How does shape affect London dispersion forces?

1 Answer
anor277
Oct 15, 2016

Lomger chain molecules tend to have more dispersion forces between molecules.

Explanation:

The best illustration of this principle might be given by the respective boiling points of #"neopentane, "(H_3C)_4C#, and #"n-pentane"#, #H_3C-CH_2CH_2CH_2CH_3#.

#"Neopentane"# has a boiling point of #9# #""^@C#; #"n-pentane"# has a boiling point of #36# #""^@C#. This difference in volatility is dramatic, yet both materials are isomeric pentanes with a general formula of #C_5H_12#. Because #"n-pentane"# is a long chain molecule, it has greater opportunity for intermolecular interaction between molecules, and thus greater dispersion forces and boiling point. #"Neopentane"# is a heavily branched alkane, whose shape does not allow branch to branch interaction.

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