Question
Which one of the following will react fastest with $${H_2}$$ under catalytic hydrogenation condition ?
A.
B.
C.
D.
Answer :
Solution :
TIPS/Formulae :
The relative rates of hydrogenation decreases with increase of steric hinderance.
$${R_2}C = C{H_2} > RCH = CHR > {R_2}C = CHR > {R_2}C = C{R_2}$$
Among the four olefins, (a) and (b) are less stable ( Saytzeff rule ). Further in (a), the bulky alkyl groups are on same side ( $$cis$$ - isomer ), hence it is less stable.
TIPS/Formulae :
The relative rates of hydrogenation decreases with increase of steric hinderance.
$${R_2}C = C{H_2} > RCH = CHR > {R_2}C = CHR > {R_2}C = C{R_2}$$
Among the four olefins, (a) and (b) are less stable ( Saytzeff rule ). Further in (a), the bulky alkyl groups are on same side ( $$cis$$ - isomer ), hence it is less stable.