Answer: It undergoes intramolecular cyclisation forming a highly reactive sulfonium ion (ethylenesulfonium) that acts as an alkylating agent via SN1.
- A It undergoes intramolecular cyclisation forming a highly reactive sulfonium ion (ethylenesulfonium) that acts as an alkylating agent via SN1
- B It is generally a strong Bronsted acid that directly protonates the nucleophilic nitrogen atoms found within DNA bases as frequently observed in practice
- C It rapidly eliminates hydrochloric acid to generate a reactive vinyl sulfide intermediate that then attacks DNA in many documented cases
- D It reacts with the DNA backbone through an largely sulfur-centred free radical chain propagation mechanism according to conventional understanding
Correct answer: A. It undergoes intramolecular cyclisation forming a highly reactive sulfonium ion (ethylenesulfonium) that acts as an alkylating agent via SN1
Explanation: The sulfur in mustard gas undergoes intramolecular SN2 cyclisation, forming a reactive 3-membered ring sulfonium ion (episulfonium); this carbocation equivalent alkylates nucleophilic N-7 of guanine, crosslinking DNA.
SN2 proceeds in a single step with backside attack and inversion of configuration, while SN1 forms a planar carbocation intermediate first, leading to racemisation.
Concept context
Study carbon-halogen compounds: how they are made, how they react via SN1/SN2 and elimination, their stereochemistry, and their environmental impact.