1. 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.
α,β--Unsaturated Carbonyl Compound
O
R R'
2. 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:
4. In the α,β-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
5. C C C O
α
β
α,β−Unsaturated
carbonyl compound
Conjugated system
6.
7.
8. 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
9. 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
-2H2O
H2C HC CHO
10. Oxidation of allyl alcohol using MnO2:
MnO2
H2C HC CHO
H2C HC CH2OH
By passing acetaldehyde and formaldehyde
vapours over sodium silicate as a catalyst.
Na2SiO4
H2C HC CHO
H3C CHO HCHO
+
Heat
11. By direct oxidation of propylene:
SeO2
H2C HC CHO
oxidation
H2C HC CH3
By pyrolysis of diallyl ether:
H2C HC CHO
CH2
CH
H2C
O
H2C HC CH2
12. Crotonaldehyde
H3C HC HC CHO
It is prepared from acetaldehyde by aldol
condensation:
H3C HC HC CHO
2 H3C HCO
NaOH H3C HC H2C CHO
OH
-H2O
13. 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
14. 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:
15. α,β--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 activates toward nucleophilic addition. As
a result, the carbon-carbon double bond of an α,β--
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 conjugation with the carbon-carbon
double bond.
16. Examples:
+ HCl(gas)
CH2 CH CH O
Acrolein
-10o
CH2 CH CH O
Cl H
β-Chloropropionaldehyde
+ H2O H2SO4,100o
β-Hydroxypropionic acid
CH2 CH C OH
O
Acrylic acid
CH2 CH C OH
O
OH H
+ HBr(gas) 20o
β-Bromobutyric acid
CH CH C OH
O
CH3
Crotonic acid
CH CH C OH
O
CH3
Br H
17. H2SO4
CH3 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
α,β-Unsturated
carbonyl compound
H
C C C OH More stable:
actual intermediate
C C C O
H +
I
II
18. 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.
+
+
Z
C C C OH
actually formed
C C C OH
Z
I
III
:
C C C OH
Z
Unstable
19. 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
α,β-Unsturated
carbonyl compound
C C C OH
Z
H
C C C OH
Carbocation
I
Z
:
C C C O
Z H
III
Enol form
Keto
form
IV
20. 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
O
C6H5 CH C C C6H5
O
C6H5
CN H
H
Benzalacetophenone
3-Cyano-1 ,3-diphenyl- I -propanone
21. NaCN(aq.)
CH CH C OC2H5
O
CH3 CH C C OC2H5
O
CH3
CN H
H
Ethyl crotonate
Ethyl β-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
22. NH2OH
CH CH C OH
O
CH CH2 C OH
O
NHOH
Cinnamic acid
3-(N- Hydroxylamino)-3-phenylpropanoic acid
These reactions are believed to take
place by the following mechanism:
+
C C C O
α,β-Unsturated
carbonyl compound
C C C O
Z
I
Z
:
-
(Step I)
23. + H
I
C C C O
Z H
Enol form
Keto
form
C C C O
Z -
(Step 2)
+
C C C OH
Z
24. 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
25. 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)2
OC2H5
-
CH(COOC2H5)2
CH3 CH CH2 C OEt
O
Ethyl crotonate
+ CH2COOC2H5
CN
OC2H5
-
Ethyl cyanoacetate
CH2 C C OEt
O
CH3
CHCOOC2H5
CN
CH2 CH C OEt
CH3 O
Ethyl methacrylate
26. The Michael addition is believed to proceed
by the following mechanism (shown for
malonic ester):
+
CH2(COOC2H5)2
-
Base
:
H
Base
: +
+ CH(COOC2H5)2
(1)
C C C O
-
+ CH(COOC2H5)2
-
(2)
Nucleophilic
reagent
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
:
27. The Diels-Alder reaction
α,β-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
C
C
O
+
C
C
C
C
C
O
Dienophile
(Greek: diene-Ioving
Diene
Adduct
Six-membered ring
