Stanford L. Smith

Solvent Effects on H–F Couplings: Dipole Orientation Requirements for Solvent Dependence of Coupling Constants

Solvent‐dependent variations of 2JHF, cis 3JHF, and trans 3JHF have been observed in trifluoroethylene and vinyl fluoride. These data, in conjunction with previous observations, indicate that orientation of the solute dipole strongly affects the solvent dependence of geminal coupling constants. The electric field of the solvent appears to be the primary causative factor, but strong molecular associations (e.g., H bonding) may either enhance or decrease the observed effect. The limited results available suggest that the absolute sign of 2JHF may be obtained by observing the change of 2JHF as a function of solvent.

Solvent Effects on Geminal H–H Couplings: A New Method for Determining Signs of Coupling Constants

Solvent‐dependent variations of geminal coupling constants have been observed in styrene oxide, styrene sulfide, 1,4‐diphenylazetidinone, and 4‐methyl−1,3‐dioxolane. These data, in conjunction with previously reported observations, suggest that Jgem always becomes more negative in the absolute sense in solvents having higher dielectric constants. The reaction field of the solvent seems to be the primary causative factor. The magnitude of the effect is shown to depend on the orientation of the dipole moment of the solute molecule with respect to the H–C–H plane. Qualitative theoretical considerations support the existence of a direct correlation between the observed changes and the absolute sign of Jgem and suggest that the magnitude of the change in Jgem also depends on the relative magnitude of the hyperconjugative contribution to Jgem.

Studies on the Influence of pH and Pancreatin on 13C-Formaldehyde-Induced Gelatin Cross-Links Using Nuclear Magnetic Resonance

Carbon-13 nuclear magnetic resonance (13C-NMR) and 13C-enriched formaldehyde (13CH2O) were utilized to observe cross-linking in gelatin. Thus, when a 6% solution of gelatin in water was treated with 2000 ppm 13CH2O at 20 degrees C, the 15 hr 13C-NMR spectrum of the crosslinked gel showed peaks representing carbinolamines (methylols) of arginine and lysine, as well as a peak ascribed to a methylene cross-link between arginine and lysine. Similar results were obtained when these cross-linking reactions were conducted using only 100 ppm 13CH2O. When pancreatin (1% w/v) was added to the solution of 6% gelatin cross-linked with 2000 ppm 13CH2O, the gel began to revert to a clear fluid solution. After incubation for 24 hr at 37 degrees C, the 13C-NMR spectrum of this solution confirmed the presence of the methylols of lysine and arginine, and the lysine-arginine cross-link. When 13CH2O (2000 ppm) was added to a 6% solution of gelatin at pH 13.0, the arginine methylol and the lysine-arginine crosslinks were produced. The 13CH2O-induced crosslinking of gelatin at pH 2.0, however, yielded the lysine methylol as the sole product.

Solvent dependent coupling constants in fluoromethanes

Abstract Difluoromethane and trifluoromethane have been examined in solvents of low and high dielectric constant. In both compounds J 13CH increases algebraically in going to higher dielectric constant solvents. For CH 2 F 2 J 13CF increases algebraically for the same series of solvents. For CHF 3 J 13CF remains the same in two solvents and decreases algebraically in the third. The geminal HF coupling for both compounds is invariant in all solvents. A possible explanation of these results is suggested in terms of the electronic changes taking place in the solute molecules.

Carbon-13 Chemical Shift Assignments for the Bisulfite Adducts of Uracil, 5-Deuterouracil, 5-Fluorouracil and 5-Chlorouracil

Abstract Chemical shift assignments are made for the carbon atoms of the uracil-bisulfite adduct by use of specific labeling with deuterium and carbon-13. The signals of the analogous adducts from 5-chlorouracil and the pharmacologically important 5-fluorouracil are assigned.

Synthesis and stereochemical analysis of 2-amino-1,2,3,4-tetrahydro-1,4-methanonaphthalene-2-carboxylic acid, a conformationally rigid phenylalanine derivative

A rigid phenylalanine analogue, 2-amino-1,2,3,4-tetrahydro-1,4-methanonaphthalene-2-carboxylic acid (3) of unknown stereochemistry was obtained as the sole amino acid product from a Strecker reaction with 1,2,3,4-tetrahydro-1,4-methanonaphthalen-2-one (4). Compound (4) was initially treated with benzylamine and potassium cyanide to give 2-benzylamino-2-cyano-1,2,3,4-tetrahydro-1,4-methanonaphthalene (5), which was then converted into 2-benzylamino-2-carboxamido-1,2,3,4-tetrahydro-1,4-methanonaphthalene (6) by treatment with 70% sulphuric acid. N-Debenzylation of (6) by hydrogenolysis with 5% palladium-on-charcoal catalyst afforded 2-amino-2-carboxamido-1,2,3,4-tetrahydro-1,4-methanonaphthalene (7) which gave the acid (3) on heating in 10% sulphuric acid. A Stereochemical analysis of (3) by 1H n.m.r., 13C n.m.r, and auto-correlated two-dimensional n.m.r. spectroscopy, determined the structure to be 2-endo-amino-1,2,3,4-tetrahydro-1,4-methanonaphthalene-2-exo-carboxylic acid (1a). Treatment of 1,2,3,4-tetrahydro-1,4-methanonaphthalene-2-spiro-5′-hydantoin (9)[obtained from a Bucherer reaction with (4)] with aqueous barium hydroxide also afforded (1a) as the only amino acid product.