1,2-Oxazine chemistry. Part 6. Conformational analysis of cyclohexene and a heterocyclic analogue by 13C nuclear magnetic resonance spectroscopy

Abstract

The ¹³C n.m.r. spectra of twenty-six 3,6-dihydro-1,2-oxazines are reported. A multiple linear regression analysis of the substituent effects on the shifts of the ring carbon atoms gives results similar to those found with cyclohexene, suggesting conformational similarities between these ring systems. It is inferred from the results that alkyl groups at positions 3 and 4 in a cyclohexene-like system largely prefer the equatorial position.