A New Method for Determining Enantiomeric Excess, where the Sample Serves as its Own Reference

Abstract

characterized spectroscopically. On the basis of the 360-MHz H-NMR and 90-MHz "C-NMR spectral4] and the result of decoupling experiments the trimers were assigned to the structures la and l b . In both isomers the cyclopentene ring bound to the norbornane system is oriented in the endo position. A n l a l b Ill a) J . Falbe, U. Hasserodt: Katalvsaforen. Tenside und Mineralolodditiue.

Group IVA organometallic reagents. 2. Enantiomeric purity determination of 1,2-diols through NMR spectroscopy without chiral auxiliaries

“…Further Considerations. Focusing on those cases where dimers are the dominant species, the treatment developed in Appendix section II can be used to (1) obtain information on the helero/ homodimer distribution in the present systems from the analysis 4 (eq A20 and A21), (g) 2.5, (h) 1, (i) 0.4, (j) 0.04, and (k) 0.004. of the chemical shifts and (2) establish criteria to predict whether a system should exhibit self-discrimination.…”

“…Calculated chemical shifts vs. ee for nuclei in the R and S enantiomers at various exemplificative K values according to (A16) and (A17). K values are (a) 4000, (b) 400, (c) 40, (d) 16, (e) 6, (f)4 (eq A20 and A21), (g) 2.5, (h) 1, (i) 0.4, (j) 0.04, and (k) 0.004.…”

Expansion of the Concept of Nonlinear Effects in Catalytic Reactions Beyond Asymmetric Catalysis

“…In a seminal study they could demonstrate the influence of these interactions on the outcome of the stereoisomeric distribution of the products of stoichiometric reactions. Related observations followed in subsequent years but the first systematic study using mathematical models to explain the effect of non‐enantiopure substrates on the enantiopurity of the products only emerged in 1985 . The term nonlinear effect (NLE) was later coined by Kagan and co‐workers and was defined as “the nonlinear dependence of the product enantiopurity on the enantiopurity of a chiral auxiliary utilized in either asymmetric catalysis or asymmetric synthesis”.…”

A Protocol for NMR Analysis of the Enantiomeric Excess of Chiral Diols Using an Achiral Diboronic Acid Template

“…Using this method it is not possible to define which enantiomer is in excess.) A range of different achiral bifunctional templates have been developed that enable the ee of chiral alcohols, − thiols, − amines, , amino esters, phosphiranes, and carboxylic acids − to be accurately determined. Further to these reports, we now describe a new Horeau based NMR protocol that employs an achiral bis -boronic acid template to determine the ee of chiral diols.…”