Question

What is the best name for this molecule? Explain your naming process.

A hydrocarbon with seven total carbons single bonded together. There is a straight chain of five carbons across the bottom with one ethyl group (two carbons) branching off of the third carbon.

Answer 1

According to the IUPAC nomenclature rules, you first need to identify the longest chain of carbon atoms in the molecule, which will serve as the parent chain. Here, the longest chain contains 5 carbons single-bonded together, so the parent chain is pentane.

Next we look at substituents. Substituents are named in two parts: 1) a number, indicating which carbon atom of the parent chain it is attached to, and 2) a word, indicating the number of carbons in the substituent. Here, there is an ethyl group branching off the 3rd carbon, in other words a 3-ethyl.

Putting it all together, we have 3-ethylpentane!