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The “Alpha Carbon” Is The Carbon Adjacent To The Carbonyl The functional group C=O is called a “carbonyl”. The carbon itself is called the “carbonyl carbon”, and the oxygen is called “the carbonyl oxygen”. But what do you call a carbon adjacent to the carbonyl carbon… or 3 carbons away? In organic chemistry, it’s common to use Greek letters to denote this. So the carbon adjacent to a carbonyl is called an “α (alpha) carbon”, two carbons away is called a “β carbon”, and so on. This nomenclature can be used to depict different kinds of substituted carbonyl groups. For example a ketone with an OH on the beta carbon would be called a “β-hydroxy ketone”. If it was one carbon further down it would be a “γ hydroxy ketone”. If we have a double bond between the α carbon and the β carbon it’s common to call it “α,β-unsaturated”. So we can have α,β unsaturated ketones, aldehydes, esters, and so on. It can keep going beyond gamma, of course, but it’s rare to see it progress beyond ε (epsilon). Another thing: aldehydes, esters, carboxylic acids, and so on, can only have one “alpha” carbon each, wheras ketones can have two. Sometimes you’ll see one set of Greek symbols marked with ‘ (prime) symbols to distinguish them. The location of the prime is completely arbitrary. For esters, the OR group is not denoted “alpha”. It’s usually just called the “alkoxy” group. Amino acids (except for glycine) have a chiral carbon atom adjacent to the carboxyl group (CO2-). This chiral center allows for stereoisomerism. The amino acids form two stereoisomers that are mirror images of each other. The structures are not superimposable on each other, much like your left and right hands. These mirror images are termed enantiomers. #aminoAcid #carbonNaming #chiralCenters #proteins #peptide #polypeptide
