# Why is an alkyl group is denoted by "R"?

Jul 13, 2018

It originally was used as an abbreviation of the word "Radical"......but it is not only used for alkyl groups....

#### Explanation:

Historically, the word "radical" was used to refer to a part or portion of a complete molecule. It is less commonly used today, except in the case of "free radical" which is effectively a species formed from "part of a molecule" that has a free unpaired election.

However, the abbreviation R has stuck.

But R does not only denote an alkyl group. When you see something like $R - C {O}_{2} H$ it means "any group in which a carbon or hydrogen atom is attached to the rest of the molecule."

So R could be an alkyl group, but not necessarily.