Which of the following can hydrogen-bond with itself?

#(a)# butane
#(b)# acetone
#(c)# acetic acid

1 Answer
May 29, 2017

Should be #(c)#.


While it's true that acetone, #("CH"_3)_2"C"="O"# can hydrogen-bond with water, it can only form dipole-dipole interactions with itself.

https://upload.wikimedia.org/

Acetic acid, #"CH"_3"COOH"#, can hydrogen-bond with itself (very well, I might add!).

https://upload.wikimedia.org/

By recalling the relative intermolecular forces and their strengths...

London Dispersion #<# Dipole-Dipole #<# H-"bonding" #<# Ion-Dipole #<# Ion Pair

...and recalling that as intermolecular force strengths increase, molecules stick together more and vaporize less easily (corresponding to a higher boiling point), we would then have that:

  • since butane, #"CH"_3"CH"_2"CH"_2"CH"_3#, only has London Dispersion (being a hydrocarbon, a nonpolar molecule!), it has the lowest boiling point.
  • since acetone has dipole-dipole interactions with ITSELF, it has the second-highest boiling point.
  • since acetic acid hydrogen-bonds with ITSELF, it has the highest boiling point.

And we can't go without the data. From a quick Google search:

#-1^@ "C"# for butane
#56^@ "C"# for acetone
#118.1^@ "C"# for acetic acid

which follows the trend predicted above. Hence, the answer is #(c)#.