15-1Chemistry 121, Winter 2011, LA Tech
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: [email protected]
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(01) Winter 2010-11
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Chapter 15: Aldehyde and Ketones15.1 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
15-3Chemistry 121, Winter 2011, LA Tech
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
C
O
OH
Carboxylic AcidFunctional Group
C
O
O
EsterFunctional Group
C
O
NH
AmideFunctional Group
Aldehydes and Ketones
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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
Aldehyde Functional Group
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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
Propanone(Acetone)
Ethanal(Acetaldehyde)
Methanal(Formaldehyde)
O O O
CH3CHHCH CH3CCH3
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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 chemistry
C O
CarbonylPolarity of Carbonyl Group
C
O120o120o
120o
Geometry of Carbonyl Group
Carbonyl group:
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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.
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IUPAC RulesRule 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.
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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
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Common NamesAldehydes: Fomaldehyde: HCHO
Acetaldehyde: CH3CHO
Propionaldehyde: CH3CH2CHO
Butyraldehyde: CH3CH2CH2CHO
Valeraldehyde: CH3CH2CH2CH2CHO Ketones:
Acetone: CH3COCH3
Methyl ethyl ketone CH3CH2COCH3 Butyl propyl ketone
CH3CH2CH2CH2COCH2CH2CH3
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Nomenclature
CHO HO CHO
Cyclopentane-carbaldehyde
trans-4-Hydroxycyclo-hexanecarbaldehyde
14
3-Methylbutanal 2-Propenal(Acrolein)
H
O
(2E)-3,7-Dimethyl-2,6-octadienal(Geranial)
1
2
3
4
5
6
7
8
11
223
3
4H
O
H
O
2-Methyl-cyclohexanone
5-Methyl-3-hexanone
Benzophenone Acetophenone
OO
O O
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Nomenclature
HCOOH
O
COOHO
COOHHO
OHHS
COOHNH2
-al oxo-
Ketone -one oxo-
Alcohol -ol hydroxy-
Amino -amine amino-
3-Oxopropanoic acid
3-Oxobutanoic acid
4-Hydroxybutanoic acid
3-Aminobutanoic acid
Example of When the FunctionalGroup Has a Lower Priority
Sulfhydryl -thiol mercapto- 2-Mercaptoethanol
Functional Group Suffix Prefix
Carboxyl -oic acid
Aldehyde
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Name the Aldehyde
2,4-dimethylpentanal
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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
Butanal
O
2-Methylpropanal
O
2-Pentanone
O
3-Pentanone
Skeletal isomersPositional isomers
Constitutional isomers of aldehydes and ketones
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Examples of Aldehyde and KetonesFormaldehyde
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
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Examples of Aldehyde and KetonesAcetone 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.
15-17Chemistry 121, Winter 2011, LA Tech
Important AldehydesMethanal 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:
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Naturally Occurring Aldehydes and KetonesAldehydes 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.
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Physical properties of aldehydes and ketones.
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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
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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.
C
O C
O
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SolubilityWater 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.
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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
Preparation of Aldehydes and Ketones
15-24Chemistry 121, Winter 2011, LA Tech
Oxidation of Aldehydes and Ketones:• Aldehydes readily undergo oxidation to
carboxylic acids• Ketones are resistant to oxidation
Reactions of Aldehydes and Ketones
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Preapration of Aldehydes:
Partial oxidation of primary alcohols with H2CrO4:
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Oxidation of alcohol
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Preapration of ketones:
Oxidation of secondary alcohols with KMnO4, or H2CrO4
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Oxidation of alcohol
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Chemical Reactions
Oxidation of aldehyde.
Benedict's Test for aldehydes:
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Test for Urine Glucose: Benedict’s Test
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Oxidation of aldehyde.
The commercial manufacture of silver mirrors uses a similar process.
Tollen's Test:
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Reduction of als & ones compounds to alcohols:
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Addition reactions of als & onesHemiacetal or hemiketal formation
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Hemiacetal form of cyclic sugars
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Formation of Acetals and Ketals.
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Addition of HCN and H2O
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Aldol Condensation
In biological systems this reaction is catalysed by an enzyme named aldolase.
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Keto & Enol tautomers
keto form enol from
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Keto & Enol tautomers in sugars
aldehyde enol ketone
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Tollens test: Test for AldehydeTollens 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.
R C
O
H + Ag+NH3, H2O, Heat
R C
O
OH + Ag
15-41Chemistry 121, Winter 2011, LA Tech
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)
R C
O
H + Cu2+R C
O
OH + Cu2O
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Reduction of Aldehydes and KetonesAldehydes 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.
R C
O
HNi
R C
O
R
R C
OH
H
H
R C
OH
R
H
+ H2
+ H2Ni
Primary Alcohol
Secondary Alcohol
15-43Chemistry 121, Winter 2011, LA Tech
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
Formation of Hemiacetals and Acetals
15-44Chemistry 121, Winter 2011, LA Tech
Simplest Aldehyde
15-45Chemistry 121, Winter 2011, LA Tech
Practice Exercise
Answers:
a. Yes
b. Yes
c. No
d. Yes
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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.
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Bakelite
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Formaldehyde is a prolific “polymer former”
Under acidic conditions, reaction between formaldehyde and phenol forms a phenol–formaldehyde network polymer
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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
Thioaldehydes (thials) and Thioketones