Question

Explain why cyanogens bromide does not cleave on the C-side of cysteine.

Short answer

The answer is

Imine is not formed due to the difficulty in the formation of the strained four-membered ring.

Step-by-step solution

Step-by-Step Solution Step 1: Cysteine

The amino acids are the simple basic units of peptides and proteins. Cysteine is an amino acid containing a sulfur atom.

Explanations

The structure of cysteine is given below.

Cysteine can react with cyanogens bromide, and the sulfur will not be positively charged, hence a poor leaving group. In addition, the lactone will not be formed as it would have a strained four-membered ring. The imine will not be formed without lactone formation, and therefore, the cleavage cannot occur.