No abstract

The electron paramagnetic resonance of a number of alternant methylene compounds has been observed, and zero-field splitting parameters have been obtained. The results are D=0.6276±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–H,D=0.6263±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–CH3,D=0.5413±0.0004 cm−1 and E=0.0035±0.0003 cm−1 for H–↑C↑–C≡C–C6H5,D=0.6087±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–CH3,D=0.6055±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–C(CH3)3,D=0.5530±0.0002 cm−1 and E=0.0000±0.0006 cm−1 for H–↑C↑–C≡C–C≡C–C6H5,and D=0.8629±0.0003 cm−1 and E=0.0000±0.0010 cm−1 for H–↑C↑–C≡N.The interpretation of the data is based upon the observed spin-density distribution in the alternant free radicals having structures similar to the above triplet molecules. Thus, propargylene, H–↑C↑–C≡C–H, is discussed in terms of a superposition of two π-electron systems having the same spin-density distribution as in the allyl radical. Both positive and negative triplet spin densities are required to account for the observed magnitude of D. The lower values of D obtained for the phenyl-substituted alternant methylenes reflect the delocalization of one of the two triplet electrons into a π orbital of the phenyl group. This effect is more important in the case of phenylpropargylene where a nonzero value of E was obtained. The linear geometry of the alternant methylene chain is responsible for the cases where zero values of E were obtained. The trends in D and trends in linewidths are given qualitative explanations. The discussion assumes that all of the molecules studied have a spectroscopic splitting factor equal to the free-electron value.

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The nuclear magnetic I elaxation times of protons in aqueous solutions of paramagnetic ions have been measured as a function of temperature. For Mn++ ions, the proton TI and T2 were measured at 10 20 and 28 Mc/sec, and for Co++, Cu++, and Gd+++ ions, 20 Mc/sec. The temperature effects observed ca~ b~ explained by incorporating the proper temperature dependences of the several correlation times into the general Bloembergen· Solomon relaxation expressions.In the ~ase of Mn++ solutions, which have a TJ/T2 ratio of about 5.5 at room temperature and 20 Mc/ sec, chemtcal as well as electron exchange and dipolar interactions are found to be important. Analysis of the data by mean? of the e~uations developed pro~ides information concerning the chemical exchange of solvent protons with those m the hydrated Mn++ IOn. An activation energy of 8.4 kcal/mole and other parameters for this process are evaluated.The temperature dependence of TI and Tz in the Co++, Cu++, and Gd+++ solutions can be explained by the temperature dependence of the dipolar interaction alone. Varying the anion in Cu++ solutions had little effect on 1' .1 or its temperature dependence; also, TI for Cu++ solutions was found to vary inversely with concentratIOn over the whole temperature range studied.