The infrared absorption spectrum of gelsemine indicates the presence of a carbonyl group. Reduction of the alkaloid with lithium aluminum hydride converts the carbonyl not to a secondary alcohol, but to a methylene group, thus indicating that the carbonyl is present in a lactamic grouping. The reduced base shows the properties of a substituted aniline. Since gelsemine has been shown to yield 3-ethylindole on dehydrogenation with selenium and since the N-atom involved in the lactamic group cannot be the strongly basic nitrogen, gelsemine must contain an oxindole grouping. Furthermore, 3-monosubstituted oxindoles are converted by lithium aluminum hydride to 3-substituted indoles, whereas gelsemine under the same conditions gives rise to a dihydroindole. Therefore, the alkaloid must contain a 3, 3-disubstituted oxindole grouping.