Question

Why 2,3 Dimethyl but-2-ene more stable than But-2-ene ?
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Answer 1

2-butene is more stable the 1-butene because the terminal methyl group has three C-H bonds and the bonding orbitals associated with those C-H bond is donating into the pi system and this is the so-called hyperconjugation effect. One effect of it is the C-H bond nearby to the pi system is weaker then the regular sp3 hybridized C-H bond and the methyl group is a part of allylic system which is well known for its weak C-H bond even the pka of C-H bond of allylic system is less then the regular C-H bond