1. Purpose

Having acquired an ¹H NMR spectrum (see Exp. 3.1) or an ¹H-coupled ¹³C NMR spectrum (see Exp. 4.11) the chemist has to extract correct chemical shifts and spin coupling constants. This task may be difficult because of higher order effects of the spin systems. In such cases a computer-aided spin simulation with following iteration may be performed.

A spin simulation starts with a set of chemical shift values and spin coupling constants taken from the experimental spectrum and from chemical experience with similar compounds. Simple simulation programs available as public-domain software for PCs are able to generate spectra which can be compared with the experimental result. For a correct solution iterative programs are required. Only if both the theoretical and the experimental spectra are identical can the evaluated chemical shifts and spin coupling constants be considered to be correct.

The LAOCOON type programs (Least squares Adjustment Of Calculated On Observed NMR spectra [2]) or the NMRIT-type programs [6], which require input and appropriate conversion of the experimental spectra, can be obtained for a variety of platforms [4]. These programs take only transition frequencies into account, and the solution can be considered to be correct if the intensities are also matched. Iterative programs [3,5] working on the full line-shape of the NMR spectrum provide the ultimate solution for the spectral evaluation. In the experiment described here we demonstrate the performance of a PC-based NMRIT-type program on ortho-dichlorobenzene.

2. Literature

H. Günther, NMR Spectroscopy, 2nd Edition, Wiley, Chichester, 1995.
S. Castellano, A. A. Bothner-By, J. Chem. Phys. 1964, 41, 3863–3869.
D. S. Stephenson, G. Binsch, J. Magn. Reson. 1980, 37, 395–408; 409–430.
K. Marat, SpinWorks version 1.3, 2002, University of Manitoba, http://www.umanitoba.ca/chemistry/nmr/nmrsource2.html
U. Weber, H. Thiele, NMR Spectroscopy: Modern Spectral Analysis, Wiley-VCH, Weinheim, 1998.
S. L. Manatt, Magn. Reson. Chem., 2002, 40, 317–330.

3. Pulse Scheme and Phase Cycle

see Experiment 3.6

4. Acquisition

perform Experiment 3.6