Carboxylic Acids
−
Carboxyl group:
-CO2H, -COOH
R
O
H-bond acceptor
+
C
−
O
H
+
H-bond donor
Intermolecular forces: dipole-dipole, H-bonding
O
R
H
O
C
C
O
H
O
R
Pure carboxylic acids form
hydrogen bonded dimers
• very high boiling points
(higher than alcohols)
Carboxylic Acid Nomenclature
O
R
C
• Parent chain: longest containing carboxyl group (COOH) O
H
• Name of parent: replace “–e” with “–oic acid”
• Numbering starts at carboxyl carbon
– Priority: Carboxylic acid > aldehydes > ketones > alcohols

O
O
“hydroxy”
“oxo”
substituent
substituents
OH
3-oxobutanoic acid
O
(diabetes)
O
HO
O
OH
OH
propanedioic acid
(apples)
trans-3-methyl-2-hexenoic acid
(human armpits)
OH
O
O
OH
O
HN
O
CH3
aspirin
Tylenol
Can irritate your stomach
Gentle on the stomach
A carboxylic acid
Just an alcohol
Carboxylic Acid Reactions
• Acid-Base reactions (formation of carboxylate salts)
O
O
R
+
C
R
NaOH
OH
+
C
O
carboxylic acid + strong base

H2O
Na
carboxylate salt + water
Naming: cation, then anion (regular ionic compound)
Anion name: replace “–oic acid” with “–oate”
O
sodium hexanoate
O
Na
• Reduction to 1° alcohols
– Only LiAlH4 reduces carboxylic acids (not NaBH4 or H2/Pt)
O
LiAlH4
butanoic acid
OH
1-butanol
OH
What are the products?
O
O
OH
3-oxo-4-pentenoic acid
H2/Pt
NaBH4
LiAlH4
OH
O
OH
OH
O
OH
3-hydroxypentanoic acid
3-hydroxy-4-pentenoic acid
OH
OH
4-pentene-1,3-diol
Carboxylic Acid Reactions
• Certain molecules can attack the carboxyl carbon
and replace the –OH group
O
O
R
C
+
H
H−Nu
OH
R
C
+ H2O
Nu
H−Nu
Product
O
H-OR′
Alcohol
Ester
R
C
OR'
O
H-NH2
Amine
Amide
R
C
NH2
What do these flavors/smells have in common?
O
O
O
O
apricot
O
O
O
grape
pear
rum
O
O
O
O
H
O
NH2
O
banana
O
O
O
O
O
apple
orange
O
O
raspberry
OH
pineapple
wintergreen
O
Made from a carboxylic acid
and an alcohol
R
Esters
C
O
R'
Esters from Carboxylic Acids & Alcohols
• Nucleophilic substitution – a condensation reaction
O
R
O
H+
C
+
O
H
carboxylic acid
O
R'

R
C
O
H
+
+
alcohol

H 2O
R'
+
ester
water
• Reverse reaction = hydrolysis (“water-splitting”)
O
R
C
+
O
ester
O
H+
H 2O

R'
+
R
C
+
O
water

H
carboxylic acid
O
R'
H
+
alcohol
Esters
O
O
R – C – O – R’
O
H H O
H
C C C O CH
H 3
from propanoic acid
methyl group
H H
an
ester
a carboxylic
acid
propanoic acid
An ester is similar to a carboxylic acid,
but the acidic hydrogen has been
replaced by an alkyl group (R)
methyl propanoate
Naming Esters
• Named as “alkyl alkanoates”
– Alkyl group first (from alcohol)
– Acid name: “-oic acid” changed to “-oate”
O
ethyl butanoate
O
(pineapple)
O
pentyl butanoate
O
(apricot)
O
1
O
3-methylbutyl ethanoate
3
2
4
(banana)
Naming Esters
O
O
O
R – C – O – R’
Name the following ester:
O
CH3CH2CH2C-O-CH2CH3
Step 1) the ester alkyl group (R’) = ethyl
Step 2) the acid (R) = butanoic acid
Step 3) the name = ethyl butanoate
Formation of an Ester
H H H O
H
C C C C O
OH
H +
H H H
butyric acid (butanoic acid)
H H
HO C C H
H H
ethyl alcohol
+
water
ethyl butanoate or ethyl butyrate (tastes and smells like pineapple)
D
O
Ester
CH3
O
H C O C CH3
Raspberry
R C O R'
H
H O
CH3
H C C O CH2 CH2 CH CH3
H
CH3
Banana
H O
H C C O CH2 (CH2)6 CH3
H
Orange
Ester
H O
O
H C C O CH2 CH2 CH3
H
R C O R'
Pear
H
H
C
H O
C
H C C O CH2 C
H
Peach
C H
C
H
C
H
Structural Isomers
• Draw all possible isomers of C3H6O2
Two oxygen's → carboxylic acids and esters