[php snippet=1]
Which amine has the highest boiling point?
Loading ...
Correct Answer: B. B.
The primary amines A and B can donate two hydrogen bonds and accept one (due to the lone pair on N). Generally, for compounds with the same functional group, the higher molecular weight compounds have a higher boiling point due to increased opportunity for intermolecular van der Waals (weak, but better than nothing) interactions. Of course, even though a periodic table is available during the exam with a click of a button, you do not need to calculate the molecular weight since you can quickly determine the number of carbons of the different N-containing structures which easily reveals B as the “heaviest.”
Helpful hint: If all other factors are the same, increased molecular weight means that it is harder to push that molecule into the vapor phase meaning the boiling point would be higher.
Today’s question has been brought to you by Gold Standard MCAT.
Get more passage-based questions at Gold Standard MCAT.
Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.
