A troublesome point in naming chemical compounds concerns the rules governing when a compound is to be written as a single word (as methylamine) or as two or more words (as methyl chloride). To solve this problem, you must determine whether the principle or parent function is an element or a compounds in its own right; if it is either one, then the name is written as a single word.

The following examples should help to clarify the system. In each name, the part of the name that denotes the parent compound 2 is italicized:

However, if the parent function cannot be constructed as being a real compound, the name is correctly written as two or more words. For example, CH3Cl could be named as a chloride, in which case we use two words, methyl chloride, to describe it. A chloride, or any halide, is a class of compound, not a specific compound. To identify a specific halide, the adjective that describes the halide is written as a separate word preceding the class name. Examples follow in which the class name is italicized.

The parent compounds designated here as amine, carbaldehyde, and sulfonic acid are properly ammonia, methanal, and sulfurous acid (HSO3H) when no substituent groups are attached. These word-separated names sometimes are called radicofunctional names.