P. E. Clark
and K. D. Berlin Oklahoma State University Stillwater, 74074
II
A Computer Program for Plotting NMR Spectra
O n e of the problems encountered when calculating theoretical nmr spectra is converting the numerical output into a form easily compared with the rxprrimental sprctrum. Although plotting ntutinrs urr avoilnhlc' which wint out u "stick lot" on a linr printer, we have found that in some cases, especially early in the process of refining parameters, there can be sets of lines which differ by only a few tenths of a Hz. While it is possible to plot every line using a line printer, the plot is sometimes difficult to use and frequently has little resemblance to the experimental spectrum. Since some of the lines are closely spaced, it is valuable to be able to sum these lines and plot them as their average positions. We have therefore written a set of FORTRAN IV subprograms which accept as input: (1) a calculated spectrum from LAOCN33 or NMRIT IV' and (2) a limiting parameter (XDIFF) which instructs the subroutine to sum up and average all lines which differ by less than the numerical value of the parameter. Moreover, the routine compiles a list of the line numbers (LAOCN3) or transition numbers
(NMRIT IV) which have been compressed into one line and prints them out for easy reference. A version of the program suitable for use with a Calcomp type plotter has also been written. Both programs utilize the first line at low field (the line at high field could be used as
'COOPER, J. W., "NMRIT IV Nuclear Magnetic Resonance Iteration Program," Program 126, Quantum Chemistry Program Exchange, Indiana University, 19-59, B R o ~ ~R. ~E.,~AND u ,RUSE,H. A,, J. CHEM.EDUC., 47,139 11a7n\
'DETAR,D. F., "Computer Programs for Chemistry," W. A. Benjamin, Inc., NemYork, 1968, Vol. 1, p. 10.
I
:
, 8.0
Figure 1.
loo
,
,
1.0
I
,, 6.0
5.0PPYII4.0
3.0
HZ.
Figure 3.
362
/
2.0
Experimental spectrum of pyridins (neat];
1.0
0
sweep width Figure 2.
Colcomp plob:
o, XDIFF = 0.0; b, XDIFF = 0.1; c, XDIFF = 0.2, d,XDlFF
Journal of Chemical Education
Line printer plot.;
= 0.5.
o, XDIFF = 0.0; b, XDIFF = 0.5
well) fromLAOCN3 or NMRIT IV as the starting point for the summing operation. Program listings of both programs are available from the authors. As an example of the program's utility, pyridine was selected (Fig. 1) because: (1) it has several overlapping peaks, (2) the spectral data (e.g., 6 and J values) are difficult to obtain from the experimental spectrum, to make and (3) it is ~. Of the n u m e r i d output by any other wmmon method laborious. In the sample outputs below the limiting
parameter (for final line selection) has the value of (a) 0.0,' (b) 0.5 in the line printer plots (Fig. 2) and (a) 0.0,(b) 0.1, (c) 0.2, ( d ) 0.5 in the Caloomp plots (Fig. 3). Note the changes in the plots as the value of the limiting parameter is altered. A value of 0.2 seems to give the "best" fit to the experimental spectrum. 4 In this example, the number of lines printed is governed by +,hetruncation nrocess which takes dace durina the conversion from red to in&. None of the brogram options have been utilized in producing the plot.
Volume 49, Number 5, May 1972
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