The conformational analysis of saturated heterocycles. Part LXVII. 2-Alkyl-3,6-dihydro-2H-1,2-oxazines and 3-alkyl-3,4-dihydro-1H-2,3-benzoxazines

Abstract

Low temperature n.m.r. studies of the title compounds indicate that nitrogen inversion is slowed. Peak area measurements show that 2-methyl substituents prefer the equatorial position by a factor of ca. 10 : 1 and 2-t-butyl substituents by a considerably larger factor. This considerable equatorial preference is due in part to lone pair–lone pair repulsion in the 2-axial conformers. The conclusions from n.m.r. are compared with measured and calculated dipole moments.