Topic 15: nitrogen compounds Flashcards
(15 cards)
1
Q
Describe structure of amine
A
- Trivalent sp3 nitrogen + lone pair
- Trigonal pyramidal geometry
- N = e- rich = good nucleophile
2
Q
Classification of amines
A
- Ammonia = NH3
- Primary = NRHH
- Secondary = NRRH
- Tertiary = NR3
> More alkyl groups = donate e- density
> e- donation = N more nucleophilic
3
Q
Describe amine odours
A
- Small = fishy
- Diamines = rotten e.g. cadaverine
4
Q
Describe solubility in amines
A
- N: = allows formation of H-bonds with H2O
- Amines less than 5C = water soluble
5
Q
Why does the pKa for the tertiary amine not decrease?
A
- Weaker base = to react with H2O to produce OH- ions
- Increasing methyl groups = decreases solubility = less complete reaction = not hydrated properly
5
Q
Describe alkalinity of amines
A
RNH2 + H2O→ RNH3+ + OH-
- Nucleophiles = weak base
- Lone pair = chemical reactivity
- Determined using Kb/pKb
- High pKb = weak base
- Low pKb = strong base
6
Q
How to measure basicity from pKa
A
- Find Ka of conjugate acid = pKa of it
- Low pKa = weak base
- High pKa = strong base
7
Q
Why does pKa decrease when F is added to amine?
A
- F = draws e- density away from N = less e- rich = weaker base
- Closer the F to N = e- withdrawl stronger = base weaker
8
Q
Are amides basic?
A
- 2 resonance forms = lone pair N form + positive N form = less e- rich = neutral not act as base
9
Q
Give ways to synthesize amines
A
1) Reduction of amides
2) Reduction of nitriles
3) Reduction of nitro-compounds
10
Q
Describe reduction of amines
A
- Convert C=O → CH2
- Wolff-Kishner reaction
- NH2NH2/KOH
11
Q
Describe reduction of nitriles
A
- Convert C≡N → CH2NH2
- LiAlH4
12
Q
Describe reduction of nitro compounds
A
- Convert NO2 →NH2
- H2 gas/NaBH4/LiAlH4
13
Q
Describe Hofmann rearrangement
A
- Complete elimination of C=O group of amide → amine
14
Q
Describe Hofmann elimination
A
- Remove NH2 from amine = alkene
- Anti-Zaitsev
