What is the IUPAC name for an unsaturated 8-carbon fatty acid with a double bond between carbons 9 and 10?

The correct answer is based on the conventions established by the IUPAC nomenclature system for fatty acids, particularly concerning the identification and naming of unsaturated fatty acids. In this case, we have an 8-carbon fatty acid with a double bond specifically located between the 9th and 10th carbon atoms in the chain.

The IUPAC naming convention dictates that the source of the carbon chain is numbered starting from the carboxylic acid functional group (the -COOH part of the fatty acid). Therefore, in an 8-carbon chain, the carbon atoms are counted from the carboxylic acid end, which makes the first carbon the one attached to the -COOH group.

Given that the double bond occurs between carbon 9 and carbon 10, this means that the first carbon in the numbering system corresponds to the carboxylic acid carbon (carbon 1), and the tenth carbon in this sequence is the one before the double bond. This gives the correct position of the double bond as indicated in the name "oct-9-enoic," where "enoic" signifies the presence of a double bond and "oct" signifies an eight-carbon chain.

This rationale allows for the correct identification of the bond position