Dean C. Douglass

Self‐Diffusion in Liquid Water to −31°C

The self‐diffusion coefficient of water is reported to −31°C, where the activation energy reaches 11 kcal/mole compared with 4.5 kcal/mole at 25°C. The similarity of the temperature dependence of the fraction of broken hydrogen bonds, as inferred from Raman and infrared data, and the diffusion coefficient over the entire liquid range forms the basis of empirical support of the dominant role of hydrogen bonding in the fundamental diffusion mechanism.

Nuclear Magnetic Relaxation of n‐Alkanes in the Rotating Frame

The rotating‐frame nuclear magnetic relaxation time T1ρ has been measured for 10 normal alkanes ranging from C4H10 to C94H190. Data were obtained within the range −200° to +70°C for C94H190, C40H82, and C6H14. The high‐temperature region is characterized by a process of high activation energy ascribed to chain rotation while the low‐temperature region exhibits a T1ρ minimum arising from coupling of the entire spin system to the methyl‐group rotation via spin diffusion. This information and the analogous T1 data yield an activation energy of 2.6 kcal/mole for the methyl‐group rotation. The remaining compounds were examined in the vicinity of the T1ρ minimum at −190°C and relaxation times characterizing the intrinsic methyl relaxation and spin‐diffusion process have been extracted from the data for three rf field strengths. Theoretical estimates of the spin‐diffusion coefficients at low fields and methyl‐proton relaxation times are in satisfactory agreement with the observed quantities.

Diffusion in Liquids

Self‐diffusion coefficients have been measured for water, nitromethane, acetone, benzene, cyclohexane, isopentane, and neopentane. Temperature and pressure dependences have been determined for nitromethane, acetone, cyclohexane, and isopentane. The temperature dependence has been determined for neopentane and the pressure dependence has been determined for water and benzene. The results are discussed in terms of a semiempirical theory for transport in liquids and it is shown that semiquantitative predictions of self‐diffusion, viscosity, and thermal conductivity coefficients can be made.

Molecular Motions in Several Solids Studied by Nuclear Magnetic Relaxation in the Rotating Frame

Rotating frame nuclear magnetic relaxation times have been measured as a function of temperature from 117 to 290°K for perfluorocyclohexane, cyclohexane, 2,2‐dichloropropane, neopentane, and tetramethylammonium iodide. The data are interpreted in terms of molecular rotation and diffusion in the solid state.

Molecular Motion in ortho‐Terphenyl

Nuclear magnetic relaxation measurements have been made for ortho‐terphenyl in the liquid, crystalline, and glassy form. Self‐diffusion coefficients have been measured in the liquid. Molecular correlation frequencies derived from these measurements are shown to correlate well with published viscosity data. The results were found to be described satisfactorily by an equation of the form νc = A″ exp[−B′ / (T−Tg)], but not by an equation of the form νc = A exp(− C / TSc), where Sc is the configurational entropy. Comments are made on the derivation of these functions and the nature of the molecular motions.

Nuclear Magnetic Resonance in Solid Adamantane

Proton magnetic resonance studies of solid adamantane reveal the existence of a rotational transition at about —130°C. The activation energy associated with the rotational transition is found to be about 5 kcal/mole. Theoretical and experimental second moments agree if it is assumed that the molecules are rigidly fixed below the transition and rotate freely above the transition.Proton magnetic resonance studies of solid adamantane reveal the existence of a rotational transition at about —130°C. The activation energy associated with the rotational transition is found to be about 5 kcal/mole. Theoretical and experimental second moments agree if it is assumed that the molecules are rigidly fixed below the transition and rotate freely above the transition.

Diffusion in Ethylene Polymers. IV

Self‐diffusion coefficients have been measured for two low molecular weight fractions (M = 4100 and 5800) of a linear polyethylene. The activation energy for the M = 4100 fraction is 5.3 kcal/mole which is near the value 5.6 kcal/mole found for n — C32H66. At 150°C, for this fraction, D = 1.6×10—7 cm2/sec and as 10—7 is near the lower limit of detectability the activation energy is probably not accurately determined. The diffusion coefficient for the M = 5800 fraction is 1.1×10—7 cm2/sec at 150°C. These results, combined with previous results, show that D = κn—5/3, where D is the coefficient of self‐diffuison for the normal paraffin CnH2n+2. κ is a constant at a given temperature, 4.5×10—3 cm2/sec at 200°C and 2.5×10—3 cm2/sec at 150°C.

NMR shift and diffusion study of dioxane-H2O and pyridine-H2O mixtures

Abstract A nuclear magnetic resonance investigation has been carried out on dioxane-water and pyridine-water mixtures over the entire concentration range. In both systems, proton resonance shifts of each component showed a marked concentration dependence, indicating the presence of strong interactions, probably hydrogen bonding. In addition, an estimation was made of the magnitude of the effect of “ring-currents” operating in the aromatic pyridine. Self-diffusion coefficients of the nonaqueous component of dioxane-D 2 O and pyridine-D 2 O mixtures were measured by the nuclear magnetic resonance spin-echo technique. The data again indicated the presence of associative processes in both systems.

Self‐Diffusion in Liquids: Paraffin Hydrocarbons

The pressure dependence of the self‐diffusion coefficients of several normal paraffin hydrocarbons and the isomers of hexane have been determined. In addition, the temperature dependence of self‐diffusion coefficients has been measured for the isomers of hexane. Energies and volumes of activation have been calculated. With the exception of 2, 2‐dimethyl butane, these parameters do not change significantly with branching in the isomers of hexane. The volumes of activation are about 10–20% of the molar volumes in all cases. Diffusion coefficients computed from a semiempirical modification of an equation derived by Longuet‐Higgins and Pople are compared with the experimental results.

Polymer NMR Spectroscopy. X. The Use of H1–H1 Spin Decoupling in the Elucidation of Polymer Structure

High‐resolution NMR spectroscopy of vinyl polymers in solution is an effective means of determination of the stereochemical configuration of their chains. In polymers having only a single α substituent, however, spin coupling of α and β protons complicates the interpretation of the spectrum considerably and also makes it difficult to observe those stereoisomeric sequences which are present as minor components. Decoupling of the α‐ and β‐proton spins has been found to be helpful in the interpretation of the spectra of polyvinyl chloride, polyvinyl fluoride, and polyvinyl methyl ether. It is not helpful for polyvinyl acetate in carbon tetrachloride, since here the chemical shift of the α and β protons is not sensitive to stereochemical configuration.