Chemistry 121(01) Winter 2010-11
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: upali@chem.latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MWF 8:00 am - 10:00 am;
TT 9:00 – 10:00 am & 1:00-2:00 pm.
December 17, 2010 Test 1 (Chapters 12-13)
January 19, 2011 Test 2 (Chapters 14,15 & 16)
February 7, 2011 Test 3(Chapters 17, 18 & 19)
February 23, 2011 Test 4 (Chapters 20, 21 & 22)
February 24, 2011
Comprehensive Make Up Exam:
Chemistry 121, Winter 2011, LA Tech
15-1
Chapter 15: Aldehyde and Ketones
15.1 The Carbonyl Group
15.2 Compounds Containing a Carbonyl Group
15.3 The Aldehyde and Ketone Funcitonal Groups
15.4 Nomenclature for Aldehydes
15.5 Nomenclature for Ketones
15.6 Isomerism for Aldehydes and Ketones
15.7 Selected Common Aldehydes and Ketones
15.8 Physical Properties of Aldehydes and Ketones
15.9 Preparation of Aldehydes and Ketones
15.10 Oxidation and Reduction of Aldehydes and Ketones
15.11 Reaction of Aldehydes and Ketones with Alcohols
15.12 Formaldehyde-Based Polymers
15.13 Sulfur-Containing Carbonyl Groups
Chemistry 121, Winter 2011, LA Tech
15-2
Aldehydes and Ketones
Aldehydes: Carbonyl is attached to at least one H atom
in aldehydes
Ketones: Carbonyl is directly attached with two carbon
atoms in ketones
Carboxylic acids: carbonyl carbon atom bonded to a
hydroxyl group.
Esters: carbonyl carbon atom bonded to an oxygen
atom
Amide: carbonyl carbon atom bonded to a nitrogen
atom
O
O
C
Chemistry 121, Winter 2011, LA Tech
OH
Carboxylic Acid
Functional Group
C
O
O
Ester
Functional Group
C
NH
Amide
Functional Group
15-3
Aldehyde Functional Group
Aldehyde functional group: –CHO
Ketone functional group: carbonyl carbon (C=O)
attached to carbon atoms
Cyclic aldehydes are not possible but cyclic
ketones are known
Cyclic ketones are not heterocyclic ring
systems
Chemistry 121, Winter 2011, LA Tech
15-4
Structure
• the functional group of an aldehyde is a carbonyl group
bonded to a H atom
• the functional group of a ketone is a carbonyl group
bonded to two carbon atoms
O
HCH
Methanal
(Formaldehyde)
Chemistry 121, Winter 2011, LA Tech
O
CH 3 CH
Ethanal
(Acetaldehyde)
O
CH 3 CCH 3
Propanone
(Acetone)
15-5
Carbonyl group:
Carbonyl group: A carbon atom double-bonded to an
oxygen atom
Aldehydes and ketones are the compounds which
contain a carbonyl functional group
C=O bond is polar (oxygen gets partial negative and
carbon gets partial positive charge) C=C is non polar
All carbonyl groups have a trigonal planar structure
Compounds with C=O and C=C both exhibit different
O
chemistry
o
120o
C
120
C O
120o
Carbonyl
Chemistry 121, Winter 2011, LA Tech
Geometry of
Carbonyl Group
Polarity of Carbonyl Group
15-6
IUPAC Nomenclature of Aldehyde and
Ketones
The IUPAC system deals with functional
groups two different ways.
Modification of the hydrocarbon name to
indicate the presence of a functional group.
aldehyde, -CHO
use -al ending.
Ketones -RCOR’
use -one ending.
Chemistry 121, Winter 2011, LA Tech
15-7
IUPAC Rules
Rule 1: Select as the parent carbon chain the longest carbon
chain that includes the carbon atom of the carbonyl group.
Rule 2: Name the parent chain by changing the “-e” ending of
the corresponding alkane name to “-one.”
Rule 3: Number the carbon chain such that the carbonyl
carbon atom receives the lowest possible number. The
position of the carbonyl carbon atom is noted by placing a
number immediately before the name of the parent chain.
