Methyl group?
Yeah, the "R." "R" is the standard shorthand for any CH
n chain. Methyl, -CH
3, is the shortest one. The next one up is "ethyl," -C
2H
5, then "propyl," then "butyl," and so on. IIRC, these are called "aliphatics," and with many Cs, an "aliphatic chain," but yer talkin' 65+ year old memory from this old coot.
Terry