Transcript ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO …

ALDEHYDES AND KETONES
STRUCTURE
Aldehyde
O
C
R
H
R = H, alkyl, aryl
Ketone
O
C
R
R'
R and R' = alkyl or aryl
R and R' cannot be hydrogen!
NOMENCLATURE
IUPAC Nomenclature of Ketones
• Choose the longest continuous carbon chain that
contains the carbonyl carbon
• Number from the end of the chain closest to the
carbonyl carbon
• Ketone ending is -one
Do the ketones section of Organic Nomenclature
program!
EXAMPLES
O
C
CH 3
CH 2
CH 2
CH 3
2-Pentanone
O
CH3
C
CH2
CH2
CH
CH3
CH2
CH3
4-Ethyl-3-hexanone
O
CH
CH3
CH3
3-Isopropylcyclopentanone
KETONES
Common, or Trivial, Names
• Name each group attached to the carbonyl group
as an alkyl group
• Combine into a name, according to the pattern:
alkyl alkyl’ ketone
NOTE: This is not all one word!
Example of Common Names
O
C
CH 3
CH 2
CH 2
CH 3
Methyl propyl ketone
O
CH3
C
CH2
CH3
CH2
Diethyl ketone
SPECIAL CASES
O
O
C
C
CH3
CH3
dimethyl ketone
diphenyl ketone
benzophenone
acetone
A common laboratory
solvent and cleaning
agent
KNOW
THESE
O
C CH3
methyl phenyl ketone
acetophenone
IUPAC Nomenclature of Aldehydes
• Choose the longest continuous carbon chain that
contains the carbonyl carbon
• Number from the end of the chain closest to the
carbonyl carbon (carbon #1!)
• Aldehyde ending is -al
Do the aldehydes section of Organic Nomenclature
program.
EXAMPLES
H3C
CH2
CH2
CH2
C
aldehyde group is
always carbon 1
O
H
pentanal
Cl
4
CH3
3
CH
1
2
C
CH
CH3
O
H
2-chloro-3-methylbutanal
Common Names of the Aldehydes
H
O
O
O
C
C
C
CH3
H
Formaldehyde
1
H
H3C CH2
Acetaldehyde
2
H
Propionaldehyde
3
O
O
C
C
H3C CH2 C
H
H3C CH2 CH2 C
Butyraldehyde
Valeraldehyde
4
5
H
O
C
H3C CH2 CH2 CH2 CH2
Caproaldehyde
6
H
RECOGNIZE
THESE
O
SPECIAL CASES
C
H
H
O
C H
formaldehyde
O
benzaldehyde
C
H
CH3
acetaldehyde
KNOW
THESE
Forming Common Names of Aldehydes
USE OF GREEK LETTERS
O
C
C
C
C
C
C
C

