George Slomp

NMR Spectrum of the Ethyl Group. An Exact Solution

An exact solution of the spin Hamiltonian for the ethyl group has been calculated and the results have been compared with the experimental NMR spectra of ethyl sulfide and tetraethylsilane. For ethyl sulfide it was found that δH0=52.8±0.4 cycles at 40 Mc and J=7.42±0.05 cycles. For tetraethylsilane, δH0=—16.9±0.4 cycles at 40 Mc and J=7.9±0.2 cycles.

Analysis of ABX Spectra in NMR Spectroscopy

Abstract ABX spectra are produced by a special type of three-spin system in which two nonequivalent nuclei are strongly coupled and each is weakly coupled to a third nonequivalent nucleus. The strength of the coupling is determined by J/Δ; the magnitude of the coupling constant relative to the difference between the chemical shifts of the nuclei, expressed in hertz. Although spectral changes are continuous as the strength of the coupling varies, spectra in general become quite abnormal at about J/Δ = 0.15, and this is therefore taken as the boundary between strong and weak coupling. (The exact boundary defined by different investigators varies somewhat, but this is not important.) Bernstein et al. [l] have given the notation ABX to this system, indicating with letters of the alphabet the strength of the coupling. Adjacent letters in the alphabet represent strongly coupled nuclei having different chemical shifts and remote letters represent weakly coupled nuclei. Magnetically equivalent nuclei have identic...

A new approach to 16α-halo corticoids. III. Configuration of 16-substituted-17(20)-pregnene adducts by nuclear magnetic resonance spectroscopy

Abstract Examination of the position and pattern of C-16 proton magnetic resonance signals provides an excellent method for distinguishing each of the four possible isomers of C-16 substituted pregn-17(20)-ene-21-oic acid methyl esters and C-16 substituted pregn-17(20)-ene-21-acetates.

1,1,3-Tricyano-2-amino-1-propene (U-9189), a biologically active component of aqueous solutions of malononitrile

Abstract The formation of the 272-mμ chromophore which appears in varying concentrations in aqueous solutions of malononitrile was found to be base-catalyzed. This material was identified as 1,1,3-tricyano-2-amino-1-propene (U-9189), a dimer of malononitrile. The importance of this finding is discussed in relation to some of the known biochemical activities of U-9189 and to the questionable purity of malononitrile solutions used in other biochemical investigations.

Temperature Effects in Nuclear Magnetic Resonance Spectroscopy

The effect of temperature on the stability of the Varian V‐4300–2 NMR spectrometer has been investigated. The spectrometer was most sensitive to changes in room‐air temperature. A change of 0.3°C per minute caused a spectrometer drift of about 20 cps per minute. A change of 0.1°C per minute in temperature of magnet cooling water caused a spectrometer drift of 1 cps per minute. Enclosing the magnet served to minimize effects of air temperature changes but amplified the effects of water temperature changes. Satisfactory control was attained by running the refrigeration units continuously and regulating the temperatures by controlling the suction pressure on the evaporators. Under these conditions spectra were reproducible to within ½ cps.

The Analysis of ABX Spectra

Possible errors that may arise in interpreting ABX spectra are reviewed, and methods for detecting and avoiding these errors are discussed.