Question

1-aldo-2-methylcyclohex-1-ene is passed through n2h4 in H2O 2 solution. The product is 1-aldo-2-methylcyclohexane with the syn addition of hydrogen atoms. Why the hydrogen atoms are added from the same side?

Answer 1

Here's what I find.

Explanation:

The hydrogen peroxide oxidizes the hydrazine to diimide (diazene).

`"N"_2"H"_4 + "H"_2"O"_2 → "HN=NH" + "2H"_2"O"`

The trans form of diimide is more stable than the cis, but it is the cis form that takes part in the reaction.

The mechanism involves a cyclic, concerted [4+2] intramolecular addition.

The geometry of the transition state requires the diimide to deliver both hydrogen atoms simultaneously to the same side of the cyclohexene ring (syn addition).

Thus, 2-methylcyclohexenecarbaldehyde forms
cis-2-methylcyclohexanecarbaldehyde.