High-resolution PMR

Proof of structure for 9A ls provTdedljy the high resolution pmr spectrum of the corresponding Cjfi monobenzoate and comparison with spectra of the 24,25-dimethyl spiro-ketals kindly provided by Professor D. Williams of Indiana University. Based on spin decoupling experiments, absorptions due to H-17 and H-19 are... 

High-resolution nuclear magnetic resonance spectroscopy, especially 13C NMR, is a powerful tool for analysis of copolymer microstructure [Bailey and Henrichs, 1978 Bovey, 1972 Cheng, 1995, 1997a Randall, 1977, 1989 Randall and Ruff, 1988], The predicted sequence length distributions have been verihed in a number of comonomer systems. Copolymer microstructure also gives an alternate method for evaluation of monomer reactivity ratios [Randall, 1977]. The method follows that described in Sec. 8-16 for stereochemical microstructure. For example, for the terminal model, the mathematical equations from Sec. 8-16a-2 apply except that Pmm, Pmr, Pm and Prr are replaced by p, pi2, p2j, and p22. 

High resolution proton magnetic resonance (PMR) spectra were recorded on a Perkin-Elmer R-10, 60-megacycle per second spectrometer fitted with a decoupling unit, a temperature probe, and a computer averaging attachment. Unless specified otherwise, spectra were obtained at 33.5°C. Chemical shifts in the high resolution NMR spectra are expressed as usual in parts per million relative to the protons of tetra-methylsilane at 10 p.p.m. (t scale). 

Replacement of the organic solvent by D2O yielded multi-lamellar structures with no high resolution characteristics. Sonica-tion of these suspensions led to the formation of single bilayered vesicles which contained either A -THG or CBD. In these vesicles no signals from the cannabinoid protons could be detected at concentrations of A -THC or CBD twice as high as those for which PMR signals are easily determined in CDCl solution (Fig. IB). 

The different molecular shapes of diastereoisomeric diketopiperazines allows their ready separation on GLC columns. Whereas with most monocyclic diketopiperazines the dl compounds have shorter retention times than the ll isomers, the reverse is true for perhydro-1,4-dioxopyrrolo[l,2-a]pyrazines. The high degree of diastereoisomeric resolution of these compounds has been studied on a variety of columns. As diastereoisomeric diketopiperazines are more readily separated and studied as their iV-methyl derivatives, GLC and PMR data have been collected for cyclo-L-prolylsarcosine. ... 

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