Ch 20: Carboxylic Acids / Nitriles
conceptual points
Version 1.0:
Marc Anderson
Dept of Chemistry and Biochemistry
SF State University
[marc@sfsu.edu]
1
[#1] Naming
• “xxx-ane”  “xxxx-anoic acid”
ethanoic acid
common names: (acetic acid)
propanoic acid
(propionic acid)
or
 “xxx-anenitrile”
butanoic acid
(butyric acid)
pentanoic acid
(valeric acid)
• Carboxylic acids take “highest priority” in naming
3-chloro-4-methylhexanoic acid
2-bromo-hexanoic acid
(S)-2-bromopropanoic acid
4-bromo-2-hydroxybenzoic acid
2,3-difluoro-hexanenitrile
2
[#1] Naming
• Common names:
formic acid
benzoic acid
oxalic acid
citric acid
tartaric acid
calcium oxalate
(most common
constituent of
kidney stones!)
(D)(-)-tartaric acid:
(L)(+)-tartaric acid:
Meso tartaric acid:
(not present naturally)
3
[#2] Structure and Properties of acids
• Formic acid, along with most carboxylic acids, is planar
(and the carbon is sp2 hybridized)
4
[#2] Structure and Properties
• Carboxylic acids are hydrogen bond donors and acceptors
• … as such, they readily form “hydrogen bound dimers”:
• When extremely dilute, the dimer can be broken up
• Acids also extensively hydrogen bond to water and alcohols, and
are often aqueous soluble.
5
[#3] Biological acids and the HendersonHasselbach equation
• very briefly for now. addressed in biochemistry course
6
[#4] Acidic character of RCO2H
• Carboxylic acids readily dissolve in water:
• Relative acidity (low pKa) due to resonance stabilization of
conjugate base
7
[#4] Acidic character of RCO2H
• Nearby electron-withdrawing groups enhance acidity!
(… and the effect
is distance
dependent!)
8
[#4] Acidic character of RCO2H
• Why? Inductive stabilization of the conjugate base!
• Therefore, lower pKa value! (0.23) than normal.
9
[#4] Acidic character of RCO2H
• This also occurs for substituted benzoic acids:
• Why? consider the conjugate base !
10
[#5] Spectroscopy of acids / nitriles
• By molecular formula:
-
the hints are: two oxygens and a degree of unsaturation
nitriles: one nitrogen, and two degrees of unsaturation
• By 1H NMR:
- the hint is: broad singlet at 10-12 ppm
• By 13C NMR:
- the hint is: a peak at 180-190 ppm
11
[#5] Spectroscopy of acids / nitriles
t
3H
8
O
7
t
2H
CH3
6
HO
5
4
3
2
p
2H
bs
1H
(disappears
with D2O)
h
2H
1
0
10
9
8
7
6
5
4
3
2
1
12
[#5] Spectroscopy of acids / nitriles
• Typical problems:
C7H14O2
C7H13N
1H
1H
NMR:
0.8 d
1.1 m
1.4 m
1.7 m
2.2 t
12 bs
6H
2H
2H
1H
2H
1H
NMR:
0.9 s 9H
1.6 t 2H
2.3 t 2H
13