Download Chemistry 2000 Review: quantum mechanics of

Chemistry 2000
Spring 2016
Organic bases
(Chapter 16, Sections 16.116.4, 16.7)
Tracey Roemmele
1
Organic bases (amines)
When you hear the term “organic base”, it’s generally referring to an
amine.
Amines are readily protonated by acids:
H
..
N
R
R
base
R
+
..+
H
O
H
acid
N
H
R
+
R
R
conjugate acid
+
H
..
O
..
H
conjugate base
The basicity of amines is due to the lone pair on the nitrogen atom which
makes all amines (R = H, alkyl or combination) Lewis bases.
2
Organic bases (amines)
We have seen one other functional group containing nitrogen. Why is an
amine considered a good base, but an amide is not?
The nitrogen atom of an amide is so weakly basic that the oxygen of the
carbonyl group will be protonated over it.
3
Quantifying basicity
H
N
H
H
+
H
N
H
pKa = 9.3
H3C
+
H
H
pKa = 10.6
4
Quantifying basicity
H
..
N
R
R
R
H
+
..
O
..
H
N
R
+
R
R
..
H
..
..
N
N
H
-.. O..
+
H
H
pKb = 4.7
H3C
H
H
pKb = 3.4
5
Calculating pH of a basic solution
6
Calculating pH of a basic solution
7
Amino acids: acid and base
..O ..
..
H
N
H
..
C
C
R
H
..O ..
H
H
N
H
O
..
+
H
C
C
R
.. .O
.. .
H
8
Amino acids: acid and base
9
Beyond water: implications of acid-base chemistry
H
C
H
H
.. . O.
+
..
H
C
H
H
.. .
..I .
H
C
H
H
..
O
..
H
C
H
.. + .. ..I ..
H
10
Beyond water: implications of acid-base chemistry
11