Esterification (shown below) is a reaction converting a carboxylic acid to its ester, It involves only the carbonyl carbon. Esterification of (-) lactic acid with methanol yields (+) methyl lactate. Assuming that there are no side reactions, what is true about this reaction?

An  $S_{N^1}$ reaction at the chiral center has inverted the optical rotation

Optical rotation is not directly related to absolute configuration, so the change in sign of rotation is merely a coincidence

An $S_{N^2}$ process has occurred, inverting the absolute configuration of the chiral center

A diastereomer has been produced; diastereomers have different physical properties including optical rotation