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Principles and Applications ofInorganic, Organic, and Biological

ChemistryDenniston, Topping, and Caret

4th ed

Chapter 14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Power Point to Accompany

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Carbonyl Compounds

Contain the carbonyl group, C=O

Shortforms

Aldehydes: R may be hydrogen usually a carbon containing group

R C

O

R

R C

O

H RCHO

Ketones: R contains carbon R C

O

R RCOR

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14.1 Structure and Physical Properties

The carbonyl group is polar. The oxygen end is negative. C

O

+

-

C

O H OH

Hydrogenbond

Carbonyls of less than six carbons are at least partly water soluble. They can H bond to water.

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Boiling PointsCarbonyl compounds boil between alkanes

and alcohols of similar molecular weight.

butane, bp -43o propanal, bp 50o

propanone, bp 56o propanol, bp 97o

CH3CH2CH2CH3 CH3CH2CH

O

CH3C CH3

O

CH3CH2CH2OH

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14.2 Nomenclature

AldehydesCommon: H2C=O formaldehyde (a gas)

Used to make insulation and plastic dinnerware.

Also using traditional names and Greek letter substitution patterns. E. g.

CH2CH2CH

O

CHCH3

Cl

-chlorovaleraldehyde

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Naming Aldehydes: IUPAC NamesBase name: longest chain with the C=OReplace the -e of alkane name with -al

CH3CH CH2CH2CHO

CH34-methylpentanal

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Naming Ketones

Common: acetone, an important solvent

CH3 C CH3

O

Also by naming the two alkyl groups attached to the carbonyl in a) alphabetical order or b) by increasing size

CH3C CH2

OCH3

Methyl ethyl ketone orEthyl methyl ketone

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Naming Ketones: IUPACBase name: longest chain with the C=O

Replace the -e of alkane name with -one

Indicate position of C=O by number on chain

4-chloro-2-pentanone

CH3CH CH2C CH3

OCl

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14.3 Carbonyl ExamplesMethanal (b.p. –21 oC) is used in aqueous

solutions as formalin to preserve tissue and embalm.

Acetone and methyl ethyl ketone (MEK) are very versatile solvents.

Other examples:

CH3 CH2 C

O

CH35OH CO

HCH3O

VanillinVanilla beans

2-octanoneMushroom flavor

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14.4 Reactions of CarbonylsAldehydes are prepared from primary

alcohols by oxidation with a mild oxidizer, eg (CrO3/py), pyridinium dichromate

Example: Note: this oxidation removes two hydrogens. It is also an oxidative elimination reaction.

CH3CH2CH

O

CH3CH2CH2OHCrO3

in py or

H2CrO4

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Preparation of Ketones

Prepared from 2o alcohols

by oxidation with Cr(VI) or Mn(VII) species

The oxidation removes two hydrogens and forms a double bond. It is also an elimination reaction!

OH OKMnO4 orK2Cr2O7 or CrO3,py

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Reactions of Carbonyls1. Redox

a) Aldehydes: oxidized to carboxylic acidsb) Aldehydes and ketones are reduced to

alcohols: aldehydes to primary alcohols and ketones to secondary alcohols

2. Additiona) of hydrogen to give alcoholsb) of alcohols to give hemiacetals, acetals,

hemiketals, and ketalsc) of aldehydes/ketones to give aldol (-

hydroxy carbonyl) products

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Oxidation of AldehydesAldehydes are easily oxidized to

carboxylic acids by almost any oxidizing agent.

Visual tests for the aldehyde functional group based on its easy oxidation are:

Tollen’s TestSilver ion is the oxidizer, as Ag(NH3)2

+

Benedict’s TestCu2+ in a basic solution is the oxidizer.

Solution is a distinctive blue color. Color fades with rxn.

