Question

Megatomoic acid, the sex attractant of the female black carpet beetle, has the following structure. CCCCCCCCC=CC=CCC(=O)O (a) What is its IUPAC name? (b) State the number of stereoisomers possible for this compound.

Short answer

Answer: The IUPAC name of the compound is 9,11-dodecadienoic acid, and it has 4 possible stereoisomers.

Step-by-step solution

(Step 1: Identify the longest carbon chain and main functional group)

The main functional group in the given structure is the carboxylic acid group (-COOH). We start by identifying the longest continuous carbon chain that includes the carbon of the carboxylic acid group. In this case, the longest carbon chain has 12 carbon atoms.

(Step 2: Number the carbon atoms in the chain)

We want to number the carbon atoms in a way that results in the lowest possible numbers for the functional groups and substituents. We start from the carbon of the carboxylic acid group by numbering it as 1, and move towards the other end of the chain. In this case, we have double bonds at positions 9 and 11.

(Step 3: Name the compound using IUPAC rules)

Based on IUPAC nomenclature, we construct the name of the compound as follows: a) Mention the number of carbon atoms in the longest chain with proper prefix, in this case, "dodec" for 12 carbons. b) Indicate the position of the double bonds and the suffix "ene" for the presence of double bond(s), "9,11-diene" in this case. c) Add the suffix "oic acid" to denote the presence of the carboxylic acid group. Putting it all together, the IUPAC name for the compound will be: "9,11-dodecadienoic acid". Answer (a): The IUPAC name of the compound is 9,11-dodecadienoic acid.

(Step 4: Identify chiral centers and geometric isomers)

Now, we will determine the number of stereoisomers for this compound. There are no chiral centers in this molecule. However, there are two double bonds, and each one could possibly have cis/trans isomers (also known as E/Z isomers).

(Step 5: Calculate the number of stereoisomers)

Since each of the two double bonds can have two possible configurations (cis or trans), we have a total of 2^2 = 4 possible stereoisomers for this compound. Answer (b): There are 4 possible stereoisomers for this compound.