For the molecular formula C5H12, there are three constitutional isomers. They are:1. n-Pentane: a straight-chain alkane with all five carbon atoms connected in a row. CH3-CH2-CH2-CH2-CH32. Isopentane also called methylbutane : a branched-chain alkane with a methyl group CH3 attached to the second carbon atom of a butane molecule. CH3-CH CH3 -CH2-CH33. Neopentane also called dimethylpropane : a branched-chain alkane with two methyl groups CH3 attached to the central carbon atom of a propane molecule. CH3-C CH3 2-CH3