…….
H
 is always the end of the chain, no matter how long
CHO
CHO
Cl
-chlorocaproaldehyde
( -chlorohexanal )
Cl
-chlorocaproaldehyde
( -chlorohexanal )
REACTIVITY OF THE C=O GROUP
NUCLEOPHILIC ADDITION
GENERALIZED CHEMISTRY
THE CARBONYL GROUP
nucleophilic
at oxygen
.. O:
C
electrophiles
add here
H+
or E+
.. :O :
+
C
+
Nu:
nucleophiles
attack here
electrophilic
at carbon
NUCLEOPHILIC ADDITION TO C=O
MECHANISMS
IN ACID AND IN BASE
Nucleophilic Addition to Carbonyl
Basic or Neutral Solution
.. _
: O:
..
O:
-:Nu
+
slow
C
C
an
alkoxide
ion
Nu
.. _
: O:
..
:O H
fast
C
Nu
+
H2O
C
or on adding acid
Nu
Good nucleophiles
and strong bases
(usually charged)
BASIC SOLUTION
Nucleophilic Addition to Carbonyl
Acid Catalyzed
+
:O
..
O:
C
+
+
H
fast
C
..
:O
.. +
O H
H
slow
+
C
more reactive to
addition than the unprotonated precursor
H
:Nu
C
Nu
Acid catalysis speeds the rate of
addition of
weak nucleophiles and
weak bases (usually uncharged).
(+)
ACIDIC SOLUTION
pH 5-6
stronger acid
protonates the
nucleophile
CYANOHYDRINS
Addition of Cyanide
Buffered to pH 6-8
:C N:
.. _
:O :
:O :
_
R
C
R
+
CN
R
C
R
CN
.. _
:O :
R
C
CN
..
:O
R
+
H2O
R
C
H
R
CN
a cyanohydrin
-,
In acid solution there would be littleACN
cyanohydrin
and HCN (g) would be a problem (poison).
CYANIDE ION BONDS TO HEMOGLOBIN
..
N
CYANIDE IS
Cyanide bonds
IS A POISON
(irreversibly) to the
C
..
CH3
H3C
site (Fe II) where
oxygen usually bonds.
N
N
You die of
suffocation lack of oxygen.
Fe
N
N
CH3
H3C
CH2CH2COOH
CH2CH2COOH
HCN is a gas that you can easily breathe into your lungs.
ORGANOMETALLICS
Synthesis of Alcohols
Addition of Organometallic Reagents
.. _
+
:O: M
:O :
R
M
(R-MgBr)
+
ether
R
C
R
(R-Li)
R
C
R
R
:R -
H2O
+
H
These reagents cannot
exist in acid solution
..
:O
R
alcohol
C
R
workup
step
H
R
+
M (OH)x
Summary of Reactions of
Organometallics with
Carbonyl Compounds
All review
to you
• Organometallics with ketones yield
tertiary alcohols
• Organometallics with aldehydes yield
secondary alcohols
• Organometallics with formaldehyde yield
primary alcohols.
• Organometallics with carbon dioxide yield
carboxylic acids.
etc.
HYDRATES
Addition of Water
O
O H
+
H
+
C
H2O
R
R'
R
aldehyde or ketone
favored
R
C
O H
O
R'
C
R
+
R'
R'
O H
a hydrate
hydrates are unstable
and cannot be isolated
in most cases
most hydrates revert to an aldehyde
or ketone as soon as they form
O H
C
H2O
ACID CATALYSIS
RECALL
H
+
O
H
..
.. H
+
:O
:O H
..
:O H
+
Acid catalysis enhances the reactivity
of the carbonyl group - nucleophilic
addition proceeds more easily.
:Nu
weak nucleophiles
can react
Water is a weak nucleophile.
WATER ADDS TO THE CARBONYL GROUP OF
ALDEHYDES AND KETONES TO FORM HYDRATES
H
catalyzed by a
trace of acid
+
..
:O
H
O H
..
..
+ H
:O
..
H
:O
C
C
H
..
O
..
H
H
H
O+
..
..
O
..
:O
..
H
H
a hydrate
H
H
+
H
for most compounds the equilibrium
favors the starting materials
and you cannot isolate the hydrate
H
:O
O H
..
MICROREVERSIBILITY:
In a reaction where all steps are
reversible, the steps in the reverse
reaction are the same as those in
the forward reaction, reversed!
ISOTOPE EXCHANGE REVEALS THE PRESENCE
OF THE HYDRATE
O18
O
R
+H2O18
R
+ H2O
H+
18
R
excess
O H
R C R
18 O
H
R
an excess of H2O18
shifts the equilibrium
to the right
-H2O
exchange shows the
presence of a symmetric
intermediate
SOME STABLE HYDRATES
these also indicate that hydrates are possible

