CH3CHCH2CH2 C O OH Br 5 4 3 2 1 δ γ β α

CARBOXYLIC ACIDS

Carboxyl group:

O

C OH

Nomenclature ¡ª

Common Name

formic acid,

acetic acid,

propionic acid,

butyric acid,

valeric acid,

caproic acid,

Structure

H-COOH

CH3-COOH

CH3CH2-COOH

CH3(CH2)2-COOH

CH3(CH2)3-COOH

CH3(CH2)4-COOH

IUPAC

methanoic acid

ethanoic acid

propanoic acid

butanoic acid

pentanoic acid

hexanoic acid

Positions along the chain are indicated by Greek letters

(common names) or numbers (IUPAC).

Br

O

CH3 CHCH2CH2 C OH

5 4 3 2

1

¦Ä ¦Ã ¦Â ¦Á

¦Ã-bromovaleric

acid

4-bromopentanoic acid

Dicarboxylic acids ¡ª

Structure

HOOC-COOH

Common Name

oxalic acid,

IUPAC

ethanedioic acid

HOOC-CH2-COOH

malonic acid,

propanedioic acid

HOOC-(CH2)2-COOH succinic acid,

butanedioic acid

HOOC-(CH2)3-COOH glutaric acid,

pentanedioic acid

HOOC-(CH2)4-COOH adipic acid,

hexanedioic acid

Aromatic acids ¡ª

O

C

O

OH

benzoic acid

C

C

O

C

OH

O

C

OH

OH

O

O

C

OH

O

isophthalic acid

phthalic acid

OH

C

OH

terephthalic acid

Salts ¡ª

Name cation followed by

acid name with -ic

changed to -ate, eg

Na+ -O

C

O

2

sodium benzo ate

Physical Properties ¡ª

Lower molecular weight acids are soluble in H2O:

hydrogen bonding. Usually soluble in organic solvents.

Sodium and potassium

salts of lower molecular

weight acids are soluble in

H2O and not soluble in

organic solvents of low

polarity. The salts of longchain carboxylic acids are

soaps. Sodium and

potassium soaps form

micelles in water.

A Micelle

Carboxylic acids form dimers (pronounced die'-mers) in

the liquid phase --O

H O

R C

C R

These dimers also

O H

O

exit to some extent

in the gas phase,

consequently, carboxylic acids have high boiling points

for a given molecular weight.

3

Acidity ¡ª

O

O

+

R C

+ H 2O

R C

+ H3O

O-

O H

O

O

R C

OO

Keq =

H3O

+

R

OO

Ka =

H2O

R C

+

C

R

H3O

C

O H

O H

pKa = -log K a

Compare acidity of carboxylic acids with alcohols:

CH3CH2OH

CH3CH2O- + H+, Ka ~ 10-16

CH3COOH

CH3COO- + H+, Ka ~ 10-5

4

Reason ¡ª

Carboxylate anion is more stable compared to

carboxylic acid than alkoxide ion is compared to alcohol.

Neither alcohol nor alkoxide ion are stabilized by

resonance, but the

situation is different

for a carboxylic acid

O

O

and its anion;

R C

R C

in this case the

O H

O H

anion is stabilized

more important

less important

more than the acid:

O

O

R

R

C

C

O

O

equally important

Substituent groups ¡ª

Those which stabilize the anion more than its

conjugate acid (electron withdrawing) increase acid

strength. Those which destabilize anion more than acid

(electron donating) decrease acid strength.

5

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