Organic Chemistry
Organic Chemistry
12th Edition
ISBN: 9781118875766
Author: T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder
Publisher: WILEY
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Chapter 22, Problem 45P

Chapter 22, Problem 45P, 22.45	
	

	The  NMR data for the two anomers included very comparable peaks in the 2.0–5.6 region

The 1 H NMR data for the two anomers included very comparable peaks in the δ 2.0–5.6 region but differed in that, as their highest δ peaks, anomer V had a doublet at δ 5.8 (1H, J = 12 Hz) while anomer VI had a doublet at δ 6.3 ( 1 H ,  J = 4   H z ) .

(a) Which proton in these anomers would be expected to have these highest δ values?

(b) Why do the signals for these protons appear as doublets?

(c) The relationship between the magnitude of the observed coupling constant and the dihedral angle (when measured using a Newman projection) between C−-H bonds on the adjacent carbons of a C−-C bond is given by the Karplus equation. It indicates that an axial–axial relationship results in a coupling constant of about 9 Hz (observed range is 8–14 Hz) and an equatorial–axial relationship results in a coupling constant of about 2 Hz (observed range is 1–7 Hz). Which of V and VI is the αa anomer and which is the β anomer?

(d) Draw the most stable conformer for each of V and VI.

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