Cyclononene is a cycloalkene with a nine-membered ring, with two possible geometric isomers, denoted cis-cyclononene and trans-cyclononene, or (Z)-cyclononene and (E)-cyclononene.[1]
References
^Turner, Richard B.; Meador, W. R. (1957). "Heats of Hydrogenation. IV. Hydrogenation of Some cis- and trans-Cycloölefins". Journal of the American Chemical Society. 79 (15): 4133–4136. doi:10.1021/ja01572a042.