Asymmetric reactions. XLVII. NMR-shift differences of enantiotopic proton signals in some alkylarylmethanols induced by tris[3-trifluoroacetyl-(+)-camphorato]europium(III)

Correlation of configuration of chiral secondary carbinols by use of a chiral lanthanide nuclear magnetic resonance shift reagent

“…It may be significant that the three examples with negative ß-s values for the carbinyl proton signals were substituted tert-butylcarbinols (methyl, n-butyl, and phenyl). These limited results indicate that a reliable configurational correlation for secondary carbinols, L1CHOHL2, in general cannot be based on the ß-s value for the proton on the carbinyl carbon, contrary to the suggestion of Cervinka, et al 15 However, the uniformly negative ß-s values for the proton signals on the Li and L2 substituents, when observable, indicate that the correlation of these signals with configuration may be general. Such a correlation should prove reliable and valuable when applied within a closely related series and with due consideration for the nature of the substituent groups.…”

Use of achiral shift reagents to indicate relative stabilities of diastereomeric solvates

“…As is apparent from Table I, the chemical shifts at Ci and C2 of 1 are similar to those of acrylic acid (5 Ci 128.0, C2 131.9).18 Also, the shifts in the other alkenylboranes show an analogous trend to those in a,/3-unsaturated carbonyl compounds, where the contribution of enolate form is important (eq 3). [18][19] ^X=C-C-…”

“…However, 13C NMR spectra have not as yet been obtained, despite the superior advantage that their chemical shifts can more directly provide insight into the bonding situations. [18][19] Alkynylboranes may also exist in the mesomeric allenyl form (eq 2),3a though to our knowledge there is no litera--C=C-B^* -*--C=C=B^ ( 2) ture evidence for such B-C bonding. In this paper, we report in full on the 13C NMR spectra and the bonding situation of alkenyl-and alkynylboranes.…”

“…Such contributions further complicate the assignment of absolute configuration through the use of chiral lanthanide shift reagents. [16][17][18][19] One obvious application for NMR experiments of this kind is the screening of compounds potentially useful as chiral stationary phases for the direct chromatographic resolution of enantiomers. The chiral compound being screened need not be capable of inducing type A nonequivalence for this approach to succeed.…”