In these latter cases the reaction may proceed in different directions; thus, with the aromatic hydrocarbons, chlorine in the cold or in the presence of a carrier substitutes in the benzene nucleus, but in the presence of sunlight or on warming, substitution takes place in the side chain.
Blom found that on brominating orthoacetamido-acetophenone in presence of water or acetic acid, the bromine goes into the benzene nucleus, whilst in chloroform or sulphuric acid or by use of bromine vapour it goes into the side chain as well.
If methyl benzene is reacted with chlorine in the presence of uv light, substitution takes place in the alkyl side chain.
Once activated caspases act as cysteine proteases, using a cysteine side chain for catalyzing peptide bond cleavage at aspartyl residues in their substrates.
The small hydrogen side chain of the glycine amino acids permits the backbone torsion angles to adopt unusual conformations.
