What is peptide linkage?(ii) Write general characteristics of interhalogen compounds.

Answer:

(i) Peptide linkage: The amide linkage –CO–NH– formed between the –COOH group of one α-amino acid and the –NH₂ group of another, with the loss of a water molecule, is called a peptide linkage (peptide bond). Example: glycine + alanine → H₂N–CH₂–CO–NH–CH(CH₃)–COOH (glycylalanine) + H₂O. Proteins are polypeptides held together by such linkages.

(ii) General characteristics of interhalogen compounds (XX′_n, n = 1, 3, 5, 7; X is the larger, less electronegative halogen):

1. They are covalent molecules and are diamagnetic.
2. They are volatile solids or liquids at 298 K, except ClF, which is a gas.
3. They are more reactive than the halogens (except fluorine), because the X–X′ bond is weaker than the X–X bond.
4. They are hydrolysed by water, giving a halide ion (from the smaller halogen) and an oxyhalide ion (from the larger halogen), e.g. ICl + H₂O → HCl + HOI.
5. Their structures follow VSEPR theory (e.g. ClF₃ T-shaped, BrF₅ square pyramidal, IF₇ pentagonal bipyramidal).