rippinitez

10+ Year Member
5+ Year Member
Aug 20, 2007
206
0
0
Status
Pre-Dental
Kaplan indicates that the branching of alkanes decreases BOTH melting and boiling points.

However, in Chad's vid's he states that M.P. increases with branching. Any ideas as to which is correct?
 

Cool Beans

7+ Year Member
Apr 5, 2010
83
7
151
Status
Kaplan indicates that the branching of alkanes decreases BOTH melting and boiling points.

However, in Chad's vid's he states that M.P. increases with branching. Any ideas as to which is correct?
Chad's videos have it correct.
More branching decreases the surface area of a molecule which decreases the London Dispersion Forces resulting in a lower boiling pt.
But more branching makes molecules pack better into crystals which raises the freezing point (same as melting pt.).

Take the comparison of pentane and neopentane (2,2-dimethylpropane) which both have the chemical formula C5H12.

pentane m.p.=-130 C b.p.=36C
neopentane m.p.=-16.6C b.p.=9.5C

Neopentane is more branched and has the higher melting pt, but lower boiling pt.
 
Apr 14, 2010
54
0
41
Status
Pre-Dental
Can someone kindly give me the link to Chad's videos? Thanks in advance :)