The viscosity and surface tension of dispersions of sucrose, lactose, skim milk powder, and butterfat

Thesis (M.S.

The analysis and interpretation of high resolution nuclear magnetic resonance spectra

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1958.Vita.Includes bibliographical references (leaves 103-104).by Richard Warren Fessenden.Ph.D

ESR spectra of PF_2 and SF_3 radicals

[No abstract

ESR studies of internal rotation in radicals

The β hyperfine splittings in the ESR spectra of a number of alkyl radicals were previously shown to be temperature dependent. The results of detailed measurements over a range of temperatures are presented here for propyl, isobutyl, 3-butenyl and CHD2CD2• radicals. The dependence, for radicals of this type, of the coupling constant upon cos2 of the azimuthal angle, θ, between the particular β proton and the axis of the p orbital containing the unpaired electron suggests that the departure of the splittings from that found for ethyl radical arises from an anisotropic averaging over the rotation about the bond between the α and β carbons and that the temperature dependence reflects the expected changes in this averaging with temperature. A treatment is applied which averages cos2 θ first over the rotational eigenfunctions for the case of a two-fold barrier to internal rotation and then over a Boltzmann distribution among the various rotational levels. The observed splittings are obtained if barriers of the order of 300 cal/mole are taken for the first three radicals and if a 90 cal/mole barrier is used for CHD2CD2•. A discussion is presented which attempts to show the relationship of these barriers to those found in other molecules. The similarity is noted of the isotope effect in CHD2CD2• and that in 7-deutero-cycloheptatriene which causes a slight preference for one of the two ring configurations

A study of the photoionization of anion radicals in aqueous solution

The photolysis of a number of radical anions of substituted aromatic carboxylic acids has been investigated by two-pulse experiments using pulse radiolysis and laser photolysis. The aim of the study is to determine the photophysical and photochemical processes that follow optical excitation of these radicals. Photoionization with varying quantum efficiencies from 0.4 for benzoate dianion radical to <0.01 for anion radicals of formyl-, acetyl-, and benzoylbenzoic acids is found to be the only process in all but a few special cases. In no case was luminescence of the radical observed. The quantum yields seem to be strongly affected by structural factors even when the energetics are favorable. Because the radicals selected for study absorb in the visible region, it has thus been possible to examine the process of charge separation with photons of a much lower energy than is necessary for most normal molecules. It is hoped these results may provide insights that will be of value in the design of systems to provide useful conversion of solar energy

Sensitized and heavy atom induced production of acenaphthylene triplet: a laser flash photolysis study

The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max}=315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry

Excited-state dipole moment of 7-aminocoumarins as determined from time-resolved microwave dielectric absorption measurements

The excited-state dipole moments of several structurally related 7-aminocoumarin derivatives, used as laser dyes and in nonlinear applications, have been measured directly by following time-resolved changes in photoinduced microwave dielectric absorption. The dipole moments of the systems in the fluorescent state lie between 8.1 and 11.9 D, and the changes in the dipole moment on electronic excitation range between 1.7 and 6.1 D. Further, the excited-state dipole moment of any given system is found to be almost the same in benzene and in 1,4-dioxane. The results unambiguously suggest that these aminocoumarins fluoresce from the locally excited state and not from a zwitterionic or twisted intramolecular charge-transfer state, as often indicated in the literature