It is shown that the frequency shifts of the NH stretching mode of pyrrole in a variety of different solvents can be plotted directly against the corresponding shifts of many X-H stretching vibrations in the same solvents. The significance of the results obtained is discussed in relation to complex formation and hydrogen bonding.

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The carbonyl frequencies of a wide range of compounds have been studicd in many solvents. The frequency shifts all follow a common pattern and seem to be produced mainly by local association effects, and not by dielectric constant factors. The relative sensitivities of carbonyl groups to solvent effects have been measured in this way, and the significance of the results is discussed. These findings may have other useful applications in diagnostic work and in Fermi resonance studies.

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