John A. Weil

Conformation and Internal Rotation of Nitroaromatic Amines in Solution as Detected by Proton Magnetic Resonance

The 60‐Mc/sec proton magnetic resonance spectra of N‐methyl‐2,4,6‐trinitroaniline (I) and of N‐methyl‐2,6‐dinitroaniline (II), as well as of the analogous N‐diphenylamino compounds, show that the 3‐ and 5‐phenyl protons are inequivalent at low temperatures in solution, but act as equivalent at sufficiently high temperatures. The N‐unsubstituted anilines and N,N‐dimethyl anilines corresponding to I and II show no such inequivalence. The coalescence with temperature of the AB quartet of the picryl protons in the picrylaniline (I) and diphenylpicrylhydrazine in dichloromethane solution could be described quantitatively by the line‐shape equations for two coupled protons exchanging with each other. The analysis yielded the lifetimes of the ground state configurations of these molecules, with Arrhenius activation energies of 14.5±0.3 and 12.5 ± 0.2 kcal/mole and frequency factors of 1.4×1015 and 6×1010 sec—1, respectively, for the intramolecular exchange process. A model for these observations, including Hucke...

Germanium‐Hydrogen‐Lithium Center in α‐Quartz

A new center, denoted by GeHLi2, has been observed by EPR to be present in alpha‐quartz containing germanium, after room temperature x irradiation. The spin Hamiltonian at 8909 MHz and 300°K has been measured, yielding the Zeeman splitting tensor ḡ and the hyperfine coupling tensors Ā (73Ge), Ā (1H), Ā (7Li1), and Ā (7Li2). From the principal values and axis directions, a model for the center of the form Ge3+H−(Li+)2 has been derived. This postulates germanium to be present substitutionally at a silicon site, with the hydride and two lithium ions occurring interstitially nearby. The unpaired electron is thought to be in a Ge orbital a(4s) + b(4p), with |a|2∼ 0.18 and |b|2 ∼ 0.35, with considerable spin density also at the hydrogen. The center may be formed from a diamagnetic precursor Ge2+(Li+)2 by reaction with a hydrogen atom.

The analysis of large hyperfine splitting in paramagnetic resonance spectroscopy

A simple method for analysis of large hyperfine splittings in EPR spectra arising from S = 12 systems is discussed. The technique sets out from the Breit-Rabi formulation and brings in anisotropies as perturbations. As an example, the calculation of the 73Ge hyperfine tensors of two germanium centers (AGeLi and CGeLi) in x-irradiated α-quartz is discussed.

Hyperfine Structure in the Solution ESR Spectrum of Di‐tert‐butyl Nitroxide

Isotropic splitting constants for 14N, 15N, 13C, and 17O nuclei present in natural abundance in di‐t‐butyl nitroxide have been measured by electron spin resonance, using benzene solutions at room temperature. The proton hyperfine structure was not resolved, but was estimated from best‐fitting computer‐simulated spectra. Comparison of computer‐simulated single‐ and double‐substitution 13C satellites with the experimental satellites indicates that only six of the eight positions contribute to these satellites.

Conformation and Internal Rotation of Nitroaromatic Amines in Solution as Detected by Proton Magnetic Resonance. II. Polynitro Acetanilides

The proton NMR spectra of several N‐acetyl‐N‐methyl polynitroanilines reveal the presence of two conformers. The conformer ratio has been studied for the picrylaniline in various solvents, and the rate of conformer interchange for this substance was measured in 1,4‐dioxane. Chemical‐shift studies of these and various related molecules have given additional information about the configuration of these molecules. It is concluded that the acetamide group is normal to the plane of the aromatic ring for the N‐acetyl‐N‐methyl‐2,4,6‐trinitro and 2,6‐dinitro anilines.