This group of organic compounds containing two functional groups, the carbonyl group and carbon-carbon double bond.In other word we can consider imagery that is including the conjugated diene skeleton as follows.

--Unsaturated Carbonyl Compound

O

R R'

We choose the longest carbon skeleton containing the double bond and the carbonyl group and numbering it whereas the carbon of carbonyl group take the No. 1 in aldehydes, and both the carbonyl group and unsaturated bond the lowest numbers in case of ketones.Then giving the name of aldehyde or ketone as you study in aldehydes and ketones in the first year with designating the position of double bond.

Nomenclature:

O

CH3 CH31

23

4

Pent-3-en-2-one

O

CH3 H

1234

2-Butenal or But-2-enal

5

O

CH3 CH3

CH3 12

3

45

Hex-3-en-2-one

6 O

H3C H

H3C

3-Methyl-but-2-enal

12

34

In the -unsaturated carbonyl compounds, the carbon-carbon double bond and the carbon-oxygen double bond are separated by just one carbon-carbon single bond; that is, the double bonds are conjugated. Because of this conjugation, such compounds possess not only the properties of the individual functional groups, but certain other properties besides.

Structure and properties

C C C O

Unsaturated carbonyl compound Conjugated system

The general ways to make compounds of this kind includes: the aldol condensation,; dehydrohalogenation of a-halo acids and the Perkin condensation, and Knovenagel condensation.

Preparation

Examples:

Acraldehyde (acrolein) (propenal) :

Dehydration of glycerol: By heating glycerol with potassium hydrogen sulphate or with conc. Sulfuric acid.

H2C

HC

H2C

OH

OH

OH

conc. H2SO4

-2H2OH2C HC CHO

Oxidation of allyl alcohol using MnO2:

MnO2 H2C HC CHOH2C HC CH2OH

By passing acetaldehyde and formaldehyde vapours over sodium silicate as a catalyst.

Na2SiO4 H2C HC CHOH3C CHO HCHO+Heat

By direct oxidation of propylene:

SeO2 H2C HC CHOoxidation

H2C HC CH3

By pyrolysis of diallyl ether:

H2C HC CHOCH2CHH2COH2C HC CH2

Crotonaldehyde H3C HC HC CHO

It is prepared from acetaldehyde by aldol condensation:

H3C HC HC CHO2 H3C HCO NaOH H3C HC H2C CHO

OH-H2O

Interaction of functional group

These compounds undergo both electrophilic and nucleophilic addition according to the

following:

Electrophilic Addition

C C G ++

Y C C G

Y+

C C G

Y+

G releases electrons: activates G withdraws electrons: deactivates

The C=O, -COOH, -COOR, and -CN groups are powerfully electron -withdrawing groups, and therefore would be expected to deactivate a carbon -carbon double bond toward electrophilic addition. This is found to be true:

-­unsaturated ketones, acids, esters, and nitriles are in general less reactive than simple alkenes toward reagents like bromine and the hydrogen halides.

But this powerful electron withdrawal, which deactivates a carbon-carbon double bond toward electrophilic addition, at the same time activates­toward nucleophilic addition. As a result, the carbon-carbon double bond of an -­unsaturated ketone, acid, ester, or nitrile is susceptible to nucleophilic attack, and undergoes a set of reactions, nucleopbilic addition, that is uncommon for the simple alkenes. This reactivity toward nucleophiles is primarily due, not to a simple inductive effect of these substituents, but rather to their conjugation­with­the carbon-carbon double bond.

Examples:

+ HCl(gas)CH2 CH CH O

Acrolein

-10oCH2 CH CH O

Cl H-Chloropropionaldehyde

+ H2O H2SO4,100o

-Hydroxypropionic acid

CH2 CH C OHO

Acrylic acid

CH2 CH C OHO

OH H

+ HBr(gas) 20o

-Bromobutyric acid

CH CH C OHO

CH3

Crotonic acid

CH CH C OHO

CH3

Br H

H2SO4CH3 C CH C O

CH3 CH3

Mesityl Oxide

+ CH3OH CH3 C CH2 C O

CH3 CH3

OCH3

4-Methoxy-4-methyl-2-pentanone

The model of electrophilic addition could be explained in the following Scheme:

+

+

+C C C O

-Unsturatedcarbonyl compound

H

C C C OH More stable: actual intermediate

C C C O

H +

I

II

Intermediate I is the more stable, since the positive charge is carried by carbon atoms alone, rather than partly by the higher electronegative oxygen atom.

In the second step of addition, a negative ion or basic molecule attaches itself either to the carbonyl carbon or the b-carbon of the hybrid ion 1.

