Concept explainers
a)
Interpretation:
The first step of the reaction shown involves the nucleophilic substitution of the S atom on the methionine side chain with BrCN to give cyanosulfonium ion [R2SCN]+. The structure of the product formed is to be given and a mechanism for its formation is to be proposed.
Concept introduction:
S atom has two unshared pair of electrons. The nucleophilic attack of an unshared pair of electron present in S on the C of BrCN will displace the bromide ion to yield cyanosulfonium ion. It is a nucleophilic substitution reaction.
To give:
The structure of the product formed in the first step of the reaction shown which involves the nucleophilic substitution of the S atom on the methionine side chain with BrCN to give cyanosulfonium ion [R2SCN]+ along with the mechanism of its formation.
b)
Interpretation:
The second step of the reaction shown is an internal SN2 reaction, in which the carbonyl oxygen of methionine residue displaces the positively charged sulfur group to form a five membered ring product. The structure of the product formed is to be given and a mechanism for its formation is to be proposed.
Concept introduction:
The internal nucleophilc attack of the unshared pair of electrons on the sulfonium ion can lead to the formation of a five membered ring product.
To give:
The structure of the product formed in the second step of the reaction shown which is an internal SN2 reaction, in which the carbonyl oxygen of methionine residue displaces the positively charged sulfur group to form a five membered ring product and a mechanism for its formation.
c)
Interpretation:
The third step of the reaction given is a hydrolysis reaction to split the peptide chain to yield a lactone. The structure of the lactone ring formed is to be given and a mechanism for its formation is to be proposed.
Concept introduction:
The imine derivative (CH=NH) when hydrolyzed with aqueous acids breaks to give a carbonyl compound and an amino derivative as products.
To give:
The structure of the lactone ring formed during the hydrolysis of the peptide chain and a mechanism for its formation.
d)
Interpretation:
The final step of the reaction given is a hydrolysis of the lactone to give the product. A mechanism for this hydrolysis reaction is to be proposed.
Concept introduction:
Lactones upon hydrolysis give hydroxy acids as products.
To propose:
A mechanism for the hydrolysis of the lactone to give the product.
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Organic Chemistry
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