(ภาพ)
Another interesting effect seen in alkanes is that increased branching lowers an alkane’s boiling point. Thus, pentane has no branches and boils at 36.1 C, isopentane (2-methylpropane) has one branch and boils at 27.85 C, and neopentane (2,2-dimethylpropane)has two dranches and boils at 9.5 C Similarly, octane boils at 125.7 C, whereas isooctane (2,2,4-trimethylpentane)boils at 99.3 C. Branched-chain alknes are lower-boiling because they are more nearly spherical than straight-chain alkanes, have smaller surface areas, and consequently have smaller dispersion forces.
3.6 Conformations of Ethane