Question

Arrange alkanes alkenes and alkynes in increasing order of the c-h bond lengths Give reason for the same Thnx

Answer 1

C-H bond length is shortests in alkyne and longest in alkane and order will be:
alkane > alkene > alkyne
The reason is that in case of alkyne H is bonded to sp hybridised carbon where s character is 50%.
In caseof alkene it is bonding of H with sp2 hybridised carbon. means 33% s character.
in case of alkane it is bonding of H with sp3 hybridised carbon means 25% s character.
And we know that s orbital is closest to nucleus. More s character means more close to nucleus and shorter will be bond in turn shorter will be bond length.