The major product of the following reaction is:

1. Partial Reduction: DIBAL-H is a bulky, sterically hindered reducing agent. At low temperatures, it delivers exactly one equivalent of hydride ($$\text{H}^-$$) to the electrophilic carbon of the nitrile group ($$\text{R--C}\equiv\text{N}$$). This reduces the triple bond to a double bond, stopping cleanly at an imine intermediate ($$\text{R--CH}=\text{NH}$$).
2. Hydrolysis: When water ($$\text{H}_2\text{O}$$) is introduced during the workup step, the imine intermediate undergoes rapid nucleophilic hydrolysis, replacing the nitrogenous group with an oxygen atom to yield an aldehyde ($$\text{R--CH}=\text{O}$$).

Detailed Evaluation of Each Option:

• Option A: $$\text{RCOOH}$$ (Carboxylic Acid)

  This statement is incorrect. Nitriles can be hydrolyzed to carboxylic acids using strong aqueous acids or bases with prolonged heating, but a hydride reduction with DIBAL-H does not oxidize the carbon to an acid state.




• Option B: $$\text{RCHO}$$ (Aldehyde)

  This statement is correct. The primary synthetic application of treating a nitrile with DIBAL-H followed by water is the controlled, selective conversion into an aldehyde.




• Option C: $$\text{RCH}_2\text{NH}_2$$ (Primary Amine)

  This statement is incorrect. Complete reduction down to a primary amine requires a much stronger, unhindered reducing agent like lithium aluminum hydride ($$\text{LiAlH}_4$$) or catalytic hydrogenation ($$\text{H}_2/\text{Pd}$$).




• Option D: $$\text{RCONH}_2$$ (Primary Amide)

  This statement is incorrect. An amide is formed during the partial chemical hydrolysis of a nitrile group, not through a hydride reduction pathway.

Conclusion:

DIBAL-H reduces nitriles selectively to imines, which yield aldehydes upon subsequent aqueous workup.

Answer: Option B — $$\text{RCHO}$$