The proton magnetic resonance spectra of hexahydropyrrolizine, its salts, its 3-methyl derivatives, and its methiodide

Abstract
The spectra are discussed and many assignments made from considerations of the bond anisotropies. Double resonance provided some checks and gave |Jgem| for the α-methylene protons of hexahydropyrrolizine. Over the range –70 to +190° hexahydropyrrolizine exists mainly, if not entirely, in the cis-fused form. The 3-endo-methyl derivative, however, shows rapid nitrogen inversion at room temperature, and only below –60° does it exist predominantly in the cis-fused form. Incidentally, the configurations of the two stereoisomers of 3-methylhexahydropyrrolizine were confirmed. The shielding of the methyl group in hexahydropyrrolizine methiodide is compared with that in the methiodides of cis-and trans-octahydroindolizine and of trans-octahydroquinolizine.

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