What characterizes the thiol functional group?

The thiol functional group is characterized by the presence of a sulfur atom bonded to a hydrogen atom, resulting in the chemical structure R–SH, where R is an organic group. In the context of the given choices, the correct representation of a thiol is found in the option that displays the structure CH3-SH. Here, the methyl group (CH3-) is linked to a sulfhydryl group (-SH), illustrating the defining feature of thiols.

Thiol groups are significant in biochemistry because they can participate in redox reactions and play an essential role in the structure and function of many proteins, particularly through the formation of disulfide bonds that help stabilize protein structures. This makes the sulfur atom in the thiol particularly important in biological systems.

The other options represent different functional groups entirely. For instance, CH3-OH is an alcohol, characterized by the hydroxyl functional group (-OH). H3C-COOH represents a carboxylic acid, which contains a carbonyl group (C=O) and a hydroxyl group (-OH) connected to the same carbon. H3C-CHO depicts an aldehyde with a carbonyl group (C=O) bonded to a hydrogen atom and a carbon group