Branched alkanes are named as a straight-chain alkane with attached alkyl groups. In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. Then the alkene part is reduced to the alkane. The alkene monomer converts to a long, sometimes "very" long, alkane in the polymerization process. It is an unbranched alkane, a saturated hydrocarbon chain with no cycles. It is the substituent form of the alkane pentane. Cracking is the breakdown of a large alkane into smaller, more useful alkenes. Neopentane is the simplest alkane with a quaternary carbon, and has achiral tetrahedral symmetry. The hydrogen atoms of the alkane are progressively replaced by halogen atoms. Tetraethylmethane is a branched alkane with 9 carbon atoms. Heptane is an alkane of seven carbon atoms, with the chemical formula CH. The number of carbon atoms may be considered as the size of the alkane. Likewise, Raney nickel will remove the sulfur of thiophene to give a saturated alkane. The triene is hydrogenated to the saturated alkane, cyclododecane. It is the simplest alkane with a tertiary carbon.