The Huckel theory, with an extended basis set consisting of 2s and 2p carbon and 1s hydrogen orbitals, with inclusion of overlap and all interactions, yields a good qualitative solution of most hydrocarbon conformational problems. Calculations have been performed within the same parametrization for nearly all simple saturated and unsaturated compounds, testing a variety of geometries for each. Barriers to internal rotation, ring conformations, and geometrical isomerism are among the topics treated. Consistent σ and π charge distributions and overlap populations are obtained for aromatics and their relative roles discussed. For alkanes and alkenes charge distributions are also presented. Failures include overemphasis on steric factors, which leads to some incorrect isomerization energies; also the failure to predict strain energies. It is stressed that the geometry of a molecule appears to be its most predictable quality.

An Extended Hückel Theory. I. Hydrocarbons

A statistical mechanical treatment of high polymer solutions has been carried out on the basis of an idealized model, originally proposed by Meyer, which is analogous to the one ordinarily assumed in the derivation of the ``ideal'' solution laws for molecules of equal size. There is obtained for the entropy of mixing of n solvent and N linear polymer molecules (originally disoriented), ΔS=−k[(n/β) ln v1+N ln v2] where v1 and v2 are volume fractions and β is the number of solvent molecules replaceable by a freely orienting segment of the polymer chain. This expression is similar in form to the classical expression for equal‐sized molecules, mole fractions having been replaced by volume fractions. When the disparity between the sizes of the two components is great, this expression gives entropies differing widely from the classical values, which accounts for the large deviations of high polymer solutions from ``ideal'' behavior. The entropy of disorientation of a perfectly arranged linear polymer is found t...

Thermodynamics of High Polymer Solutions

The necessary coordination of the motions of different parts of a polymer molecule is made the basis of a theory of the linear viscoelastic properties of dilute solutions of coiling polymers. This is accomplished by use of the concept of the submolecule, a portion of polymer chain long enough for the separation of its ends to approximate a Gaussian probability distribution. The configuration of a submolecule is specified in terms of the vector which corresponds to its end‐to‐end separation. The configuration of a molecule which contains N submolecules is described by the corresponding set of N vectors. The action of a velocity gradient disturbs the distribution of configurations of the polymer molecules away from its equilibrium form, storing free energy in the system. The coordinated thermal motions of the segments cause the configurations to drift toward their equilibrium distribution. The coordination is taken into account by the mathematical requirement that motions of the atom which joins two submolecules change the configurations of both submolecules. By means of an orthogonal transformation of coordinates, the coordination of all the motions of the parts of a molecule is resolved into a series of modes. Each mode has a characteristic relaxation time. The theory produces equations by means of which the relaxation times, the components of the complex viscosity, and the components of the complex rigidity can be calculated from the steady flowviscosities of the solution and the solvent, the molecular weight and concentration of the polymer, and the absolute temperature. Limitations of the theory may arise from the exclusion from consideration of (1) very rapid relaxation processes involving segments shorter than the submolecule and (2) the obstruction of the motion of a segment by other segments with which it happens to be in contact. Another possible cause of disagreement between the theory and experimental data is the polydispersity of any actual polymer; this factor is important because the calculated relaxation times increase rapidly with increasing molecular weight.

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A Theory of the Linear Viscoelastic Properties of Dilute Solutions of Coiling Polymers

https://febs.onlinelibrary.wiley.com/doi/epdf/10.1016/0014-5793%2873%2980770-7

Biological interactions between polysaccharides and divalent cations: The egg‐box model

Fluidity Parameters of Lipid Regions Determined by Fluorescence Polarization

The Viscous Flow of Large Molecules

Solute‐solute interactions in aqueous solutions of nonelectrolytes are interpreted using both lattice and distribution function theories of the dissolved state. Experimental activity data of high precision can be obtained from the literature for aqueous solutions of many nonelectrolytes. If the logarithm of the solvent activity coefficient (γ1) is expressed as a power series in the mole fraction of the solute (x2), lnγ1 = Bx22 + Cx23 + ···, then the coefficients B and C can be determined analytically from the experimental measurements. Values of B were obtained for 52 aqueous mixtures; values of C were obtained for 39 of these mixtures. The solutes considered include aliphatic alcohols, amines, amides, ketones, fatty acids, amino acids, and sugars. In some cases, experimental data were available from which the temperature dependence of the quantities B and C could also be determined. The effect of solute size on the coefficients B and C was investigated using the lattice theories of Flory, Huggins, and Gu...

Solute‐Solute Interactions in Aqueous Solutions

It is shown that the numerical value of the optical activity of an optically active compound is markedly reduced if the groups surrounding the asymmetric atoms in the compound possess a threefold axial symmetry about the bonds connecting them with the asymmetric atoms. This threefold symmetry may be either inherent in the groups themselves, or it may be acquired by them through the free rotation of the groups about these bonds or by their orienting themselves to equal extents in each of the three possible equilibrium positions about each bond. The order of magnitude of the numerical value of the optical activity is thus a measure of the freedom of orientation about single bonds of the groups in an asymmetric molecule. That this effect is actually a dominant factor in determining the order of magnitude of the optical activity is proved by the contrast in the optical activities of cyclic and open chain compounds. It is shown to have an important effect on the temperature coefficient of optical activity and ...

The Effect of the Rotation of Groups about Bonds on Optical Rotatory Power

The activation energies of the reactions H+CH4=CH3+H2 (1) and D+CH4=CH3D+H (2) have been calculated by using the semi‐empirical method in combination with the treatment of directed valence used by Van Vleck and Voge. The activation energies for reactions (1) and (2) were found to be 9.5 kcal. and 37 kcal. This result agrees with the prediction of 40 kcal. of Rice and Teller for reaction (2). In addition it is found that the energy surface corresponding to the reaction H+CH4 contains a basin 8 kcal. deep corresponding to a stable CH3–H–H molecule. The rapid recombination of H atoms in the presence of methane, observed by Farkas and Melville is interpreted in terms of this CH3–H–H intermediate. The experimental data on the reactions of hydrogen and deuterium atoms with hydrocarbons have been reinterpreted in terms of atom‐cracking reactions of the type D+C2H5→C2H5D→CH3D+CH3.

Walter Kauzmann

Papers

The Viscous Flow of Large Molecules

Solute‐Solute Interactions in Aqueous Solutions

The Effect of the Rotation of Groups about Bonds on Optical Rotatory Power

Reactions Involving Hydrogen and the Hydrocarbons

The Kinetics of Hydrolysis of Ribonucleic Acid