CORN law

The CORN law is the rule that allows to distinquish enantiomers from each other. In other word, it determines whether the amino acid is a L-isomer or D-isomer. All amino acids have the same core and differ due to their side chain. There are four different group attached to α-carbon, making α-amino acids chiral. These groups are: carboxylic acid group (-COO^-), amino group (-NH₂), a hydrogen atom and a distinctive R group (representation of side chain).

The CORN is an acronym for -COOH , the -R  and -NH₂ groups. If the carboxyl group is followed by the R group and the amino group in clockwise direction, then the amino acid is a L-isomer. If the movement is in the anticlockwise direction, the amino acid is a D-isomer^[1].

References:

1.Jeremy M. Berg, John L. Tymoczko, Lubert Stryer. Biochemsitry. 7th. ed. New York: WH Freeman and Company. 2011.