Which of the following is NOT a functional group?

The correct choice is carbonates, as they do not function as traditional organic functional groups like the others listed. A functional group typically refers to a specific grouping of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.

Sulfhydryl, methyl, and amino are all established functional groups. The sulfhydryl group (-SH) is found in certain amino acids and can interact with other groups to form disulfide bonds, which are important in protein structure. The methyl group (-CH3) is associated with hydrophobic characteristics in molecules, affecting their reactivity and solubility. The amino group (-NH2) is crucial in amino acids and proteins, participating in the formation of peptide bonds.

On the other hand, carbonate typically refers to a polyatomic ion composed of carbon and oxygen (CO3^2−) and is not considered a functional group in organic chemistry. It serves more as a structural component in various inorganic compounds rather than facilitating specific chemical reactions typically associated with organic functional groups.