1 nucleophilic reactions of carbonyl groups oxygen is more electronegative than carbon (3.5 vs 2.5)...
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Nucleophilic reactions of carbonyl groups
•Oxygen is more electronegative than carbon (3.5 vs 2.5) and, therefore, a C=O group is polar
C O C O –
Polarity of acarbonyl group
-+C O
+
More importantcontributing
structure
::: : :
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Under basic conditions -> Nucleophilic addition
Under acidic conditions -> Electrophilic addition
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– 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
– aldehydes and ketones are polar compounds and interact in the pure state by dipole-dipole interactions
– they have higher boiling points and are more soluble in water than nonpolar compounds of comparable molecular weight
Propanone(Acetone)
Ethanal(Acetaldehyde)
Methanal(Formaldehyde)
O O O
CH3CHHCH CH3CCH3
Nucleophilic reactions of Ketones and Aldehydes
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Nomenclature
• IUPAC names:– the parent chain is the longest chain that contains the
carbonyl group– for an aldehyde, change the suffix from -e-e to -al-al– for a cyclic molecule in which -CHO is bonded to the
ring, add the suffix –carbaldehydecarbaldehyde– For a For a ketoneketone, change the suffix from , change the suffix from –e –e toto –one –one– for an unsaturated aldehyde or ketone, show the
carbon-carbon double bond by changing the infix from --an-an- to -en--en-; the location of the suffix determines the numbering pattern
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Nomenclature
CHO HO CHO
Cyclopentane-carbaldehyde
trans-4-Hydroxycyclo-hexanecarbaldehyde
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3-Methylbutanal 2-Propenal(Acrolein)
H
O
(2E)-3,7-Dimethyl-2,6-octadienal(Geranial)
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2
3
4
5
6
7
8
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223
3
4H
O
H
O
2-Methyl-cyclohexanone
5-Methyl-3-hexanone
Benzophenone Acetophenone
OO
O O
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Nomenclature
• Common names– for an aldehyde, the common name is derived from the
common name of the corresponding carboxylic acid– for a ketone, name the two alkyl or aryl groups bonded
to the carbonyl carbon and add the word ketone
FormaldehydeFormic acid Acetaldehyde Acetic acid
Ethyl isopropyl ketoneDiethyl ketoneDicyclohexyl ketone
O OO
H H
O
H OH
O
H
O
OH
O
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Nucleophilic reactions of Ketones and Aldehydes
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Nucleophilic reactions of Ketones and Aldehydes – Nucleophile as leaving
group For base-catalysed reaction:
For acid-catalysed reaction:
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Addition of 1 mol of Alcohol to Aldehyde -> Hemiacetal
Addition of 1 mol of Alcohol to Keton -> Hemiketal
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Sugars form stable hemiacetals or hemiketals in solution
Anomeric center/carbon
Mixture of α and β is NOT racemat -> Mixture of diastereoisomers (since there are other chiral centers in the molecule)
Glucose can form 5- and 6-ring hemiacetals.
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Mutarotation -> in solution
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Ribose can form 5- and 6-ring hemiacetals
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Ribose can form 5- and 6-ring hemiacetals
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Biological important hemiacetals -> sugars Ribonucleic Acids -> RNA
Deoxyribonucleic Acids -> DNA
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Biological important hemiacetals -> sugars Coenzyme A -> transfers acetyl
ATP -> high energy transfer compound
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Addition of 2 mol of Alcohol to Aldehyde -> Acetal
Addition of 2 mol of Alcohol to Keton -> Ketal
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Acetal and ketal linkages are found in sugars and polysaccharides
-> Formation of sucrose
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Nucleophilic reactions of Ketones and Aldehydes – Oxygen as a nucleophile
Acetal and ketal linkages are found in sugars and polysaccharides
-> Formation of Polysaccharides
Starch: Amylase + Amylopectine
Cellulose: acetal linkage β1->4
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Nucleophilic reactions of Ketones and Aldehydes – Hydride as a nucleophile
Reduction of aldehydes and ketons
Complex metal hydrides (LiAlH4 or NaBH4) can deliver hydride -> they act like
nucleophiles
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Nucleophilic reactions of Ketones and Aldehydes – Hydride as a nucleophile
Reduction of aldehydes and ketons
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Nucleophilic reactions of Ketones and Aldehydes – Hydride as a nucleophile
Reduction of aldehydes and ketons
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Nucleophilic reactions of Ketones and Aldehydes – Hydride as a nucleophile
Reduction of aldehydes and ketons
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Nucleophilic reactions of Ketones and Aldehydes – Carbon as a nucleophile
Cyanide -> Cyanohydrin
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Nucleophilic reactions of Ketones and Aldehydes – Carbon as a nucleophile
Cyanide -> also toxic compounds in plants (laurel, bitter almonds)
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Nucleophilic reactions of Ketones and Aldehydes – Carbon as a nucleophile
Organometallics: Grignard reagents
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Addition of primary amine to carbonyl -> Imine (Schiff base)
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Addition of primary amine to carbonyl -> Imine (Schiff base)
Equilibrium
Stronger acid -> deprotonates -> Imine
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Imine (Schiff base) are nitrogen analogues of carbonyl groups
=>
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Imine (Schiff base) are nitrogen analogues of carbonyl groups
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Imine (Schiff base) are nitrogen analogues of carbonyl groups
-> Nitriles are also carbonyl-like compounds
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Nucleophilic reactions of Ketones and Aldehydes – Nitrogen as a nucleophile
Imine (Schiff base) are nitrogen analogues of carbonyl groups
-> Nitriles are also carbonyl-like compounds