Ch 19 - Amines

Question 1

What is the name of this molecule?

Answer 1

N,N-diethylaniline

Question 2

Name?

Answer 2

tertaethylammonium iodide

Question 3

Name?

Answer 3

N-butylpyridinium bromide

Question 4

Know these nitrogen heterocycles

Answer 4

Question 5

Know these nitrogen heterocylces

Answer 5

Question 6

Know these nitrogen heterocycles

Answer 6

Question 7

Why do tertiary amines have lower boiling points than primary and secondary amines of similar MW?

Answer 7

Tertiary amines have no hydrogen on the nitrogen, so there is NO hydrogen bonding.

Question 8

How do amines act as a Lewis Base or Bronsted-Lowry Base?

Answer 8

Amines are nucleophiles (Lewis Base) because of their LP that can form a sigma bond with an electrophile.

Therefore amines are nucleophiles.

Amines can accept a proton (H⁺) from a proton acid (like HCl).

Question 9

What types of substituents increase the basicity of amines?

Answer 9

Electron-donating groups increase the basicity of amines because they donate electrons toward the cation that forms when the amine picks up a proton/donates electrons (BLB/LB). This stabilizes the nitrogen cation.

Question 10

What are the two effects that stabilize ammonium ions in aqueous solution? In other words, what stabilizes the product of amines when they act as bases?

Use these two effects to explain why tertiary amines are NOT stronger bases than primary and secondary amines.

Answer 10

Inductive stabilization and solvation.

EDG’s stabilize via induction by providing electron density to the ammonium cation. So you would think tertiary amines are stronger because of more alkyl groups donating electron density.

However, tertiary amines stericly hinder water from solvating the ammonium cation. Ammonium ions are charged, so they are strongly solvated by water, but the more substituted the amine, the fewer water molecules that can get in a stabilize the cation.

Secondary amines balance inductive stabilization and solvation and are, therefore, slightly more basic than primary amines. But tertiary amines are less basic than primary and secondary with all other factors being equal.

Question 11

Is pyrrole more or less basic than aliphatic amines?

Answer 11

Pyrrole is a very weak base and less basic than most aliphatic amines.

This is because pyrrole is aromatic with N’s lone pair in a p orbital, contributing to the aromatic sextet.

If pyrrole’s N is protonated, it becomes sp³ and loses its aromaticity, unfavorable.

Question 12

Which is a better base, pyridine or piperidine?

Answer 12

Piperidine is a better base because its LP on N is sp³. sp³ orbitals have less s character and are not held as tightly by the nucleus.

Pyridine’s LP is sp² hybridized; therefore, its non-bonding electrons are more tightly held.

Nitriles have a non-bonding pair of electrons that are sp hybridized and are very weak bases (pK_b ~ 24).

Question 13

Are arylamines (anilines and their derivatives) weaker or stronger bases compared to aliphatic amines?

Why?

Answer 13

Arylamines are much weaker bases because resonance delocalizes the nonbonding electrons in the free amine.

In aniline, overlap between the aromatic ring and the orbital containing the amine’s lone pair stabilizes the lone pair and makes it less reactive.