The Dependence of Vicinal Proton-Proton Coupling Constants on Molecular Structure

Marković, Zoran; Konstantinović, S.; Gutman, Iván

doi:10.1515/zna-1994-7-815

Zeitschrift Für Naturforschung A

1994

DOI: 10.1515/zna-1994-7-815

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The Dependence of Vicinal Proton-Proton Coupling Constants on Molecular Structure

Zoran Marković

S. Konstantinović

Iván Gutman

Abstract: A modification of the Karplus equation is put forward, containing for mutually independent structural terms and four adjustable parameters. Among the new factors introduced in this modifi cation are the distance between protons and Muallay's group electronegativity, used in the evalua tion of the a-substituent effect. The new equation reproduces experimental NM R vicinal coupling constants with a standard deviation of about 0.6 Hz.

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1997

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Vicinal proton-proton coupling constants V. Couplings to methyl groups

Guilleme¹,

Fabián²

1997

Molecular Physics

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A study of the substituent e ects upon the vicinal proton± proton coupling 3 J Me to methyl groups has been carried out from data sets of experimental and calculated 3 J Me couplings in ethane, denoted 3 J 0 Me , monosubstituted ethanes, denoted 3 J X Me , and 1,1-disubstituted ethanes, denoted 3 J XY Me , with substituents of the second (C, N, O and F), third (Si, P, S and Cl), fourth (Ge, As, Se and Br) and ® fth (Sn, Sb, Te and I) rows of the periodic table. The calculations of 3 J Me couplings were performed at the self-consistent ® eld ab initio level using the 6-31G** basis set. Both the experimental and the calculated 3 J X Me couplings of monosubstituted ethanes showa quadratic (or exponential) decay with the relative electronegativity D c X of the substituents in each row. Di erent decays are found for each row suggesting a periodic behaviour for the e ect of the a atom upon 3 J X Me in addition to the dependence on D c X . The 3 J X Me couplings have been analysed using di erent re® ned equations formulated from a substituent e ect model. A data set of 33 experimental couplings is satisfactorily ® tted by two di erent re® ned equations including a quadratic dependence on D c X for the e ects of the individual substituents and a cross-term on D c X D c Y for the e ects of interaction between substituents. In the ® rst equation, with nine parameters, the periodic trends in the plots of 3 J X Me against D c X are considered by using di erent coe cients for each row in the linear term in D c X . In the second equation, with seven parameters, a unique coe cient is used for the term in D c X and the periodicity is embodied into a linear term in the relative hardness of the substituent D h X .

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Vicinal proton-proton coupling constants V. Couplings to methyl groups

Guilleme¹,

Fabián²

1997

Molecular Physics

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The Dependence of Vicinal Proton-Proton Coupling Constants on Molecular Structure

Cited by 1 publication

References 13 publications

Vicinal proton-proton coupling constants V. Couplings to methyl groups

Vicinal proton-proton coupling constants V. Couplings to methyl groups

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