Nucleophilic aromatic substitution and benzyne

27 questions on Nucleophilic aromatic substitution and benzyne from the Organic Reaction Mechanisms III: Nucleophilic Substitution chapter: 5 NEET level, 11 JEE Main, 11 JEE Advanced. Each one opens with its answer and solution.

• Which of the following aryl chlorides reacts fastest with sodium methoxide in methanol on moderate heating, by the addition-elimination (SNAr) pathway? NEET level
• In the SNAr reaction of an activated aryl halide, the anionic intermediate in which the ring carbon bearing the halogen has become sp^3 hybridised is called NEET level
• Sanger's reagent, used to label the N-terminal amino group of a peptide, is NEET level
• Chlorobenzene is heated with aqueous NaOH at about 623 K and about 300 atm (Dow process) and the product mixture is then acidified. The main organic product is NEET level
• Which statement about benzyne (C6H4), the intermediate formed from chlorobenzene and NaNH2 in liquid ammonia, is correct? NEET level
• For 1-X-2,4-dinitrobenzenes reacting with piperidine, the reactivity order is F > Cl approx Br > I. The best explanation is that JEE Main level
• Four aryl chlorides, (I) chlorobenzene, (II) 1-chloro-4-nitrobenzene, (III) 1-chloro-2,4-dinitrobenzene and (IV) 2-chloro-1,3,5-trinitrobenzene, are treated wit... JEE Main level
• 1-Chloro-2,4-dinitrobenzene is stirred with hydrazine (H2N-NH2) in ethanol. The main product is JEE Main level
• 1-Fluoro-2,4-dinitrobenzene reacts with sodium methoxide in methanol. Which statements are correct? JEE Main level
• Assertion (A): 1-Fluoro-4-nitrobenzene reacts with sodium methoxide faster than 1-iodo-4-nitrobenzene. Reason (R): The C-F bond is weaker than the C-I bond. JEE Main level
• Chlorobenzene in which the carbon bearing chlorine (C-1) is enriched in ^14C is treated with KNH2 in liquid ammonia. Neglecting isotope effects, what fraction o... JEE Main level
• 4-Chlorotoluene is treated with NaNH2 in liquid NH3. The amine products are JEE Main level
• Which of the following aryl halides cannot give an aryne with NaNH2 in liquid NH3? JEE Main level
• Benzyne generated in the presence of furan gives, by a [4+2] cycloaddition, mainly JEE Main level
• Benzyne (C6H4) adds across the 9,10 positions of anthracene (C14H10) in a [4+2] cycloaddition. The molecular formula of the adduct (triptycene) is JEE Main level
• Match each reaction in Column I with the key intermediate in Column II. Column I: (P) 1-fluoro-4-nitrobenzene + CH3ONa; (Q) chlorobenzene + KNH2 in liquid NH3; ... JEE Main level
• 1-Chloro-2-(trifluoromethyl)benzene is treated with NaNH2 in liquid NH3. The aryne formed has its triple bond between C-1 and C-6 with the CF3 group on C-2, nex... JEE Advanced level
• 1-Chloro-2-methylbenzene (2-chlorotoluene) is treated with KNH2 in liquid NH3. Methyl exerts only a weak electronic effect on the aryne. The aminated products a... JEE Advanced level
• 3,4-Dichloronitrobenzene (1,2-dichloro-4-nitrobenzene) reacts with one equivalent of sodium methoxide in methanol on warming. The major product is JEE Advanced level
• The tripeptide Gly-Ala-Phe (glycine is the N-terminal residue) is treated with 1-fluoro-2,4-dinitrobenzene under mild basic conditions and the product is then c... JEE Advanced level
• 1-Chloro-2,4-dinitrobenzene reacts with sodium methoxide in methanol (SNAr). Which of the following changes would be expected to DECREASE the rate? JEE Advanced level
• Benzyne is generated in the presence of 2-methylfuran and trapped by a [4+2] cycloaddition across C-2 and C-5 of the furan. How does the adduct exist? JEE Advanced level
• Which of the following give 3-methoxyaniline as the main amine product when treated with NaNH2 in liquid NH3 (inductive effect of OCH3 on the aryne controls the... JEE Advanced level
• Which statements about the reaction of chlorobenzene with KNH2 in liquid NH3 and about benzyne are correct? JEE Advanced level
• Which of the following react with sodium methoxide in methanol at 25 degC by SNAr to replace the halogen with methoxy? JEE Advanced level
• Which statements about the Meisenheimer complex formed from 1-fluoro-4-nitrobenzene and methoxide are correct? JEE Advanced level
• Six aryl halides are each treated with excess NaNH2 in liquid NH3: (i) chlorobenzene, (ii) 1-chloro-4-methylbenzene, (iii) 2-chloro-1,3-dimethylbenzene, (iv) 2-... JEE Advanced level