The difference in chemical behavior of the three isotopes of hydrogen is mainly caused by the difference in their masses, which in turn influences the vibrational motions and the zero-point vibrational energies. Thus, from a measurement of an isotope effect in some property, one can make deductions about the shape of potential energy surfaces. This has been extensively exploited for elucidating chemical reaction paths from kinetic data.1 Here we report the usefulness of , 2H, and 3H NMR as a means of studying the shape of the potential energy surface in the vicinity of the equilibrium position.Primary isotope effects2 of the NMR chemical shifts of 2H and 3H in organic compounds are usually very small, in the case of 3H usually <0.03 ppm for tritium bound to sp2-or sp3-type carbons.3-4 Exceptions to this general rule are systems with relatively strong hydrogen bonds, for which deuterium isotope effects, ( , 2H), as large as 0.6 ppm have been found.5-7 We have previously reported the results of a systematic NMR study of the deuterium isotope effect, ( , 2H), in a series of systems all containing hydrogen bonds of the type O-H-O.6 A correlation between the isotope effect and the value of the chemical shift, 5(1H), was observed for the hydrogen-bonded nucleus.The only conceivable source of isotope effects on chemical shifts within the Born-Oppenheimer approximation lies in the isotopes mass dependence of vibrational motion. The quantities that determine the magnitude are the vibrational wave functions, f, for the ground state (and possibly low-lying excited vibrational states) and the variation of the chemical shift, ,

Background: Isotretinoin has been proven to be an effective treatment for acne vulgaris. The enclosed package insert with isotretinoin suggests weekly/biweekly laboratory testing (hepatic functions and lipid analysis) but fails to recommend the needed action levels for abnormalities. Methods: We provide a statistical analysis of a retrospective study of 141 individuals’ course of therapy on isotretinoin and their laboratory blood analysis results. Results: Very few statistically significant elevations in liver enzymes or lipid profiles occurred. More importantly, in only 1 case did these elevations warrant the discontinuation of therapy. Conclusion: The data presented here support the conclusion that limited blood testing should be performed for most patients and that more complete blood testing be done only for those patients with a significant response in liver enzymes, cholesterol or triglycerides. A set of guidelines is proposed for the practicing physician to interpret blood test results.

at 3.15 and 2.58. From the ratio of the N-methyl protons the ratio of XIV to XV at -20°was 9:1.Rapid heating to +70°c aused coalescence14 of the Nmethyl peaks in each compound, leading to two broad peaks at 3.50 and 2.66. Heating for 2 hr. caused a decrease in the 3.50 band in favor of the 2.66 band. At room temperature, the equilibrium ratio of 3.50 to 2.66 was about 3:1, in agreement with the ratio of rate constants from the ultraviolet equilibrations above.

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