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Oxidation of Aldehydes-2

Tollen’s test uses silver ion and gives a silver mirror on the glass reaction container

As mirroron test tube

CH3CH2CHO

CH3CH2CO

OAg(NH3)2

+

+ Ag

CH3CHO

CH3CO

OKMnO4

H2O, OH-

CHO

CO

OHH2CrO4

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Oxidation of Aldehydes-3

Fehling’s test uses copper ion. The blue color fades giving a red ppt of Cu2O. (Often used to test for simple reducing sugars.)

CCH2OH

OHHC OHHCOH H

CC

O H

OHH

CCH2OH

OHHC OHHCOH H

CC

O O

OHH2 Cu2+

OH-

+ Cu2O

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Reduction of Carbonyls

Reduction occurs with hydrogen.

The reaction is also an addition reaction.

CH3CH2C CH3

O

CH3CH2CH2CHO

CH3CH2CHCH3

OH

CH3CH2CH2CH2

OH

H2 Pt, Pd, Ni

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Additions to Carbonyls: Alcohols

Carbonyls add one molecule of alcohol to give usually unstable hemiacetals and hemiketals

Hemiacetal(ketal) carbons are part of both alcohol and ether functions and are a new functional group

CH3CH2CH2CHO

CH3OH CH3CH2CH2CHOH

O CH3

CH3CH2CO

CH3 CH3CH2COH

O CH3

CH3CH3OH

+H+

+H+

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Additions to Carbonyls: Alcohols-2

Acid catalyzes both aldehydes and ketones to react with two molecules of alcohol to give acetals and ketals

Acetal(ketal) carbons are part of twoether groups and are a newfunctional group

CH3CH2CHO

CH3OH

CH3CH2CO

CH3 CH3OH

CH3CH2CHO CH3

O CH3

CH3CH2CO

CH3

CH3

O CH3

+

+ 2

2 H+

H+

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Additions to Carbonyls: Alcohols-3

Glucose forms a cyclic hemiacetal when the alcohol group on C-5 reacts with the aldehyde group C=O.

CH2OHO

CH

OH

OH

OH

OH

CH2OHO

CO

HOH

OH

OH

H

hemiacetal carbon

hemiacetal link forms here

this H is involvedin hemiacetal formation

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Hydrolysis of (Hemi)acetals/ketalsBoth hemiacetals and acetals (and ketone

analogs) hydrolyze (react with water). An acid catalyst takes them back to the carbonyl compound and the alcohol(s).

acetal

hemiketal

CH3CH2CO

CH3CH3OH

CH3CH2CO

CH3

H

O CH3+

H+

H+

CH3CH2CHO CH3

O CH3

H2O+ CH3CH2CHO

CH3OH+2

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Keto-enol TautomersTautomers are isomers which differ in the

placement of an atom of hydrogen and a double bond. The keto form has a C=O while the enol form has a C=C.

The keto form is usually the most stable.

R1 CR2

HCO

R3

C CHH

OHHH C

H

HCO

H

C C

R1

R2

OH

R3

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Additions to Carbonyls: Aldol CondensationSelf Addition or Condensation

Uses two molecules of the same aldehyde or ketone.

The alpha carbon of the second molecule adds to the carbonyl carbon of the first molecule.

Strong base such as hydroxide catalyzes the reaction.

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Aldol Condensation-2Self Addition/Condensation: aldehyde

alpha carbon,second molecule

carbonyl carbon of first molecule becomes alcohol carbon in aldol

originalalphacarbon

An aldol has an OH beta to the carbonyl group

CH3CH

O

CH3CH

OH

CH2CH

OOH-CH3CH

O

+

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Aldol Condensation: AldolaseDihydroxyacetone phosphate + D-glyeraldehyde-3-phosphate

D-fructose-1,6-bisphosphate

Alpha carbon (3) adds to carbonyl carbon (4). (Gluconeogenesis)

Bond formed

CH2 OPO32-

CC OH

O

HH

CH OCHCH2 OPO3

2-OH

1

2

3

4

5

6

CH2 OPO32-

CC OH

OH

CH OCHCH2 OPO3

2-OH

H

1

2

3

4

5

6

aldolase

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Carbonyl Compounds

The End