Rule 4: Determine the identity and location of any
substituents, and append this information to the front of the
parent chain name.
Rule 5: Cyclic ketones are named by assigning the number 1
to the carbon atom of the carbonyl group. The ring is then
numbered to give the lowest number(s) to the atom(s)
bearing substituents.
Chemistry 121, Winter 2011, LA Tech
15-8
Example
C - C - C - C - CHO
Base contains 5 carbon
- aldehyde name is pentane
- remove -e and add -al
C - C - C - C - CO-C-C
Base contains 7 carbon
- aldehyde name is heptane
- remove -e and add -one
3-heptanone
Chemistry 121, Winter 2011, LA Tech
15-9
Common Names
Aldehydes:
Fomaldehyde:
HCHO
Acetaldehyde:
CH3CHO
Propionaldehyde:
CH3CH2CHO
Butyraldehyde:
CH3CH2CH2CHO
Valeraldehyde:
CH3CH2CH2CH2CHO
Ketones:
Acetone:
CH3COCH3
Methyl ethyl ketone
CH3CH2COCH3
Butyl propyl ketone
CH3CH2CH2CH2COCH2CH2CH3
Chemistry 121, Winter 2011, LA Tech
15-10
Nomenclature
O
O
3
4
2
3
H
3-Methylbutan al
CHO
H
2
2-Propen al
(A crolein )
HO
Cyclopen tanecarb aldehyde
4
1
5
7
8
6
3
4
1
2
H
(2E)-3,7-D imeth yl-2,6-octad ienal
(Geran ial)
CHO
trans -4-Hyd roxycyclohexan ecarbald ehyde
O
O
5-Methyl-3h exanone
O
1
1
2-Methylcycloh exanone
Chemistry 121, Winter 2011, LA Tech
O
Acetop hen on e
O
Benzoph enone
15-11
Nomenclature
Functional
Grou p
Su ffix
Carb oxyl
-oic acid
Ald ehyde
-al
Prefix
Example of When the Fun ction al
Grou p Has a Low er Priority
O
oxo-
3-Oxopropan oic acid
COOH
H
O
COOH
Ketone
-one
oxo-
3-Oxobutanoic acid
Alcoh ol
-ol
hydroxy-
4-Hydroxybutan oic acid HO
COOH
NH2
Amino
-amine
Su lfh ydryl -thiol
Chemistry 121, Winter 2011, LA Tech
amino-
COOH
3-Aminobutan oic acid
mercapto- 2-Mercaptoethanol
HS
OH
15-12
Name the Aldehyde
2,4-dimethylpentanal
Chemistry 121, Winter 2011, LA Tech
15-13
Constitutional isomers of
aldehydes and ketones
Constitutional isomers exist for aldehydes and ketones
Isomers between aldehydes and ketones are called
functional group isomers
Two types of isomers:
• Skeletal isomers: arrangements of atoms in space
is different.
• Positional isomers: Position of the functional group
is different.
O
O
O
O
Butanal
2-Methylpropanal
Skeletal isomers
Chemistry 121, Winter 2011, LA Tech
2-Pentanone
3-Pentanone
Positional isomers
15-14
Examples of Aldehyde and Ketones
Formaldehyde
Simplest aldehyde and has one carbon atom
It is synthesized by oxidation of methanol
Mainly used for the manufacturing of polymers
Bubbling formaldehyde through water produces
formalin (formaldehyde in water with pungent
smell)
Formalin is used for preserving biological
specimens
In formalin formaldehyde is present in the form of
HO-CH2-OH
Chemistry 121, Winter 2011, LA Tech
15-15
Examples of Aldehyde and Ketones
Acetone is the simplest ketone.
Colorless liquid with mild sweet odor.
Excellent solvent: it is miscible in both water and organic
solvents.
Acetone is the main ingredient in gasoline treatments
designed to solubilize water in the gas tank and allow it to
pass through the engine in miscible form.
Major component of nail polish remover.
Patients with diabetes produce large amounts of acetone.
