How is alkane mp affected by branching?


Junior Member
15+ Year Member
Feb 13, 2004
Fresno, CA
I could be getting this mixed up, so could someone please clear up the confusion. I know that increased branching is supposed to weaken Vanderwaals forces. It would make sense that this would decrease the mp since there are weaker intermolecular forces and hence not as high temp should be needed to break these weaker forces in going from solid to liquid. I swear EK says that it decreases bp and increases mp. Can someone confirm, does branching decrease or increase mp?


Registered Republican
7+ Year Member
15+ Year Member
Dec 4, 2002
branching decreases mp.

Melting points and boiling points are determined by the intermolecular forces of attraction between molecules in the solid and liquid states, respectively. For nonpolar molecules like alkanes, the main intermolecular forces of attraction are London dispersion forces. London dispersion forces increase with increasing number of carbon atoms and increase with the area of contact between neighbouring molecules. With respect to the latter, the area of contact depends on the shape, decreasing as branching increases in the molecule. Therefore, a straight-chain alkane has a higher boiling point than a branched alkane with the same number of carbons.
For polar compounds such as alcohols, amines, and carbonyl compounds, the important intermolecular forces are dipole-dipole attractions and hydrogen bonding. These generally lead to higher boiling points than for nonpolar molecules.

check out


7+ Year Member
15+ Year Member
Jan 27, 2004
This thread is more than 17 years old.

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.