An acyclic unsaturated carboxylic acid 'X' reacts with I ₂ and NaHCO ₃ to give 5-(1-iodoethyl)dihydrofuran-2(3H)-one as the major product. The IUPAC name of 'X' is:

Step-by-step solution

The formation of a lactone from an unsaturated carboxylic acid using I ₂ and NaHCO ₃ proceeds via an iodolactonization reaction. The product is a five-membered -lactone (dihydrofuran-2(3H)-one) with a 1-iodoethyl group at the 5-position. In the lactone ring, the oxygen is bonded to what was the carbonyl carbon (C1) and the -carbon (C4) of the original acid. This indicates that the nucleophilic attack of the carboxylate occurred at C4, which means the original double bond was between C4 and C5. The substituent at th