Q.How is benzamide converted into benzylamine ?

Reduction of Amides: From Intuition to Precision

Imagine you have a molecule with a carbonyl group ($\ce{C=O}$) that is directly attached to a nitrogen atom — that's an amide. The carbonyl is electron-deficient (the oxygen pulls electron density), and the nitrogen has a lone pair. Now, you want to turn this into an amine, where the carbon is fully saturated and the nitrogen is the only functional group left. How do you get there?

The key idea: you need to add hydrogen across the $\ce{C=O}$ bond and also break the $\ce{C-N}$ bond in a controlled way, so that the nitrogen stays attached to the carbon chain. That's exactly what a strong reducing agent like lithium aluminium hydride ($\ce{LiAlH4}$) does.

The Intuition

Think of $\ce{LiAlH4}$ as a source of hydride ions ($\ce{H-}$) — tiny, negatively charged hydrogen atoms that love to attack electron-poor carbons. In an amide, the carbonyl carbon is the most electron-poor spot. The hydride attacks there first.

But here's the twist: after the first attack, the molecule rearranges. The $\ce{C=O}$ bond becomes a $\ce{C-O-}$ (an alkoxide), and the nitrogen's lone pair helps push electrons, eventually kicking out the oxygen as $\ce{OH-}$ and forming an imine intermediate ($\ce{RCH=NH}$). That imine is then attacked by another hydride, giving you the final amine.

The net result: the carbonyl carbon becomes a $\ce{CH2}$ group, and the nitrogen remains attached. No carbon atoms are lost — the amide carbon becomes the $\ce{CH2}$ next to the nitrogen.

The Precise Statement

Reduction of an amide with $\ce{LiAlH4}$ converts the $\ce{-CONH2}$ group into a $\ce{-CH2NH2}$ group, without loss of carbon atoms.

For a primary amide:

For a secondary amide ($\ce{RCONHR'}$):

For a tertiary amide ($\ce{RCONR'R''}$):

The "4[H]" represents the net addition of four hydrogen atoms — two go to the carbon, two to the nitrogen.

Why This Matters for Exams

• No carbon loss: The amide carbon becomes the $\ce{CH2}$ directly attached to nitrogen. This is a key difference from other carbonyl reductions (e.g., acid chlorides to alcohols lose carbon via $\ce{CO}$). …