Cl

Cl
C
+Cl

Cl
O
H
chloral
120o expected
60o required
O
sp2
cyclopropanone
Cl
OH
C
OH
Cl H
chloral hydrate
OH
sp3 OH
109o expected
60o required
cyclopropanone
hydrate
SOME ADDITIONAL STABLE HYDRATES
O
O
O
H C C
H
glyoxal
O
H
C C OH
H
O
O
Ph C C
phenylglyoxal
H
Ph
OH
OH
C C OH
H
ACETALS AND
HEMIACETALS
ACID CATALYSIS
RECALL
H
+
O
H
..
.. H
+
:O
:O H
..
:O H
+
Acid catalysis enhances the reactivity
of the carbonyl group - nucleophilic
addition proceeds more easily.
:Nu
weak nucleophiles
can react
Alcohols are weak nucleophiles.
Addition of Alcohols
TWO MOLES OF ALCOHOL WILL ADD
addition of one mole
O
H+
R C R' + ROH
O H
R C R'
hemiketal
O R
addition of second mole
O H
R C R'
O R
H+
+
ROH
O R
R C R' + H O
O R
H
an aketal
The equilibria normally favor the aldehyde or ketone starting
material, but we will show how they can be made.
ACETALS AND HEMIACETALS
R
C O
ROH
H aldehyde
R
C
H
OH ROH
OR
hemiacetal
R
C O
R
ketone
ROH
R
C
R
OH ROH
OR
R
OR
C
H
OR
acetal
R
OR
C
R
OR
(hemiketal)*
(ketal)*
*older term
*older term
..
R OH
+ H 2S O4
R
O
+
H
Like a
hydronium
ion
H
R
+
..
H O
:O
..
H
R C R
ACID CATALYZED
FORMATION OF A
HEMIACETAL
..
+
:O H
R C R
H
..
O
..
R C R
H
R
first
addition
H
:O
O+
..
R
..
H
..
:
R O
H
:O
Normally the starting
material is favored but a second molecule
of alcohol can react
if in excess (next slide)
H
R C R
hemiacetal
O
: ..
R
+ R O+
..
H
FORMATION OF THE ACETAL ( from the hemiacetal )
remove
R
H O
+
..
H
H
..
H
:O H
..
R C R
H
O
+
R C R
:O
..
: O..
R
..
O
..
H
H
:O
..
second
addition
R
R C R
R C R
:O +
:O
SN1
R
R
+
R
hemiacetal
..
..
+ H
:
R O
H
:O R
R
H
R C R
:O
..
R
O:
H
..
O R
+
R C R
:O
..
acetal
R
Resonance
stabilized
carbocation
STABILITY OF ACETALS AND HEMIACETALS
Most hemiacetals are not stable, except for those of sugars
(see later).
Acetals are not stable in aqueous acid, but they are stable to
aqueous base.
AQUEOUS
ACID
AQUEOUS
BASE
C
OR H2SO4
OR
H2O
OR NaOH
C
OR H2O
ROH
C O +
ROH
no reaction
ADDITION OF WATER AND ALCOHOLS
WATER
O
H2O
HO
OH
C
hydrate
ALCOHOLS
R-O-H
O
R-O-H
HO
RO
OR
C
H2O
hemiacetal
RO
OR
OR
H+
H2O
H2O
NaOH
O
+2 ROH
no reaction
acetal
acetals are
stable to base
but not to
aqueous acid
REAKSI OKSIDASI
OKSIDASI ALDEHID DAN KETON
• Keton tidak mudah dioksidasi
• Aldehid sangat mudah dioksidasi, menjadi
asam karboksilat
Zat pengoksidasi : KMnO4, H, H2O
Reaksi Reduksi
Reaksi Reduksi
• Reduksi aldehid menghasilkan alkohol primer
• Reduksi keton menghasilkan alkohol sekunder
• Zat pereduksi:
H2, katalis
Zn/Hg, HCl
Reaksi Adisi-eliminasi
Reaksi Adisi-eliminasi
• Aldehid + Amina Primer
• Aldehid + Amina sekunder
• Aldehid + Amina tersier
Imina
Enamina
hidrazon
Ramalkan produk hemiasetal atau
hemiasetal siklik dari:
1. 5-hidroksi-2-heksanon dengan air
2. 1,3,4,5,6-pentahidroksi-2-heksanon
dengan air
3. propanal dengan metanol
4. Aseton dengan 1,2,3-propanatriol
Ramalkan apa produk reaksi sikloheksanon
dengan :
1. CH3NH2
2. (CH3)2NH