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R C
O
O H
Carboxylic Acids
Carboxyl group: -CO2H, -COOH
Pure carboxylic acids form hydrogen bonded dimers
• very high boiling points (higher than alcohols)
H-bond donor
H-bond acceptor
+−
−
+
R C
O
O H
RC
O
OH
Intermolecular forces: dipole-dipole, H-bonding
Carboxylic Acid Nomenclature
• Parent chain: longest containing carboxyl group (COOH)
• Name of parent: replace “–e” with “–oic acid”
• Numbering starts at carboxyl carbon
– Priority: Carboxylic acid > aldehydes > ketones > alcohols
“hydroxy” substituent
“oxo” substituents
OH
O
trans-3-methyl-2-hexenoic acid(human armpits)
OH
O O
3-oxobutanoic acid(diabetes)
HO OH
O O
propanedioic acid(apples)
R C
O
O H
O
OHO
O
aspirin
OH
HN O
CH3
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)
• Reduction to 1° alcohols– Only LiAlH4 reduces carboxylic acids (not NaBH4 or H2/Pt)
carboxylic acid strong base carboxylate salt water
Naming: cation, then anion (regular ionic compound)
Anion name: replace “–oic acid” with “–oate”
sodium hexanoate
butanoic acid 1-butanol
R C
O
OH
R C
O
O Na
NaOH H2O+ +
+ +
O
O Na
OHOH
O LiAlH4
What are the products?
3-oxo-4-pentenoic acid
LiAlH4
H2/Pt NaBH4
OH
OOH
OH
OO
OH
OOH
OH
OH
3-hydroxypentanoic acid
4-pentene-1,3-diol
3-hydroxy-4-pentenoic acid
Carboxylic Acid Reactions
• Certain molecules can attack the carboxyl carbon and replace the –OH group
H−Nu
H-OR′ Alcohol
H-NH2Amine
Product
Ester
Amide
R C
O
OH
+ R C
O
Nu
+ H2O
R C
O
OR'
R C
O
NH2
H−Nu
OH
H
What do these flavors/smells have in common?
EstersR C
O
O R'
Made from a carboxylic acid and an alcohol
NH2
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OH
O
O
H O
O
banana
apricot
pear grape rum
wintergreen
orange
pineapple
apple
raspberryO
O
Esters from Carboxylic Acids & Alcohols• Nucleophilic substitution – a condensation reaction
O R'
H
R C
O
O H
R C
O
O R'
+ H2OH+
+
carboxylic acid alcohol ester water++
• Reverse reaction = hydrolysis (“water-splitting”)
H+
R C
O
O R'
+ H2O
ester water+
O R'
H
R C
O
O H
+
carboxylic acid alcohol+
Esters
An ester is similar to a carboxylic acid, but the acidic hydrogen has been replaced by an alkyl group (R)
H
OC C C
H
H
OHH
H
a carboxylic acid
H
OC C C
H
CH3
OHH
H
an ester
methyl propanoate
methyl group
propanoic acid
from propanoic acid
R – C – O – R’
O
O
O
O
O
Naming Esters
• Named as “alkyl alkanoates”– Alkyl group first (from alcohol)– Acid name: “-oic acid” changed to “-oate”
ethyl butanoate
O
O
pentyl butanoate
3-methylbutyl ethanoateO
O
(pineapple)
(apricot)
(banana)
1
2
3
4
Naming Esters
Name the following ester: CH3CH2CH2C-O-CH2CH3
O
Step 1) the ester alkyl group (R’) = ethyl
Step 2) the acid (R) = butanoic acid
Step 3) the name = ethyl butanoate
R – C – O – R’
O O
O
Formation of an Ester
H
OHC C C
H
OHH
H
C
H
H +
H
C H
H
H
C
H
HO
H
OC C C
H
OHH
H
C
H
H
+
H
C H
H
H
C
H
HOH
butyric acid (butanoic acid) ethyl alcohol
ethyl butanoate or ethyl butyrate (tastes and smells like pineapple)
water
Ester
H
C CH3
CH3
OH C
O
OR C
O
R'Raspberry
CH2 CH2H OC C
H
OH
CH
Banana
CH2 (CH2)6H OC C
H
OH
CH3
Orange
CH3
CH3
CH3
Ester
OR C
O
R'CH2 CH2H OC C
H
OH
CH3
Pear
Peach
CH2H OC C
H
OH C C
C C
C C
H H
H H
H
Structural Isomers
• Draw all possible isomers of C3H6O2
Two oxygen's → carboxylic acids and esters
