can anyone explain the relationship between branching, surface area & chain length of paraffins with their melting and boiling point?
Boiling pt. increases with increasing surface area of compound as this increases the tendency of molecules to interact and hence greater inter-molecular interaction. Boiling pt. also increases with increase in Dipole moment as it increases polarisation.
Thus, bp decreases with increasing branching and increases with increasing surface area. Chain length has no direct participation in this. But in case of two st. chain compounds, the one with longer chain will have greater bp due to greater molecular wt. While in case of two branched hydrocarbons, the one with minimal branching will have higher bp.
Mp depends upon packing fraction i.e. no. of molecules being packed in a unit volume. Packing fraction increases with symmetry of molecular structure. Thus, neopentane has greater mp than n-pentane due to symmetry of the compound. It has nothing to do with branching, or surface area. THOUGH IT ALSO INCREASES WITH INCREASE IN MOLECULAR WT.
Thus, bp decreases with increasing branching and increases with increasing surface area. Chain length has no direct participation in this. But in case of two st. chain compounds, the one with longer chain will have greater bp due to greater molecular wt. While in case of two branched hydrocarbons, the one with minimal branching will have higher bp.
Mp depends upon packing fraction i.e. no. of molecules being packed in a unit volume. Packing fraction increases with symmetry of molecular structure. Thus, neopentane has greater mp than n-pentane due to symmetry of the compound. It has nothing to do with branching, or surface area. THOUGH IT ALSO INCREASES WITH INCREASE IN MOLECULAR WT.
Thanx 4 d explanation.
visit http://www.chemguide.co.uk/atoms/bonding/vdw.html#top and clear all your doubts.
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