This work seeks to create a versatile experiment for undergraduate physical or organic chemistry students to demonstrate the role catalysis, steric hinderance and/or electron induction play in reaction rate. Catalyzed ester hydrolysis of p-nitrophenyl acetate (NPA) has long given students experience using pseudo-first order conditions to determine the rate constants for catalyzed and uncatalyzed reactions by monitoring the hydrolysis product's UV-Vis absorption. Analogs with bulky groups restricting access to the cleavage site, such as 4-nitrophenyl trimethylacetate, are compared to illustrate steric effects. Analogs with strong electron withdrawing groups, such as 4-nitrophenyl trifluoroacetate confirm inductive effects. Effectiveness of multiple catalysts are compared. Eyring plot analysis of the observed rate constant's temperature dependence gives the change in entropy, enthalpy and Gibbs free energy of the various transition states. The flexible framework allows the lab to be unique from a student perspective each term while keeping the instructor's preparation essentially identical.

Diversifying classic ester hydrolysis to illustrate catalytic, inductive, and steric effects on rate in the physical and organic chemistry laboratories

247th National Meeting (2014)

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