The Energy Profile for Rotation about the C-C Bond in Substituted Ethanes: A Multi-Part Experimental Computational Project for the Physical Chemistry Laboratory

Abstract

This paper describes a multi-part project for the physical chemistry lab that includes both experimental and computational approaches to the investigation of the energy profile for internal rotation in substituted ethanes. Experimental approaches include dipole moment determinations, high-resolution nmr spectroscopy (including coupling constant determinations from the analysis of C-13 satellites), and infrared spectral analysis, all directed toward the goal of determining the relative populations - and thereby the relative energies - of low energy rotamers of a substituted ethane as a function of substituent, temperature and solvent composition. These analyses are in turn compared with the results of theoretical calculations involving both molecular mechanics and quantum mechanics, including both semi-empirical and ab initio methods. The whole project takes 4-5 lab periods and provides a good example of the close interaction between theory and experiment that is typical of research in physical chemistry.See Letter re: this article.