Oxford University

2nd/3rd Year Undergraduate Experiments in Physical Chemistry
7.15 Electron Spin Resonance

Introduction || Location || Safety || Instructions

Introduction

In this experiment you will obtain and interpret the ESR spectra of some free radicals. In the first part, the hyperfine structure of the spectra caused by the unpaired electron coupling to nearby magnetic nuclei is investigated for radicals in which coupling is to hydrogen or nitrogen nuclei. These examples serve to establish the basic coupling laws which determine the appearance of ESR spectra.

In the second half the spectrum of a more substantial radical is obtained. This is interpreted using the rules established in the first part, but now the observed coupling constants are used to determine the electron densities around the ring of the aromatic radical involved. These same electron densities are calculated using Huckel molecular orbital theory, and the experimental and theoretical results compared. A brief introduction to ESR and to the experimental method is given first, and it is essential that you read this carefully before starting the experiment.

Location

Lower Teaching Laboratory, booking area.

Safety

The chemicals in this experiment need to be handled carefully. Before starting work, check the MSDS data for


Benzoquinone
Ethylene glycol dimethyl ether (1,2-dimethoxy ethane)
Potassium hydroxide
2-Propanol
Concentrated sulfuric acid
TEMPO


A comment on magnetic fields produced by the large magnet in this experiment.

Instructions

Instructions for this experiment are available for reference in a folder in the Lower Teaching Laboratory. You may obtain a personal copy from the technician in that laboratory, or download instructions (13 pages, pdf format, 191k, updated September 9, 2003).

Updated September 9, 2003.