SPIN ECHOES IN ALCOHOLS AND DERIVATIVES

Abstract

The spin echo technique has been employed to measure the relative chemical shifts and the indirect spin–electron–spin coupling constants between protons at different structural sites in ethyl, propyl, isopropyl, butyl, isobutyl, and amyl alcohols and certain of their derivatives at a Larmor frequency of 29.0 Mc./s. The separation between the two r-f. pulses applied to the sample increases regularly in accurately known steps which are controlled electronically. Thus the frequencies modulating the echo envelope have been readily measured with a precision as high as 4% in favorable cases. Relative chemical shifts found by slow passage experiments have been checked with higher accuracy, particularly for the primary alcohols. Encouraged by the implications of these earlier data, we have here analyzed the longer hydrocarbon chains on the basis of the theoretical computations of Hahn and Maxwell for only two groups of non-equivalent protons. This more precise investigation confirms the assumptions made as to where the major shifts and couplings do and do not exist in the molecular structures. In the halide molecules, it is found that the observed relative chemical shifts are linearly proportional to the paramagnetic fields arising from the valence orbits of the halogens polarized by the external field. Evidence for the particular J-coupling to the hydroxyl group in the alcohols suggests that this bond is effectively stronger in the heavier molecules which are only slightly soluble in water.