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Here Aveq and Av&x are the contact shifts for a given proton in the "frozen" equatorial and axial environments and X\ and Xs are the mole fractions of the chelate rings in the X and conformations.28 The methylene protons in the Ni(II) complex of AT-methylethylenediamine are observed at -112 and -127 ppm.7 Our results suggest that the "frozen" contact shifts for the primary amine would be the same as for the ethylenediamine complex, namely, Aveq = -162 and = -10 ppm, and that the primary amine proton would be the one observed at Ajobad = -112 ppm. Making these substitutions and remembering = 1 -Xs, we can calculate Xs = 0.66 from eq 4. This means that twice as many methyl groups are in equatorial as axial (28) When a ring changes from the to the X conformation, a proton is moved from an equatorial to an axial position.Cole, Curthoys, Magnusson, and Phillips positions. Ho and Reilley reported 4 times as many equatorial as axial methyl groups for IV.iV'-dimethylethylenediamine, which has twice as many methyl groups and hence greater preference for the conformation. Using this value of Xs and assuming that the shift of the axial proton for the secondary amine is -6 ppm, as it is in N, '-dimethylethylenediamine, we can write eq 4 for the signal at -127 ppm with only Aveq as an unknown. We then find Aveq for the secondary amine is -189 ppm which is in excellent agreement with the -188 ppm reported by Ho and Reilley7 for N,Nfdimethylethylenediamine. Thus the assignment of the peak observed at -127 ppm to proton b is consistent with the reported shifts of ethylenediamine and N,N'dimethylethylenediamine and our calculations.

A brief review of how to interpret the data of heats of adsorption by gas-solid chromatography is needed to avoid some of the common confusion experienced by beginning investigators in this field.

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