Chemistry 2412
Clower
Assignment 3: Properties of Carboxylic Acids
10 points
The following assignment uses the Molecular Modeling Workbook and accompanying CD. Your
answers must be typed. Structures must be drawn neatly by hand or using ChemDraw.
1. The following questions refer to the molecular modeling problem 20-3: Intra and
Intermolecular Hydrogen Bonding.
a. Look at the electrostatic potential map for acetic acid. Which atom(s) is(are)
the most electron-rich? Which atom(s) is(are) the most electron-poor?
b. Based on your answers for (a), determine which atoms are most likely to form
hydrogen bonds with one another, and draw the structure of an acetic acid dimer.
c. Briefly explain why the boiling points of carboxylic acids are so much higher
than the boiling points of alcohols of similar molecular weight.
2. The following questions refer to the molecular modeling problem 10-6: pKa’s of
Alcohols.
a. Examine the electrostatic potential maps for methanol, ethanol, 2-propanol,
and trifluoroethanol. Rank these compounds from least to most acidic.
b. What correlations can you make between the structure of alcohols and their
acidity? Be specific.
c. Look at the electrostatic potential map for phenol. Is it a stronger or weaker
acid than the alcohols listed in (a)? Explain.
d. Compare the electrostatic potential map of 4-nitrophenol to that of phenol.
What affect does the nitro substitutent have on the acidity of the alcohol? Why?
e. Carboxylic acids are stronger acids than alcohols. Why?
f. Based on what you know about structure and acidity, which carboxylic acid
would you expect to have a lower pKa value, acetic acid or trifluoroacetic acid? Explain.
g. Substituents can also affect the acidity of benzoic acid. Rank the following
compounds from least to most acidic: benzoic acid, p-nitrobenzoic acid, p-
methoxybenzoic acid. Explain your ranking.
