Final answer:
The major product in the reaction of (R)-2-bromopentane with sodium cyanide in DMSO is (R)-2-cyanopentane.
Step-by-step explanation:
The reaction of (R)-2-bromopentane with sodium cyanide in DMSO will result in the formation of the major product, (R)-2-cyanopentane.
To understand why this product is formed, let's look at the reaction mechanism. In the first step of the reaction, the bromine atom in (R)-2-bromopentane is replaced by a cyanide ion from sodium cyanide. This substitution reaction is known as a nucleophilic substitution reaction.
The major product is formed when the nucleophile attacks the carbon atom that is attached to the least sterically hindered hydrogen atom. In this case, the least hindered carbon atom is the one adjacent to the bromine atom, and the least hindered hydrogen atom is the one on the same side as the bromine atom. Therefore, the cyanide ion attacks this carbon atom, resulting in the major product, (R)-2-cyanopentane.