monosubstituted alkene. (organic chemistry). An alkene with the general formula RHC=CH 2, where R is any organic group; only one carbon atom is bonded directly to one of the carbons of the carbon-to-carbon double bond.1  Facebook.2  Twitter.onosubstituted alkene. (organic chemistry). An alkene with the general formula RHC=CH 2, where R is any organic group; only one carbon atom is bonded directly to one of the carbons of the carbon-to-carbon double bond. 1  Facebook. 2  Twitter.