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Conformational Analysis. 30‐A 1 H and 13 C NMR Stereochemical Study on N –Methyl–Substituted cis – and trans –Fused Octahydro–2 H –1,3– and –3,1–benzoxazines
Author(s) -
Pihlaja Kalevi,
Mattinen Jorma,
Fülöp Ferenc
Publication year - 1996
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199612)34:12<998::aid-omr8>3.0.co;2-7
Subject(s) - chemistry , epimer , conformational isomerism , derivative (finance) , stereochemistry , homogeneous , nuclear magnetic resonance spectroscopy , nmr spectra database , carbon 13 nmr , spectral line , molecule , organic chemistry , physics , astronomy , financial economics , economics , thermodynamics
The 1 H and 13 C NMR spectra of cis ‐ and trans ‐fused N ‐methyloctahydro‐2 H ‐1,3‐ and ‐3,1‐benzoxazines and their 2‐methyl derivatives were analysed. All trans ‐fused derivatives studied existed in biased double chair conformations with roughly equal contributions of the equatorial and axial N ‐methyl groups. Of the cis ‐fused isomers, both N ‐methyl‐octahydro‐2 H ‐1,3‐benzoxazine and its 2‐methyl derivative attain exclusively the O ‐ in conformation, whereas N ‐methyloctahydro‐2 H ‐3,1‐benzoxazine is not conformationally homogeneous but a ca . 3:1 mixture of the N ‐ in and N ‐ out forms at 198 K and a 7:3 mixture at ambient temperature. Similarly, the 2‐methyl derivative of N ‐methyloctahydro‐2 H ‐3,1‐benzoxazine was found to be a ca . 3:2 mixture of C‐2 epimers with the N ‐ in and N ‐ out conformations, respectively.