What is the prefix for a four-carbon chain alkyl group?

The prefix for a four-carbon chain alkyl group is "but-." In organic chemistry, the prefixes indicate the number of carbon atoms present in an alkyl group.

For a four-carbon alkyl chain, the name comes from the root "butane," which is the simplest saturated hydrocarbon with four carbon atoms. Therefore, when referring to the alkyl group derived from butane, it is designated as "but-," such as in "butyl" groups.

In contrast, "hex-" indicates a six-carbon chain, "pent-" signifies a five-carbon chain, and "oct-" represents an eight-carbon chain. Thus, the correct prefix for a four-carbon alkyl group is "but-," aligning with the naming conventions established for organic compounds.