✦ LIBER ✦
Compounds with bridgehead nitrogen. Part 72—NMR spectra and stereochemistry of 8,9,10,11,11a,11b,12,13-octahydro-7aH-quino [1,2-c][1,3]benzoxazines and perhydropyrido [1,2-c][1,3]benzoxazines. NMR chemical shifts of methylene group protons adjacent to a nitrogen atom
✍ Scribed by Trevor A. Crabb; Simon T. Ingate; Thomas G. Nevell; Steven Sumner
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 273 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
The positions of conformational equilibria in the four diastereoisomers of 8,9,11,11a,11b,12,13‐octahydro‐7a__H__‐quino [1,2‐c] [1,3] benzoxazines were investigated using ^13^C and ^1^H NMR spectroscopy. Comparison of the NMR chemical shifts of these isomers with those in the corresponding isomers of perhydropyrido [1,2‐c] [1,3]benzoxazine shows the effect on NMR shifts of fusion of the aromatic ring on to the fully saturated system. The Δδ values are discussed in terms of degree of overlap of the nitrogen lone pair orbitals with the aromatic π‐system.