The other three hydrocarbons in the group-QC, PPL, and NBA -are saturated hydrocarbons as they possess solely C-C single bonds. Hydrogenation of the C=C double bonds in NBD results in the formation of NBN, where one C=C bond is saturated, and NBA, where both C=C bonds in NBD are saturated. Quadricyclane (QC) and norbornadiene (NBD) are isomers, whereas [2.2.1]propellane (PPL) is an isomer of NBN. As a result, this group of hydrocarbons is also liquid organic hydrogen carriers.