Calculations of chemical shifts

Abstract

Electric field theory is used to predict the 1H, laC and 19F chemical shifts of a series of halogenated ethanes and the lUF shifts of some cyclobutanes. The quantity 3PI/r 6 is used to describe the time-averaged square of the electric field at the nucleus from fluctuating point-dipoles elsewhere in the molecule. The results are compared with predictions made by an alternative method, using P/Ir a , to define the electric fields. The calculations show that, whatever the theoretical justification or lack of it, the former quantity is often more widely applicable than the latter.

The 19F NMR spectrum of cis‐1,2‐dichlorohexafluorocyclobutane

“…The chemical shifts have been adequately explained by Feeney et al 8 The value of ,J(FF) for 1 lies within the range found for other fluorinated cyclobutanes and little more can be said due to the paucity of data. It is, however, noteworthy that 2J(FF) for 1 is c. 30 Hz larger than that for 1,1,2,2-tetrachlorotetrafluorocyclobutane (3) (3), indicating a strong influence from substituents p to the CF, group; this appears to be part of a general trend11.12 for electronegative substituents to increase ,J(FF).…”

A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes

“…It may be as compared to the C-C bond length (1.52 A) noted that these shifts may be another example in toluene. of the so-called heavy-atom perturbations, for 4~0 H , S i H is markedly smaller in magnitude than which numerous and probably related explana-is 4~0 H , C H 3 in toluene, indicating that a positive o tions have been advanced (18)(19)(20) The other couplings between the ring protons in Table 1, when compared with the benzene coupling parameters and with those for toluene, are consistent with a relatively weak perturbation of the electrons in the phenyl group. For example, in phenylsilane all these coupling constants equal those in benzene to within experimental error.…”

Proton and fluorine magnetic resonance studies of some benzoyl fluoride derivatives. Sensitivity of the fluorine shifts to intramolecular van der Waals interactions and steric effects

“…The manual oscillator in this spectrometer was replaced by an external HP 4204A audiooscillator and either the high-field (for ring fluorines) or the low-field (for COF) sidebands of CF3CC13 were used as lock signals. The resonance of internal CFCI3 occurs at 82.2 ppm to low-field of CF3CC13 (14).…”

“…Fluorination of the commercial benzoic acid derivatives with SF, (13) yielded the corresponding benzoyl fluorides (13,14). Product identity was confirmed by mass, 'H, and 19F spectra and by analysis (A. Bernhardt) for C, H, and F in 2, 3, and 4 which, respectively, had mp 30°C, bp 45"C/0.5 Torr, and bp 64"C/2 Torr; 5 had bp 35"C/5 Torr.…”