(S)-lactic acid. Computer illustration of a mole- cule of (S)-lactic acid (formula: C3H6O3). Atoms are represented as cylinders and are colour-coded: carbon (yellow), hydrogen (white) and oxygen (red). Four different groups are joined to the central carbon atom here, a property known as chirality. The groups are given priorities based on their atomic number, and the molecule is viewed along the line of the bond to the lowest priority group. The order of the other groups' decreasing priorities determines whether the isomer is classified as S (anticlockwise, as here) or R (cl- ockwise). See image A700/141 for (R)-lactic acid.