Trichloromethyl group

The trichloromethyl group is a functional group that has the formula –CCl3. The naming of is group is derived from the methyl group (which has the formula –CH3), by replacing each hydrogen atom by a chlorine atom. Compounds with this group are a subclass of the organochlorines. Some notable examples of compounds with this group are trichloromethane H–, 1,1,1-trichloroethane –, and chloral –.

The trichloromethyl group has a significant electronegativity. For this reason, trichloromethyl-substituted acids, such as trichloromethanesulfonic acid, are often stronger than the original. For example, the acidity constant (pKa) of trichloroacetic acid – is 0.77, whereas that of acetic acid is 4.76.

By the same principle, the trichloromethyl group generally lowers the basicity of organic compounds, e.g. trichloroethanol.