• Diabetic breath has mild sweet odor because of
acetone.
• Presence of acetone in urine indicates diabetes.
Chemistry 121, Winter 2011, LA Tech
15-16
Important Aldehydes
Methanal or formaldehyde
Ethanal or acetaldehyde
2-Propanone or acetone
2-Butanone or methyl ethyl ketone
Oil of almonds or benzaldehyde
Oil of Cinnamon or cinnamaldehyde
Oil of vanilla beans or vanillin
Mushroom flavoring or 2-octanone
Oil of lemongrass or citral:
Chemistry 121, Winter 2011, LA Tech
15-17
Naturally Occurring Aldehydes and
Ketones
Aldehydes and ketones occur widely in nature
Such compounds have higher molecular masses,
pleasant odors and flavors
Often used in consumer products such as
perfumes, air fresheners, etc).
Example: Butanedione
The unmistakable odor of melted butter is largely
due to the four-carbon diketone - butanedione.
Chemistry 121, Winter 2011, LA Tech
15-18
Physical properties of aldehydes and
ketones.
Chemistry 121, Winter 2011, LA Tech
15-19
Physical State at Room Temperature
Aldehydes:
• C1-C2 aldehydes are gases
• C3-C11 straight-chain aldehydes are liquids
• >C11 aldehydes are solids
Ketones:
• Lower molar mass ketones are colorless
liquids
Chemistry 121, Winter 2011, LA Tech
15-20
Boiling and Melting Points
Intermediate between alcohols and alkanes
Higher boiling points than alkanes because of
dipole–dipole attractions between carbonyl
groups in these molecules.
Chemistry 121, Winter 2011, LA Tech
O 
C


C
 O
15-21
Solubility
Water molecules can hydrogen-bond with
aldehyde and ketone molecules, which
causes low-molecular-mass aldehydes and
ketones to be water soluble.
Aldehydes and ketones with longer
hydrocarbon chains are less soluble or
insoluble in water.
Chemistry 121, Winter 2011, LA Tech
15-22
Preparation of Aldehydes and Ketones
Oxidation of Alcohols
Aldehydes produced by the mild oxidation of
primary alcohols
Ketones are produced by the mild oxidation of
secondary alcohols
Oxidizing agents(mild): KMnO4 or K2Cr2O7
Chemistry 121, Winter 2011, LA Tech
15-23
Reactions of Aldehydes and Ketones
Oxidation of Aldehydes and Ketones:
• Aldehydes readily undergo oxidation to
carboxylic acids
• Ketones are resistant to oxidation
Chemistry 121, Winter 2011, LA Tech
15-24
Preapration of Aldehydes:
Partial oxidation of primary alcohols with H2CrO4:
Chemistry 121, Winter 2011, LA Tech
15-25
Oxidation of alcohol
Chemistry 121, Winter 2011, LA Tech
15-26
Preapration of ketones:
Oxidation of secondary alcohols with KMnO4, or
H2CrO4
Chemistry 121, Winter 2011, LA Tech
15-27
Oxidation of alcohol
Chemistry 121, Winter 2011, LA Tech
15-28
Chemical Reactions
Oxidation of aldehyde.
Benedict's Test for aldehydes:
Chemistry 121, Winter 2011, LA Tech
15-29
Test for Urine Glucose: Benedict’s Test
Chemistry 121, Winter 2011, LA Tech
15-30
Tollen's Test:
Oxidation of aldehyde.
The commercial manufacture of silver
mirrors uses a similar process.
Chemistry 121, Winter 2011, LA Tech
15-31
Reduction of als & ones compounds
to alcohols:
Chemistry 121, Winter 2011, LA Tech
15-32
Addition reactions of als & ones
Hemiacetal or hemiketal formation
Chemistry 121, Winter 2011, LA Tech
15-33
Hemiacetal form of cyclic sugars
Chemistry 121, Winter 2011, LA Tech
15-34
Formation of Acetals and Ketals.
