense ir peak at 1987 cm 1 for the c c stretching. Allylic 3º 2º 1º methyl alkenyl vinyl aryl electron poor electrophilic acidic carbon radicals. Stability of carbocation intermediates. Class structure stability pattern carbocations.

Stability order of carbanions decreases as we move from primary to tertiary anion because due to i effect of methyl groups there is an increased intensity of negative charge on central carbon of tertiary carbanion which further makes it unstable. We know that the rate limiting step of an s n 1 reaction is the first step formation of the this carbocation intermediate. The observation of enzyme catalyzed deuterium exchange via a stabilized carbanion provides convincing evidence for the decarboxylation of orotidine 5 monophosphate omp by ompdc to give the same carbanion intermediate. Allylic 3º 2º 1º methyl alkenyl vinyl aryl electron poor electrophilic acidic carbanions.

But in any case the transition state leading to the phenyl carbanion will be more stable than the transition state leading to the vinyl carbanion because. Allylic carbocations are able to share their burden of charge with a nearby group through resonance. Certain carbanions also bond strongly to transition metals particularly those in low oxidation states through a combination of σ and π bonding with the ligand carbanion donating an unshared pair to form a σ bond or in the case of alkenes one or more pairs of π electrons to give dπ pπ bonding to the metal and receiving electron. More importantly the bond angles between the vinyl cation carbons and the first carbon of the alkyl substituted was measured to be approximately 180 o.

A simple allylic system will have just one pi bond. Factors that stabilize them will speed up reaction rates. The rate of this step and therefore the rate of the overall substitution reaction depends on the activation energy for the process in which the bond between the carbon and the leaving group breaks and a carbocation forms. Stability of vinyl cations.

The data show that yeast ompdc stabilizes the bound vinyl carbanion by at least 14 kcal mol. This is very very unstable and ranks under a methyl carbocation in stability. A vinyl carbocation has a positive charge on the same carbon as the double bond.