Consider the following reaction sequence: 1,4-Dibromobutane NaCN (1 equivalent) P NaNH ₂ Q H ₂/ Ni R The major product R is

Step-by-step solution

Step (i): 1,4-dibromobutane reacts with 1 equivalent of NaCN to undergo mono-substitution (S _N 2), yielding 5-bromopentanenitrile (P). Step (ii): The strong base NaNH ₂ deprotonates the acidic -carbon (C2) of the nitrile, forming a carbanion. This carbanion undergoes an intramolecular S _N 2 attack on C5, displacing the bromide ion. The newly formed ring contains four carbon atoms (C2, C3, C4, and C5), resulting in cyclobutanecarbonitrile (Q). Step (iii): Catalytic hydrogenation (H ₂ /Ni) reduces the nitrile group