In proteins, side chains are attached to the alpha carbon atoms of the amino acid backbone.)
The phrases most-substituted and least-substituted are frequently used to describe or compare molecules that are products of a chemical reaction.
[citation needed] According to the above rules, a carbon atom in a molecule, considered as a substituent, has the following names depending on the number of hydrogens bound to it, and the type of bonds formed with the remainder of the molecule: In a chemical structural formula, an organic substituent such as methyl, ethyl, or aryl can be written as R (or R1, R2, etc.)
It is a generic placeholder, the R derived from radical or rest, which may replace any portion of the formula as the author finds convenient.
[9][10] One cheminformatics study identified 849,574 unique substituents up to 12 non-hydrogen atoms large and containing only carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus, selenium, and the halogens in a set of 3,043,941 molecules.
[11] An infinite number of substituents can be obtained simply by increasing carbon chain length.