Computerized Calculation of Trial Parameters for an AA'XX' System The procedure for calculating detailed nmr spectra for a given set of parameters (chemical shifts and coupling constants) is well e~tablished.'.~Except for the simplest eases, it is a laborious procedure best done using a computer.3.4 One of the computer programs most frequently used to construct theoretical nmr spectra is LOACOON Ill Program3 For an AA'XX' system, the LOACOON III Program uses six parameters, two chemical shifts, and four coupling constants to construct the theoretical spectrum. These six trial parameters are calculated based on the assignment of the observed line frequencies in the experimental spectrum. However, calculating the parameters is a tedious procedure, and it is often necessary to obtain several sets of trial parameters based on reassignment of the observed lines in the experimental spectrum. A computer program has been written to calculate these trial parameters (the trial chemical shifts and coupling constants) based on the experimental line frequencies using the equations given in Abrahams These equations lead to the parameters, K, L, M, and N, which are in turn used to calculate the trial chemical shifts and coupling constants. In addition, the program is able to compute trial parameters based on trial K , L, M and N values alone. For each set of K, L, M and N values the program will compute 32 sets of trial parameters. The program gives a printout as well as a punched output which can be used directly as the data input for the LOACOON I11 Program. The program with a sample printout is available upon request.
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Pople, J. A., Schneider, W. G., and Berstein, H. J., "High Resolution Nuclear Magnetic Resonance," McGraw-Hill Bwk Company, New York, 1959, p. 142. Emsley, J. W., Feeney, J., and Sutcliffe, L. H., "High Resolution Nuclear Magnetic Resonance Spectroscopy," Pereamon Press. New York. 1965.~ Vol. ~ 1. o.399. ~~, ~ , ~ a s t e l l a ks., and Bothner-By, A. A,, J Chem. Phyi., 41,3863 (1964). Swalan, J . D., and Reilly, C. A., J Chem. Phys., 37, (1961). "braham. R. J., "Analysis of High Resolution NMR Spectra," Elsevier Publishing Company, New York, 1971, p 86. Federal City College Washington, D.C. 20001
George Ng
Volume 52, Number 2. February 1975
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