Jean-Marie Bernassau

Longitudinal relaxation times and structure elucidation—I : Fatty acids and esters

Abstract The 13C relaxation times of several fatty acids and esters were measured. The values obtained can be used for assigning the carbon resonances or for locating the double bond along an alkyl chain.

Choice of delay time sequence in spin-lattice relaxation time measurements by inversion-recovery

The effect of the choice of the τ sequence in the inversion-recovery experiment is examined. The uncertainty in the value of T1 can be related to a function F of T1, the pulse interval delay, and the τis. Minimization of the function for a range of T1s yields optimized sequences of τis for the measurement of any T1 in the range. For the same length of experiment, the use of optimized sequences rather than intuitive sets of τis results in a 20 to 50% precision improvement in the determination of T1 values. In other words, a given precision in T1 requires a 50 to 100% longer experiment when using intuitive τis. Indeed, a simple formula is derived that relates the uncertainty in T1 to the signal/noise ratio of the fully relaxed spectrum and thus permits one to estimate beforehand the time necessary to achieve a given precision.

Circular dichroism of olefins—IV1: A semiquantitative prediction of the intensity of the cotton effect of allyl alcohols and ethers

Abstract A semi quantitative prediction of the intensity of the Cotton effect of a few allyl alcohols and ethers in the steroid and diterpene series has been derived. It relies on a calculation of the weight of the various conformations and on the allylic bond polarization model.

Center of mass displacement and relaxation times of linear alkynes

Abstract The carbon-13 chemical shifts and relaxation times of various linear alkynes have been measured. Complexation of these compounds with dicobalt octacarbonyl induces changes in δs and T1s. Unambiguous assignments were obtained from deuterium labelled octynes. The T1 variations result from the displacement of the center of mass of the aliphatic chain. They are systematic and can thus be used for assignment purposes.

RuCl3, NaOH-catalyzed isomerization of allylic alcohols to saturated ketones: Part II Regiochemistry

Abstract The RuCl 3 , NaOH-catalyzed isomerization of allylic alcohols to saturated ketones is shown to occur by an intramolecular 1,3-hydrogen shift. The rate-determining step does not involve cleavage of an allylic carbon-hydrogen bond.