Monday, January 28, 2008

IIT JEE Revision - Acidity of alkenes

Alkynes are weakly acidic.

Compared to alkynes, alkenes are still weak in acidic behaviour. Practically they do not shown any acidic behaviour.

The acidic property is because of s character.

Alkynes are sp hybridized. (50% s character)
Alkenes are sp² hybridized (33% s character)
Because of lesser s character, these carbon atoms are much less electronegative than the carbon atoms taking part in the triple bond.

Therefore, the release of H+ ion from an alkene molecule is difficult and they do not show acidic character.

In term of Ka

Alkynes have 10^-26 and

alkenes have 10^-36.

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