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Solutions were run in standard 0.1-mm cells equipped with sodium chloride or potassium bromide windows. The solution concentrations were as low as practicable, and in all cases were less than 0.5 M. Results and Discussion(4) . E. Hallara and T. C.

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The infrared and Raman spectra of p-fluoro-, p-chloro-, p-bromo-, and p-iodo-propionitrile have been obtained over the complete fundamental vibrational frequency range. Solid-state i.r. spectra have also been measured. The results show that each of these compounds exists as an equilibrium mixture of gauche and trans isomers. In all cases the gauche isomer is the more stable form in the liquid phase. Enthalpy differences have been determined for the chloro-, bromo-, and iodo-derivatives. A vibrational frequency assignment has been made for each of the isomers and this has been tested by application of the sum rules.1 ,~-DISUBSTITUTED ethanes usually exist as mixtures of two energetically favoured isomers, the trans and gauche forms. A recent i.r. spectroscopic investigation has shown that this is the case for liquid P-chloro-, P-broino-, and 8-iodo-propionitrile. The present work has extended the i.r. frequency range studied to include the entire range where fundamental vibrations might be observed. Raman data have also been obtained for the first time. p-Fluoropropionitrile, for which no previous spec troscopic result was available, has also been studied.The present investigation, which partially overlaps E. Wyn-Jones and W. J. Orville-Thomas, J . Chem. SOC. ( A ) ,

In investigating liquid-phase proton NMR spectra of 2,2-dimethyl-1-(2,4,6-trinitrophenyl)hydrazine in various solvents, we have found an interesting correlation, at sufficiently low temperatures T, between the chemical-shift difference (splitting) of the picryl proton peaks, measured as f(T), and the Kamlet–Taft hydrogen-bonding basicity parameter β. The observed solvolytic effect offers a convenient way of determining and checking the value of the empirical parameter β. The phenomenon discloses that the molecular geometric configuration is affected vividly by hydrogen bonding with the surrounding solvent molecules. It follows that the internal conformation interchange taking place (in a higher T range) is not in fact solely a unimolecular property.Key words: picryl proton NMR, chemical shift, solvent effects, hydrogen bonding, Kamlet–Taft β.