Question

What does the R stand for in functional groups?

Answer 1

When we are not referring to optical isomerism, `R` in a formula refers to an alkyl residue, `C_nH_(2n+1)`.

Explanation:

When we write `RC(=O)H` or `RCH=CHR`, or `R_3C-X`, clearly we highlight the functional group of interest: aldehyde; olefin; halide etc. Why do we do this? Well, because the interesting chemistry is going to occur at that functional group.

The `R` substituent, of general formula `C_nH_(2n+1)` is along for the ride, and is tacked on to the end of the chain.