2 • Additional Problems
2 • Additional Problems
Fill in the multiple bonds in the following model of naphthalene, C10H8 (black = C, gray = H). How many resonance structures does naphthalene have? Draw them.
The following model is a representation of ibuprofen, a common over-the-counter pain reliever. Indicate the positions of the multiple bonds, and draw a skeletal structure (black = C, red = O, gray = H).
cis-1,2-Dichloroethylene and trans-1,2-dichloroethylene are isomers, compounds with the same formula but different chemical structures. Look at the following electrostatic potential maps, and tell whether either compound has a dipole moment.
Electronegativity and Dipole Moments
Which of the following pairs of structures represent resonance forms?
1,3-Cyclobutadiene is a rectangular molecule with two shorter double bonds and two longer single bonds. Why do the following structures not represent resonance forms?
Acids and Bases
The O–H hydrogen in acetic acid is more acidic than any of the C–H hydrogens. Explain this result using resonance structures.
Rank the following substances in order of increasing acidity:
Is tert-butoxide anion a strong enough base to react significantly with water? In other words, can a solution of potassium tert-butoxide be prepared in water? The pKa of tert-butyl alcohol is approximately 18.
Predict the structure of the product formed in the reaction of the organic base pyridine with the organic acid acetic acid, and use curved arrows to indicate the direction of electron flow.
Maleic acid has a dipole moment, but the closely related fumaric acid, a substance involved in the citric acid cycle by which food molecules are metabolized, does not. Explain.
Which of the following pairs represent resonance structures?
Carbocations, which contain a trivalent, positively charged carbon atom, react with water to give alcohols:
How can you account for the fact that the following carbocation gives a mixture of two alcohols on reaction with water?
The azide functional group, which occurs in azidobenzene, contains three adjacent nitrogen atoms. One resonance structure for azidobenzene is shown. Draw three additional resonance structures, and assign appropriate formal charges to the atoms in all four.
Phenol, C6H5OH, is a stronger acid than methanol, CH3OH, even though both contain an O–H bond. Draw the structures of the anions resulting from loss of H+ from phenol and methanol, and use resonance structures to explain the difference in acidity.
Thiamin diphosphate (TPP), a derivative of vitamin B1 required for glucose metabolism, is a weak acid that can be deprotonated by a base. Assign formal charges to the appropriate atoms in both TPP and its deprotonation product.
Which of the following compounds or ions have a dipole moment?
(a) Carbonate ion (CO32–) (b) (c)