Isobutylene Dimerization: A Discovery-Based Exploration of Mechanism and Regioselectivity by NMR Spectroscopy and Molecular Modeling

MariahL. Schuster, Karl P. Peterson, Stacey A. Stoffregen

Index: 10.1021/acs.jchemed.7b00453

Full Text: HTML

Abstract

This two-period undergraduate laboratory experiment involves the synthesis of a mixture of isomeric unknowns, isolation of the mixture by means of distillation, and characterization of the two products primarily by NMR spectroscopy (1D and 2D) supported with IR spectroscopy and GC–MS techniques. Subsequent calculation and examination of the relative energies of the products and of the lowest unoccupied molecular orbital of the products’ common cationic intermediate provide a means of understanding the unique regioselectivity of the reaction. The combination of spectroscopic, spectrometric, and molecular modeling data obtained by students allows them not only to identify the products and propose a reasonable stepwise mechanism for the reaction, but also to rationalize why the non-Zaitsev product predominates.