Announcements & Agenda (03/28/07)
Exam Results: 75% Ave, 100% High
Quiz next Wednesday (Chirality & Ch 13)
Will hand out HW practice on Monday
Today
 Chirality (12.6)
 Carboxylic acids (13.1, 13.2)
 Esters (13.3)
1
What to do if…
…this test didn’t go as planned…
Make a plan for preparing for the rest of 103




DO practice problems and study!!!
ATTEND weekly reviews!!!
REVIEW scores from assignments with Bob to
estimate grade
DO the extra credit assignment
VISIT BOB
2
Will Do Tollens’ Test on Friday
• Tollens’ reagent,
which contains
Ag+, oxidizes
aldehydes, but
not ketones.
• Ag+ is reduced
to metallic Ag,
which appears
as a “mirror” in
the test tube.
3
Chiral Molecules (12.6)
• Stereoisomers: have the same # of atoms connected
in the same order BUT are arranged differently in
space (just another kind of geometric isomer)
• chiral molecules have 1 or more chiral carbon atoms
(each of which is bonded to 4 different groups)
Lines are in plane of paper
H
H3C
Cl
Br
Wedges point out at us
Dashes point away from us
4
Identify the Chiral Carbons
Lipitor (atorvastatin)
HO
O
OOH
F
N
Ca2+
O
HN
2
5
Answer
Two
HO
O
*
OOH
*
F
N
Ca2+
O
HN
2
6
Mirror Images
• Mirror images of chiral compounds cannot be
superimposed.
•
pairs of stereoisomers are called enantiomers
• Example: When the H & I atoms are aligned,
the Cl & Br atoms are on opposite sides.
7
Achiral Structures are Superimposable
Rotation of the mirror image of an achiral
structure can be aligned with the initial
structure → superimposable
8
Chirality: Who Cares?
Tremendously important in all aspects of chemistry,
including biochemistry!!!
Most biological molecules are chiral (DNA, proteins,
etc.)
Different enantiomers often elicit diff. responses
Big $ in chemical industry for producing chiral drugs
9
Chirality: Who Cares?
Enzymes, industrial catalysts, etc. are often
tailored to recognize a particular enantiomer and
produce chiral species
10
Fischer Projections
• are a 2-dimensional representation of a 3-D
molecule.
• places the most oxidized group at the top.
• uses vertical lines in place of dashes for
bonds that go back.
• uses horizontal lines in place of wedges for
bonds that come forward.
11
Drawing Fischer Projections
12
D and L Notations
• By convention, the letter L is assigned to the
structure with the —OH on the left.
• The letter D is assigned to the structure with the
—OH on the right.
• FYI: Other conventions exist too…
13
Learning Check
Indicate whether each pair is a mirror image
that cannot be superimposed (enantiomers).
CH2OH
A.
B.
H
H
C
CH3
CH2OH
and
CH3 C
Br
Br
Cl
Cl
C
H
CH3
and
CH3 C
H
Yes
H
No
H
14
Carboxylic Acids (13.1)
15
Carboxylic Acids
A carboxylic acid contains a carboxyl group, which
• is a carbonyl group (C=O) attached to a hydroxyl
group (—OH).
• is found on carbon 1 in carboxylic acids.
O

CH3 — C—OH
hydroxyl group
carbonyl group
Will also see a carboxylic acid written as CH3COOH
16
Models of Carboxylic Acids
The 3D models show the geometry of atoms
in carboxylic acid molecules.
17
Recognizing Carboxylic Acids from Names
The IUPAC names of carboxylic acids:
• Replace the -e in the alkane name with -oic acid.
CH4
methane HCOOH
CH3—CH3 ethane
methanoic acid
CH3—COOH ethanoic acid
• Number substituents from the carboxyl carbon 1.
CH3
O
|
║
Don’t need to
CH3—CH—CH2—C—OH
know numbering
4
3
2
1
rules!!!
3-methylbutanoic acid
18
Names & Sources of Some Carboxylic Acids
(Know These)
By the way, very common in nature:
Citric acid, tartaric acid, lactic acid, fatty acids, etc.
19
Polarity of Carboxylic Acids
• strongly polar because they have two polar groups:
[hydroxyl (−OH) and carbonyl (C=O)]
• form dimers in which hydrogen bonds form
between two carboxyl groups.
O … H—O
||
|
CH3—C
C—CH3
|
||
O—H … O
A dimer of acetic acid
• have higher boiling points than alcohols, ketones,
and aldehydes of similar mass.
20
Comparison of Boiling Points
Compound
O
║
CH3−CH2−C−H
Molar Mass
Boiling Point
58
49°C
CH3−CH2−CH2−OH
60
97°C
O
║
CH3−C−OH
60
118°C
21
Solubility in Water
Carboxylic acids:
• form hydrogen
bonds with many
water molecules.
Water molecules
• with 1-4 carbon
atoms are very
soluble in water.
22
Boiling Points and Solubility
23
Acidity of Carboxylic Acids
Carboxylic acids
• are weak acids.
• ionize in water to produce carboxylate
ions and hydronium ions.
O
║
CH3−C−OH + H2O
O
║
CH3−C−O– + H3O+
24
Neutralization of Carboxylic Acids
Carboxylic acid salts
• are a product of the neutralization of a carboxylic acid
with a strong base.
CH3—COOH + NaOH
CH3—COO– Na+ + H2O
acetic acid
sodium acetate
(carboxylic acid salt)
• are used as preservatives and flavor enhancers.
25
Learning Check
Write the equation for the reaction of propanoic acid with
A. water
CH3—CH2—COOH + H2O
CH3—CH2—COO– + H3O+
B. KOH
CH3—CH2—COOH + KOH
CH3—CH2—COO – K+ + H2O
26
Esters
In an ester, the H in the carboxyl group is replaced
with an alkyl group.
O

CH3 — C—O —CH3
ester group
27
Esterification
Esterification: reaction of a carboxylic acid &
alcohol in the presence of an acid catalyst to
produce an ester.
O

CH3—C—OH + H—O—CH2—CH3
H+
O

CH3—C—O—CH2—CH3 + H2O
ethyl acetate (an ester)
FYI: The acid half of an ester is called an “acyl” group
28