N.S. Bhacca

Solvent effects in NMR spectroscopy—III : Chemical shifts induced by benzene in ketones

Abstract Solvent shifts (Δ CDCl 3 C 6 H 6 = δ CDCl 3 − δ C 6 H 6 ppm) are reported for a number of methyl- and methoxy-substituted quinones. In the anthraquinones examined, a C-1 methyl group undergoes only a small upfeld shift in benzene (0·06–0·17 ppm), whereas a C-2 or C-3 methyl group suffers a much larger upfield shift (0·52–0·60 ppm). These effects are only slightly modified by the presence of adjacent methyl groups. In contrast, the shifts observed for “isolated” C-1 or C-2 methoxy substituents in anthraquinones may be greatly modified in 1,2-dimethoxy or 1,3-dimethoxy-derivatives, reflecting the greater electronic interaction between the polar substituents. Solvent shifts support the previously assigned differences in stereochemistry and conformation between isoleutherin, eleutherin and a related system derived from the aphins.

Proton magnetic resonance spectra at 220 MHz of amino acids, porcine and bovine insulin and the A and B chains of bovine insulin

Abstract Proton magnetic resonance (PMR) spectra of 21 commonly occurring amino acids dissolved in CF 3 COOH or CF 3 COOD were recorded and analyzed in terms of proton chemical shifts, relative to (CH 3 ) 4 Si (TMS) as internal standard, and proton spin-spin coupling constants. The results were used for an analysis of PMR spectra of insulin and the individual A and B chains (as S -sulfonates), all dissolved in CF 3 COOH or CF 3 COOD. In the unusually high magnetic field applied (ca. 50,000 oersteds) large chemical shifts are found. Resonances from specific protons in arginine, alanine, asparagine, glycine, histidine, lysine, phenylalanine, threonine, and tyrosine residues are observed separately in single recordings. The γ-CH 2 protons of glutamic acid and glutamine residues form one separate band at 2.70 ppm, the CH 3 protons of leucine, isoleucine, and valine form another separate band at 1.00 ppm. Only proton resonances from cysteine, proline, and serine residues give no easily accessible evidence of their presence but they contribute significantly to the intensity versus chemical shift integrals.

Solvent effects in NMR spectroscopy—II : Solvent shifts in some steroidal sapogenins

Abstract The NMR spectra of a number of steroidal sapogenins have been determined employing both benzene and deuterochloroform as solvents. The Δ value (δCDC13 − δC6H6) for a specific proton is dependent upon the location of the proton relative to polar sites in the molecule. Solvent shifts can therefore be of great utility in structural and stereochemical problems.

The configuration and conformation of cularine

Abstract The absolute configuration of cularine has been shown to be d (= R) from the ORD of its hydrogenolysis product (VIII). The hydrochloride, methiodide and O-acetate of VIII showed a complete reversal of the long-wavelength Cotton effect and CD maximum at 290 mμ, while the short-wavelength Cotton effects at 226 and 210 mμ remained unaffected. This reversal is attributed to steric hindrance to rotation of the 2′-substituted benzyl moiety. NMR spectra at 100 mc/s permit the assignment of one of the 3 possible bent conformations to cularine.

The NMR spectra of taxinine and its derivatives

Abstract The 60 and 100 Mc NMR spectra of taxinine and several of its more important derivatives are assigned and discussed.