E. Lustig

Least-Squares Fitting

When a set of experimental values m, corresponding to a set of theoretical values M, has been measured, and the functional dependence of the l values M on the q parameters p. that is,

A 1H, 13C, and 15N NMR spectral analysis of 15N-nitrobenzene

{{M}_{k}} = {{f}_{k}}({{p}_{1}},{{p}_{2}}, \ldots ,{{p}_{q}}),

Application of Low‐Field NMR to the Unambiguous Assignment of Spin‐Coupling Parameters. III. Other Pentafluorobenzenes

(X.1) is known, a method remains to be devised to obtain the p’s from the m’s.

Proton spin coupling in four-membered rings—I. 2:2-d2-oxetane

The complete high-precision spectral analyses; of the per-12C and the naturally abundant 13C isotopomers of the compounds in the series C6HnF6−n, where n = 0 to 6, are presented. Linear regression analyses of the JCH, JCF and one-bond fluorine secondary isotope shift data show that substituent effects upon these parameters are additive. INDO-SCF MO calculations of all the JFF, JFH, JCH and JCF values in this series of compound were performed and the results were compared with the experimental data. These calculations reproduce the signs, trends, and magnitudes of the couplings, although they become progressively poorer along the above series of coupling constants. Possible sources of error in the theoretical approach are discussed.

The complete analysis of the 19F spectrum of pentafluorobenzenes. A general solution of the AA′XX′Z case

Abstract Iterative analysis of the 1 H, 13 C, and 15 N NMR spectra of 15 N-nitrobenzene yielded accurate values for all 1 H 1 H, 13 C 1 H, 15 N 1 H, and 15 N 13 C coupling constants; their signs were determined partly from the spectral analysis and partly by heteronuclear double-resonance experiments. INDO MO calculations of values of J HH , J NH , and J NC for nitrobenzene and aniline reproduced, in a qualitative manner, the trends in the values of J found, although the magnitudes of J NH and J NC and the effects of replacement of NO 2 by NH 2 were overestimated. Inclusion of orbital and spin-dipolar contributions to J NC did not improve the correlations.

Basic Computer Methods

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Diagonalization of Symmetric Matrices

The 6.14‐MHz fluorine NMR spectra were employed in removing ambiguities in the signs and assignments of coupling constants in C6F5–Cl, –Br, –CN, –COOH, –COCl, –OH, –NH2, and –SO2Cl. Except for C6H5OH, selection of the correct parameter set entailed only a visual comparison of the low‐field spectrum and computed spectra based on permutations of the nonassignable parameters from high‐field studies. The correct parameter sets were subsequently computer refined to obtain best fits to the 6.14‐MHz spectra. However, in the case of C6F5OH, the solvent dependence of the spectrum necessitated computer iterative analysis of the 6.14‐MHz data to arrive at the correct parameter set. For C6F5COCl, high‐precision 94.1‐MHz spectra were of use in eliminating all but one uncertainty in the assignments. The Abraham–MacDonald–Pepper linear relationship involving the ortho–ortho substituent contribution and the Hammett σp constant was modified and extended to yield for the compounds C6F5–X the relationship J26(Hz) = − 9.5σp(...

The Calculation of an NMR Spectrum

Abstract Proton spin coupling constants for unsubstituted four-membered heterocyclics are unknown, and unravelling of their complex A 2 B 4 -type spectra is possible only with the aid of weak double irradiation. Thus, 2:2- d 2 -oxetane was synthesized and all accessible NMR parameters were obtained from an analysis of the 4-proton band. Geminal coupling constants are in accord with predictions of the Pople and Bothner-By theory, and diagonal coupling constants are smaller than 0·3 Hz.