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Vicinal Fluorine–Proton Coupling Constants: II. Individual Substituent Effects

✍ Scribed by J. San Fabián; J. Guilleme; E. Dı́ez

Publisher
Elsevier Science
Year
1998
Tongue
English
Weight
190 KB
Volume
133
Category
Article
ISSN
1090-7807

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✦ Synopsis

The angular dependence and the effect of individual substituents upon the NMR vicinal fluorine-proton couplings 3 J FH have been studied using data sets of experimental and calculated couplings. Coupling constants for a series of fluoroethane derivatives, CHXF-CH 3 and CH 2 F-CH 2 X (X ‫؍‬ CH 3 , NH 2 , OH, and F), were calculated by means of the SCF ab initio and semiempirical INDO/FPT methods. The calculated couplings reproduce correctly the main experimental trends in spite of the limitation in the calculation because of lack of electronic correlation and the use of medium size basis set. The individual substituent effects ⌬K ni Xi are described by quadratic expressions on the relative electronegativities of substituents

2 ). A selected data set of 58 experimental couplings, ranging from 1.9 to 44.4 Hz, has been collected from the literature. An extended Karplus equation with 16 coefficients that includes the electronegativity substituent effects has been derived from the experimental data set with a root-mean-square deviation of 1.2 Hz.

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