Threonine is a standard amino acid with a polar side chain. A structural formula shows an amino acid. The carboxyl group, C O O (minus), is at the top. The alpha carbon is labeled A and is attached to the C O O (minus) group, an N H 3 (plus) group, an H atom, and the side chain. The side chain formula is C H (O H), C H 3. The first carbon of the side chain is labeled B. Carbon B is attached to carbon A, an O H group, an H atom, and a C H 3 group. The second carbon of the side chain is labeled C. Carbon C is attached to three H atoms. Identify the chiral centers in threonine. carbon a carbon c carbon b the carboxyl carbon the amino nitrogen How many optical isomers does threonine have? 1 3 8 4 2 To determine whether the configuration of a chiral center is R or S, you must assign priorities to the groups around the center. The groups around carbon b are CH3, H, OH, and C(H)(NH+3)(COO−). What is the highest‑priority group? −C(H)(NH+3)(COO−) −CH3 −H −OH What is the second‑highest priority group? −OH −H −C(H)(NH+3)(COO−) −CH3