Jump to ContentJump to Main Navigation
The Assignment of the Absolute Configuration by NMR using Chiral Derivatizing AgentsA Practical Guide$
Users without a subscription are not able to see the full content.

Josi M. Seco, Emilio Quiqoa, and Ricardo Riguera

Print publication date: 2015

Print ISBN-13: 9780199996803

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780199996803.001.0001

Show Summary Details
Page of

PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 07 March 2021

Assignment of the Absolute Configuration of Monofunctional Compounds by Single Derivatization

Assignment of the Absolute Configuration of Monofunctional Compounds by Single Derivatization

Chapter:
4 Assignment of the Absolute Configuration of Monofunctional Compounds by Single Derivatization
Source:
The Assignment of the Absolute Configuration by NMR using Chiral Derivatizing Agents
Author(s):

Josi M. Seco

Emilio Quiqoa

Ricardo Riguera

Publisher:
Oxford University Press
DOI:10.1093/oso/9780199996803.003.0007

The procedures shown in Chapter 3 allow the determination of the absolute configuration of several classes of compounds (Chapter 1, Figure 1.18), but they require the preparation of two derivatives and the comparison of their NMR spectra. Alternative methods have been developed for secondary alcohols and α-chiral primary amines. These are particularly suited for those cases where the amount of the available sample is low, and they require the preparation of only a single derivative [41–43, 55–56, 165]. There are three different approaches to using only a single derivatization to perform the assignment of those substrates [13, 165]. The first two are based on a controlled conformational change that is produced either by modification of the probe temperature [41, 165] or by selective complexation [42, 55, 56, 165]. The third one is based on the differences observed between the chemical shifts of the free alcohol and those of the 9-AMA ester derivative [43, 165]. In general, these single-derivatization procedures are limited to 1H NMR. Because the shift differences observed in 13C NMR are quite small, they produce insignificant Δδ values, and therefore the signs are not sufficiently accurate to produce a safe assignment [72]. Explanations and examples of applications are presented in the remainder of this chapter. For the assignment of secondary alcohols, a simple approach based on the use of a single MPA ester has proven to work very well [41, 165]. It is based on the controlled shift of the conformational equilibrium between the two main conformers (sp/ap) that were described in Chapter 1 for the MPA esters of secondary alcohols [36, 37]. Thus, for the assignment, it is only necessary to prepare either the (R)- or the (S)-MPA ester and then to compare the chemical shifts of L1/L2 in the spectra taken at room temperature and at a lower temperature [41]. Figure 4.2 presents a summary of the procedure and the graphical model expressing the ΔδT1T2 correlation between the sign and the stereochemistry for the assignment of secondary alcohols derivatized as (R)- or as (S)-MPA esters.

Keywords:   double derivatization, esterification shifts, low temperature NMR, primary amines, secondary alcohols

Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.

Please, subscribe or login to access full text content.

If you think you should have access to this title, please contact your librarian.

To troubleshoot, please check our FAQs , and if you can't find the answer there, please contact us .