NMR spectrum of 3-chlorothietane, an example of complete NMR spectral analysis by computer techniques

Abstract

The NMR spectrum of 3-chlorothietane has been analyzed by the use of three computer techniques. These are (1) spectral decomposition (DECOMP), (2) spectral assignment (ASSIGN), and (3) Swalen and Reilley's iterative programs (NMEEN and NMRIT). DECOMP determines to a large extent the frequencies and intensities of all lines which make up an unresolved multiplet. ASSIGN finds all possible sets of energy levels which are consistent with the observed frequencies and intensities of the completely resolved spectrum. NMREN calculates each set of energy levels by making a least-squares fit on the assigned transition frequencies. NMRIT calculates, for each set of energy levels, the corresponding coupling constants and chemical shifts if they are real. Only one set of coupling constants and chemical shifts is consistent with the NMR spectrum of 3-chlorothietane. The chemical shifts and vicinal coupling constants are quite normal. The geminal coupling constant is -8.63 cps. There is a large long-range coupling constant across the ring of +3.12 cps. The other two long-range coupling constants are smaller and negative. The geminal and long-range coupling constants are compared with theoretical calculations.