The Zeeman effect of chlorine nuclear quadrupole resonance in polycrystalline samples of 2,6-, 2,5 and 3,5-dichloro.phenol has been investigated at room temperature in order to study the effect of hydrogen bonding on the electric field gradient asymmetry parameter q. While the two n.q.r. lines in 3,5dichlorophenol gave an asymmetry parameter of x 10 %, those in 2,6-and 2,5-dichlorophenol gave different values of q for the two chlorines. The chlorine atom which is ortho to the OH group and involved in hydrogen bonding (k, corresponding to the low frequency line) gave an asymmetry parameter of0.21 in 2,6dichlorophenol and 0.17 in 2,5-dichlorophenol while the other chlorine ( i e . , corresponding to the high frequency line) gave a lower value of 0.12 in 2,6-dichlorophenol and 0.11 in 2,5-dichlorophenol. These values of q are discussed in terms of hydrogen bonding and bond parameters.

From consideration of 'H-lHresonances can be analysed to give two vicinal 'H-lH coupling constants, which are then used to provide approximate estimates of the rotamer fractional populations pI, pII and p,.', ' However, there are certain limitations in this method of analysis. For example, it is difficult to assign the C(@)H2 signals to their respective protons H-A and H-B and, consequently, one cannot assign the fractional population of rotamers I and I L 3 z 4 A further complication arises when the chemical shifts of the C(P)H, protons are similar; this leads to a deceptively simple spectrum from which only the sum of the vicinal 'H-IH coupling constants is obtainable and, under these conditions, only the fractional population of rotamer 111 can be calculated. A similar situation prevails for amino acids with only one P-proton, such as valine, which leads to only a single vicinal IH-IH spin coupling constant. The longrange 13C-lH vicinal coupling constants can be used in conjunction with 'H NMR studies to resolve the ambiguities pointed out above, provided that the values of the component vicinal coupling constants, J(CH)f and J(CH)g, are known accurately? The purpose of this investigation was to deduce the 13C component vicinal coupling constants by means of both 'H and 13C NMR studies.* Author to whom correspondence should be addressed THEORY -The conformation about the C(a)-C(P) bond in amino acids is best described in terms of the fractional populations, pI, pII and pIII, of the rotamers 1-111 shown in Fig. 1; these have previously been estimated from the vicinal 'H-IH spin coupling constants' with the following relationships:The measured vicinal coupling constants, J(AC) and J(BC), are average values of the gauche [J(HH)g] and trans [ J(HH)t] vicinal coupling constants in rotamers 1-111, weighted according to the fractional populations. The gauche and trans coupling constants are assumed to be the same in the three rotamers and the values used, J(HH)g= 2.6 and J(HH)t = 13.6 Hz, were obtained from model amino acid studies.''8 The carboxylate I3C three-bond couplings with the P-protons provide an additional set of equations involving the same rotamer molar fractions as illustrated in Fig. 1.Analogous to Eqns (1) and (2) for protons, the observed carboxylate 13C-'H vicinal coupling constants, J(A, CO) and J(B, CO), can be related to the component vicinal coupling constants J(CH) t and J(CH) g for

With the NMR lineshape-relaxation correlation technique the relaxation times and the relative magnitudes of the proton spin groups characterized by these respective relaxation times are obtained. In most tissues the spin-lattice relaxation in the rotating frame is nonexponential. The magnetization evolution can be represented as the sum of three exponential decays characterized by three T1rho relaxation times. The short T1rho component, corresponding to the rigid network protons, gives the most interesting information on the tissue. Results at 38 MHz are given for muscle, spleen, lung, and tumor EMT6 fibrosarcoma grown in the dorsal subcutaneous tissue of BALB/c mice. The absence of the magnetization component with short T1rho and short T2 in spleen tissue of tumorous mice demonstrates that the spleen is swollen to at least 5 times its original size so that the relative magnitude of the magnetization corresponding to collagen network is proportionally reduced. The NMR correlation technique is thus shown to be appropriate for such quantitative analysis.

The frequency dependence of the spin-lattice relaxation time T1 was measured at three temperatures near one of the Zeeman-tunneling level matching resonances for pentamethylbenzene. These measurements are correlated with 71 temperature dependence data from the literature. It is shown that the frequency dependence of the Zeeman-torsion coupling time cannot be explained in terms of the semiclassical perturbation theory using time correlation functions. A three bath polarization transfer model is also employed and the applicability of both models discussed. Zeeman-torsion coupling is further investigated using a saturation sequence and the results are compared with the predictions of the three bath polarization transfer model.

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