The solid state structures of the (-)-n-heptylcarbamate of geneseroline and its hydrochloride salt were determined by single crystal X-ray diffraction analysis. Both compounds gave crystals belonging to the orthorombic P2(1)2(1)2(1) space group with a = 27.597(7) A, b = 8.899(2) A, c = 9.290(2) A, V = 2281.5(9) A3, Z = 4, and R = 0.0682 for the base and a = 11.300(1) A, b = 8.3485(5) A, c = 24.141(2) A, V = 2277.3(3) A3, Z = 4, and R = 0.0482 for the salt. X-ray and 1H NMR analysis revealed that the base is a 1,2-oxazine derivative. The six-membered ring adopts a 4C1 chair conformation in the solid-state, whereas, in CDCl3 solution, it exists as a mixture of two possible chair conformers, 4C1 and 1C4, with the N-methyl group in the equatorial position (ratio approximately 75:25). The salt is an N-oxide derivative; the five-membered ring adopts different envelope conformations in the solid-state and in CDCl3 solution, suggesting a certain flexibility. In more polar solvents, the salt partially undergoes fast inversion at the tetrahedral nitrogen, giving rise to the corresponding epimer.