Chemistry 121, Winter 2011, LA Tech
15-35
Addition of HCN and H2O
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15-36
Aldol Condensation
In biological systems this reaction is
catalysed by an enzyme named aldolase.
Chemistry 121, Winter 2011, LA Tech
15-37
Keto & Enol tautomers
keto form
Chemistry 121, Winter 2011, LA Tech
enol from
15-38
Keto & Enol tautomers in sugars
aldehyde
Chemistry 121, Winter 2011, LA Tech
enol
ketone
15-39
Tollens test: Test for Aldehyde
Tollens test (silver mirror test): Tollens reagent
[aqueous silver nitrate (AgNO3) and ammonia (NH3)]
when added to an aldehyde, Ag+ ion is reduced to
silver metal, which deposits on the inside of the test
tube, forming a silver mirror.
• The appearance of this silver mirror is a positive
test for the presence of the aldehyde group.
• The Ag ion will not oxidize ketones.
O
R
C H
O
+ Ag+
Chemistry 121, Winter 2011, LA Tech
NH3 , H2 O, Heat
R
C OH + Ag
15-40
Benedict’s Test: Test for Aldehyde
Similar to the Tollens test except that the metal ion
oxidizing agent is Cu2+
Cu 2+ ion is reduced to Cu ion, which precipitates from
solution as Cu2O (brick-red colored solid)
O
R
C H
O
+ Cu2+
Chemistry 121, Winter 2011, LA Tech
R
C OH + Cu2O
15-41
Reduction of Aldehydes and Ketones
Aldehydes and ketones are easily reduced by
hydrogen gas (H2), in the presence of a
catalyst (Ni, Pt, or Cu), to form alcohols.
• Aldehydes produces primary alcohols.
• Ketones yield secondary alcohols.
OH
O
R
C
H + H2
R
Ni
C
H
H
Primary Alcohol
O
R
C
OH
R + H2
Ni
R
C
R
H
Chemistry 121, Winter 2011, LA Tech
Secondary Alcohol
15-42
Formation of Hemiacetals and Acetals
Aldehydes and ketones react with alcohols to
form hemiacetals and acetals.
Hemiacetal formation: A hemiacetal is an
organic compound in which a carbon atom is
bonded to both a hydroxyl group (—OH) and
an alkoxy group (—OR).
A hemiacetal can also be formed due to the
reaction between an —OH and C=O
functional groups with in the same molecule.
Such a reaction produces a cyclic hemiacetal
Cyclic hemiacetals are more stable
Chemistry 121, Winter 2011, LA Tech
15-43
Simplest Aldehyde
Chemistry 121, Winter 2011, LA Tech
15-44
Practice Exercise
Answers:
a. Yes
b. Yes
c. No
d. Yes
Chemistry 121, Winter 2011, LA Tech
15-45
Acetal Formation and Hydrolysis
Acetal Formation: An acetal is an organic
compound in which a carbon atom is bonded
to two alkoxy groups (—OR).
Acetal Hydrolysis: Undergo hydrolysis in
acidic solution to form the aldehyde or
ketone and alcohols that originally reacted to
form the acetal.
Chemistry 121, Winter 2011, LA Tech
15-46
Bakelite
Chemistry 121, Winter 2011, LA Tech
15-47
Formaldehyde is a prolific “polymer former”
Under acidic conditions, reaction between
formaldehyde and phenol forms a phenol–
formaldehyde network polymer
Chemistry 121, Winter 2011, LA Tech
15-48
Thioaldehydes (thials) and Thioketones
Replacement of carbonyl oxygen with sulfur produces
thioaldehydes (thials) and thioketones (thiones)
• These are unstable and readily decompose.
Replacement of the carbonyl carbon atom with sulfur
produces sulfoxides.
• Sulfoxides are much more stable than thiocarbonyls
• Most important example: DMSO (dimethyl sulfoxide)
• DMSO is an odorless liquid with excellent solvent
properties
• DMSO is quickly absorbed into the body and is known
to relieve pain and inflammation
• Not approved by the FDA for medical uses because of
possible side effects
Chemistry 121, Winter 2011, LA Tech
15-49