Six aryl halides are each treated with excess $NaNH X_{2}$ in liquid $NH X_{3}$ : (i) chlorobenzene, (ii) 1-chloro-4-methylbenzene, (iii) 2-chloro-1,3-dimethylbenzene, (iv) 2-bromo-1,3,5-trimethylbenzene, (v) 1-bromo-3-methoxybenzene, (vi) 1-bromo-2,6-diethylbenzene. Assume that an aryne forms whenever the halogen has at least one ortho hydrogen. How many of the six react by the elimination-addition (benzyne) mechanism? Give your answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 3

An aryne can form only if a hydrogen is present on a ring carbon next to the carbon bearing the halogen. Substrates (i), (ii) and (v) have ortho hydrogens. In (iii), (iv) and (vi) both ortho positions carry alkyl groups, so no aryne can be formed. The count is 3.

Practice Organic Reaction Mechanisms III: Nucleophilic Substitution More on Nucleophilic aromatic substitution and benzyne

Previous questionNext question

Answer: 3

More questions on Nucleophilic aromatic substitution and benzyne