+

+

ZC C C OH

actually formedC C C OH

Z

I

III:

C C C OH

ZUnstable

Of the two possibilities, only addition to the b-carbon yields a stable product (Ill), which is simply the enol form of the saturated carbonyl compound. The enol form then undergoes tautomerization to the keto form to give the observed product (IV).

C C C O-Unsturatedcarbonyl compound

C C C OH

Z

HC C C OH

Carbocation

I

Z:

C C C O

Z H

IIIEnol formKeto

form

IV

Nucleophilic addition

Aqueous sodium cyanide converts a,b-unsaturated carbonyl compounds into b-cyano carbonyl compounds. The reaction amounts to addition of the elements of HCN to the carbon-

carbon double bond. For example:

NaCN(aq.)CH CH C C6H5

OC6H5 CH C C C6H5

O

C6H5

CN H

H

Benzalacetophenone3-Cyano-1 ,3-diphenyl- I -propanone

NaCN(aq.)CH CH C OC2H5

OCH3 CH C C OC2H5

O

CH3

CN H

H

Ethyl crotonateEthyl -Cyanobutyrate

Ammonia or certain derivatives of ammonia (amines, hydroxylamine, phenyl hydrazine, etc.) add to a,b-unsaturated carbonyl compounds to

yield b-amino carbonyl compounds. For example:

CH3 C CH C O

CH3 CH3

Mesityl Oxide

+ CH3NH2 CH3 C CH2 C O

CH3 CH3

NHCH3

4-(N-Methylamino-4-methyl)-2-pentanone

NH2OHCH CH C OH

OCH CH2 C OH

O

NHOHCinnamic acid

3-(N- Hydroxylamino)-3-phenylpropanoic acid

These reactions are believed to take place by the following mechanism:

+C C C O-Unsturatedcarbonyl compound

C C C O

ZI

Z:-

(Step I)

+ H

I

C C C O

Z H

Enol form

Ketoform

C C C O

Z -(Step 2)

+

C C C OH

Z

The Michael addition:

Of special importance in synthesis is the nucleophilic addition of carbanions to a,b -unsaturated carbonyl

compounds known as the Michael addition. Like the reactions of carbanions , it results in formation of

carbon-carbon bonds. For example:

C6H5 CH CH C O

C6H5

Benzalacetophenone Ethyl malonate

+piperidine

CH(COOC2H5)2

C6H5 CH CH2 C O

C6H5

CH2(COOC2H5)2

C6H5 CH CH C OEt

O

Ethyl malonate

+ CH2(COOC2H5)2

Ethyl cinnamate

OC2H5-

CH(COOC2H5)2

C6H5 CH CH2 C OEt

O

CH3 CH CH C OEt

O

Ethyl malonate

+ CH2(COOC2H5)2OC2H5-

CH(COOC2H5)2

CH3 CH CH2 C OEt

O

Ethyl crotonate

+ CH2COOC2H5

CNOC2H5-

Ethyl cyanoacetate

CH2 C C OEt

OCH3

CHCOOC2H5

CN

CH2 CH C OEt

CH3 O

Ethyl methacrylate

The Michael addition is believed to proceed by the following mechanism (shown for

malonic ester):

+CH2(COOC2H5)2-

Base :HBase : ++ CH(COOC2H5)2

(1)

C C C O-+ CH(COOC2H5)2

-(2)

Nucleophilicreagent

C C C O

CH(COOC2H5)2

+

I

(3)

-C C C O

CH(COOC2H5)2

Base :H + C CH C O

CH(COOC2H5)2

+ Base :

The Diels-Alder reaction-Unsaturated carbonyl compounds undergo an

exceedingly useful reaction with conjugated dienes, known as the Diels-Alder reaction. This is an addition reaction in which C-I and C-4 of the conjugated diene system become attached to the doubly-bonded carbons of the unsaturated carbonyl compound to form a six membered ring.

C

CC

O

+C

C

C

CC

O

Dienophile(Greek: diene-IovingDiene

Adduct Six-membered ring

+ O

O

O

HC

HC

CH2

CH2

Maleic anhydride1,3-Butadiene

O

O

Ocis-I,2,3,6- Tetrahydrophthalic

anhydride

HC

CH

H

C

O

H+HC

HC

CH2

CH2

1,3-Butadiene Acrolein 1,2,3,6- Tetrahydrobenzaldehyde

O

H

+HC

HC

CH2

CH2

1,3-Butadiene p-Benzoquinone

O

O

5,8,9,10- Tetrahydro-1 ,4-naphthoquinone

O

O

1,3-Butadiene

O

O

1,4,5,8,11,12,13,14- Octahydro-9,10-Anthraquinone