The Fischer esterification reaction synthesizes an ester via a nucleophilic acyl substitution reaction. The stereochemistry of the alcohol group is unchanged as it is the alcohol oxygen that makes the nucleophilic attack. The Mitsunobu reaction, on the other hand, allows the synthesis of an ester in which the stereochemistry of the alcohol is inverted. The reaction involves a carboxylic acid and an alcohol, as well as triphenylphosphine and an azo compound termed diethyl azodicarboxylate (DEAD). As with the Fischer esterification, H2O is formally lost during the reaction. However, in the Mitsunobu reaction the OH is lost from the alcohol and the H is lost from the carboxylic acid. The overall reaction is an SN2 reaction which occurs with inversion of configuration at the chiral carbon. Draw curved arrows to show the movement of electrons in this step of the mechanism.