why boiling point of hydrocabans decrease with increase in branching
This is due to the weaker Van der Waals dispersion forces between branched organic molecules compared to straight chain molecules. Van der Waals dispersion forces are proportional to the surface area of the molecule.
For the same number of carbon atoms, branched molecules are more compact, with fewer atoms at the surface of the molecule able to interact with the atoms on the surface of other molecules
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