18.2.3 Solvent Effects on Organic Base Strength

Question 1

In gas phase, pKa of acetic acid is estimated to be 130 (Ka = 10−130 ). In contrast, pKa of acetic acid in aqueous solution is 4.76. Which of the following is an explanation for the difference?

Answer 1

All of these are good explanations.

Question 2

Acetic acid is a stronger acid in water than it is in methanol. Why?

Answer 2

Water molecules are smaller than methanol molecules.

Question 3

Amines have a lone pair of electrons on the nitrogen. Because of this, amines are both

Answer 3

basic and nucleophilic

Question 4

If solvation is poor, the base will be _____

Answer 4

unstable

Question 5

What should you examine when asked to compare bases?

Answer 5

All of the above

Question 6

Organic chemists use a sort of chemical short hand when drawing the structural formulas for organic compounds. What is one way of writing the complete formula for the following cation?

Answer 6

C7H7+

Question 7

In water, the primary amines such as methylamine, ethylamine, propylamine, and isopropylamine all have approximately the same pKb (about 3.4). What is the best explanation for this phenomenon?

Answer 7

The chemistry of amines is dominated by the lone pair on nitrogen.

Question 8

What is the steric number for ClF3?

Answer 8

5

Question 9

Morphine alkaloids are one example of a large group of biologically active amines that are extracted from a poppy, Papaver somniferum. How is it possible for alkaloids to penetrate a membrane and enter the brain?

Answer 9

In solution, the nitrogen atom is protonated.

Question 10

Some amines with more than six carbon atoms are not soluble in water. However, they will dissolve in dilute solutions of HCl. What is an explanation for this?

Answer 10

All of the above