Keith F. Purcell

Spectroscopic studies of hydrogen bonding: Hexafluoroisopropanol☆

Abstract The shifts of the OH stretching frequency and OH proton shielding constant of 1,1,1,3,3,3-hexafluoro-2-propanol upon hydrogen bond formation are reported. Oxygen, nitrogen, and sulfur donors of various types were used as Lewis electron pair donors. A correlation between the frequency and shielding constant changes is found and compared with those for phenol and 2,2,2-trifluoro-ethanol. The use of this data to index the acidities of these alcohols and the magnitides of the acid-base interactions is discussed. The influence of the substituent on the nature of chemical shift, frequency correlations is examined. The nonzero intercepts of the chemical shift, frequency shift correlations are discussed in terms of the generalized Lippincott-Schroeder one dimensional model for hydrogen bonded adducts, from which the importance of donor to hydrogen charge transfer is inferred. The data also appear to require a correction of about 0.5 ppm to the proton chemical shift when the donor atom is sulfur. The diethylsulfide, hexafluoro-2-propanol OH frequency shift appears to be anomolously low by about 75 cm−1 and results in a spectroscopic reversal of base strength.

Localized virtual and occupied molecular orbitals

This report describes the generation of localized from canonical molecular orbitals such that the method (1) be consistently applicable to occupied bond, lone pair and unoccupied orbitals and (2) permit symmetry related orbitals in molecules of two-fold or higher symmetry. Minimization of populations completely external to each local pair region effectively meets these criteria. Finally, conventional strategy for finding the global extremization point is costly in time and memory to implement; a much more efficient numerical search procedure for the global extremum is described. Results for ethylene, butadiene and benzene are presented to clarify the difficulties and their resolution.

State‐of‐the‐art time‐resolved emission Mössbauer spectrometer

We report on the design, construction, and operation of a time‐resolved emission Mossbauer spectrometer which has as its central component a microcomputer for data recording and manipulation. The philosophy of data acquisition affords previously unrealized flexibility in data handling and spectral analysis in both the time and frequency domains.

Etudes théoriques sur le mécanisme de formation d'un epoxyde à partir d'un métallocycle. L'étape de cycloréversion

Abstract Extended Huckel calculations of various intermediates for the reaction of olefins with MoO(O2)2L2 confirm the viability of olefin coordination and metallocycle formation trans to the oxo ligand. Frontier orbital changes and couplings revelant to concerted elimination of epoxide from the metallocyclic unit MoOOCH 2 C H2 by a cycloreversion step reveal the importance, even in such polar systems, of the antarafacial alignment of the frontier orbitals.

Bonding and frequency shifts in XN2 and XCO compounds

Abstract The origin of the general experimental observation that ΔF N 2 >ΔF co for N 2 vs. XN 2 and CO vs. XCO is discussed. The relative donor-acceptor properties of N 2 and CO are examined in general terms applicable to a wide range of π donor substituents, X. Specific examples, for illustrative purposes, are X = N − and O. These simple substituted N 2 and CO compounds have been treated by rigorous SCF procedures and those results form a quantitative basis for the discussion.

The influence of hyperconjugation on properties of borane adducts

Primarily exploratory calculations, using CN/INDO methods, into the influence of hyperconjugation on molecular properties of borane adducts are presented. Discussion centers around the molecule BH3CO. While the theoretical methods are relatively crude, useful generalizations emerge which suggest the need for treatment by less approximate methods and/or suggest what experiments are likely to yield information about the concept of hyperconjugation. The properties discussed are structure, energy, nuclear spin-spin coupling, nuclear quadrupole coupling, photo-electron spectra, and infrared band intensities.

Molecular Orbital Treatment of Activation Induced by Electron Attachment. Application to Electron Transfer Catalysis

In a first paper dealing with the generalization of electron transfer catalysis, we suggested that the common feature shared by all mechanisms, is the existence, at a cr itical step, of an activation induced by electron transfer (1). By “activation”, we mean a marked enhancement of reactivity for a given transformation; by “induced by electron transfer”, we mean that such an activation may result from electron attachment to the substrate as well as from electron removal from the substrate. In that first report, illustrative examples were selected from inorganic and organic chemistry to show that rate enhancements associated with such an activation could reach values as high an 1015 (Table 4 in ref.1). Two main types of activation were identified: associative activation and dissociative activation.

A spin anomaly and second order substituent effect for localized spin orbitals

The spin polarization pattern of geminal CH bond pairs was determined using the UHF‐INDO finite perturbation technique. (AIP)