organic CHEM 291A

Chemistry 291A McCurdy

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Homework #6 Due November 17 at the beginning of class

Read and study Chapter 6, Karty; handout on chapter 6 Reminder: Don’t forget to do your electronic homework!!! Suggested problems from Hornback (Not to be turned in for a grade):

Chapter 6: 6.41, 6.42, 6.44, 6.45, 6.46, 6.51, 6.54, 6.55, 6.56, 6.59, 6.61, 6.63, 6.70, 6.75, 6.76

Learning Objectives: a. Write an acid-base reaction for any acid and base b. Recognize acid or base strengths from Ka or pKa values and use these to predict the

position of an acid-base equilibrium c. Predict and explain the effect of the structure of the compound on the strength of an

acid or a base. Group Problems due:

Note: Each person who participated in group discussion of the problems must sign the homework to be turned in. If you did not participate in the group discussion on that problem set, then you may not sign the answer sheet.

1. a. What is the conjugate base of each of the acids listed below (use the Bronsted

definition of acids and bases).

i. NH3 ii. H2O iii. H2 iv. H-C=C-H (acetylene, contains a triple bond) v. CH3OH vi. H3O

+

b. List the acids (i-vi) in order of increasing acidity c. List the conjugate bases of those acids in order of decreasing basicity d. The Ka of a carboxylic acid is 1.2 x 10

-12. What is its pKa? e. What is the Ka of an acid whose pKa = 10?

2. Acid HA has a pKa = 8. Acid HB has a pKa = 13.

a. Which is the stronger acid? b. If Na+A- and HB are mixed, will its equilibrium lie to the right?

3. Rewrite each of the following reactions using curved arrows and show all nonbonded

electrons and any relevant bonds. For a line structure (part c) add hydrogens to the molecules.

Chemistry 291A McCurdy

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CH3OH + HI CH3OH2 + Ia.

b. CH3NH2 + +HCl CH3NH3 Cl

+ HF + Fc. 4. a. Draw the products of the proton transfer reaction between these reactants:

O + OH

b. Draw the free energy diagram for this reaction indicating whether it is endothermic or

exothermic. Explain why the reaction is endothermic (or exothermic). 5. a. For the molecules below, rank the acidity of each of the types of protons (a-g) from

lowest to highest? Explain your ranking (the explanations must involve on relative charge stability).

C O

OHH3C + HO

a b

c d

e

f

g

b. Based on your answer to part a, use curved arrow notation to draw the mechanism of proton transfer of the most acidic proton to a basic atom on the other reactant. Please draw the products of the reaction. Don’t forget to add in any lone pairs and any relevant bonds.

6. For the following series of molecules, arrange them in order of increasing acidity.

Briefly explain why (using arguments based on relative charge stability).

OH F

OH OH

F OH

Cla.

b.

OH OH

O

OH

O

Cl

c.

Chemistry 291A McCurdy

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SH OHf.

OHNH2e.

OH

O S O

O OHg.

OH OHOHCld.