In organic chemistry, the letter "R" is used to represent any group of carbon or hydrogen atoms that is attached to the rest of the molecule_Structures_(aka_R_Groups)). It is often used to designate part of a molecule outside of the region of interest, and represents the "Rest of the Molecule"Structures(aka_R_Groups)). The R group is a convenient way to abbreviate the structures of large biological molecules, especially when we are interested in something that is occurring specifically at one location on the molecule_Structures_(aka_R_Groups)). It is important to note that R should not be confused with R (the gas constant), R (the one-letter abbreviation for the amino acid arginine) or R (a designation of absolute configuration) .