David N. Lincoln

MERCURY CONTENT OF COMMON FOODS DETERMINED BY NEUTRON ACTIVATION ANALYSIS.

The mercury contents in samples of flour, sugar, nonfat dry milk, potatoes, hamburger, chicken breast, shrimp, liver, eggs, and whole milk were determined by neutron activation analysis. The mercury was separated by anion exchange chromatography and precipitated as the sulfide. The mercury concentrations for all these foods were below 50 parts per billion.

The complete 13C, 19F, and 1H spectral analysis of the fluorobenzenes C6HnF6−n. II. 1,2-Difluorobenzene. INDO MO calculations of JHH in these fluorobenzenes and related molecules

Abstract The complete high-precision spectral analyses of the per-12C- and the naturally abundant 13C-isotopomers of 1,2-difluorobenzene are presented. The coupling constants and isotope effects upon the chemical shifts are discussed. INDO-SCF MO calculations of JHH in the fluorobenzenes C6HnF6-n and related systems were performed and the results compared with experimental data.

The complete 13C, 19F and 1H spectral analysis of the fluorobenzenes C6HnF6∼-n.I.1,3,5-trifluorobenzene

The complete high-precision spectral analyses of the per-12C- and the two naturally abundant 13C-isotopomers of 1,3,5-trifluorobenzene are presented. All the secondary isotope effects upon 19F and 1H chemical shifts are evaluated. There is no detectable isotope effect for 13C substituion upon 4JHH and 4JFF. The signs of the coupling constants were determined from the analyses and heteronuclear tickling experiments and are discussed. Comparisons are made with the proton-carbon coupling constants of the meta-halobenzenes.

Additivity of substituent effects upon proton–fluorine coupling constants in polysubstituted fluorobenzenes

Substituent effects upon JFH values in polysubstituted fluorobenzenes are demonstrated to be additive for the substituents F, Cl, Br, I, NO2, NMe2, and OMe. An evaluation of the substituent constants by a regression analysis allows the accurate calculation of 230 JFH values in 70 compounds. The consequences of this analysis for the resolution of the ambiguities in the assignment of 3JFH and 4JFH values, and of the sign of 5JFH in many reported JFH values are discussed. The variation of the substituent constants with substituent electronegativity, EX, are considered and an assessment of the literature reports of the correlation of JFH with EX is made.

Fourier transform 13C nuclear magnetic resonance studies of steroids. Part I. Some substituted 17β-(2,5-dihydro-5-oxo-3-furyl) steroids

The natural abundance 13C n.m.r. spectra of several substituted (2,5-dihydro-5-oxo-3-furyl) steroids, having hydroxy-groups at various positions in the steroid nucleus, have been measured. The effects of changes in the structure of the steroid nucleus upon substituent chemical shifts are evaluated and discussed.