biological chemistry first year organic chemistry lecture seven aldehydes ketones convenor : dr....
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Biological ChemistryFIRST YEAR ORGANIC CHEMISTRY
Lecture SevenAldehydes & Ketones
Convenor : Dr. Fawaz Aldabbagh
Aldehydes and Ketones
O 1s2, 2s2 2p2 2p1 2p1
3 sp2 orbitals
CH
RO C
R
RO
Aldehyde Ketone
CH
HO
lone Pairs
bond - two overlapping 2p orbitals
bond bond- overlapping 1s H-orbital and sp2 C-orbital
C OH3C
H118o
121oC C
H
H
H
H118o
121o
C OH3C
HC O
H3C
HResonance Structures
Most Reactive Group –
electrons + polarisation
Useful in Synthesis
Names al – aldehydes, one - ketones
C OH
HC O
H3C
HC O
CH3CH2
HC O
CH3CH2CH2CH2
H
Methanal(formaldehyde)
Ethanal(acetaldehyde)
Propanal Pentanal
OH
H O
H
H
Benzaldehydetrans-Cinnamaldehyde
Formalin, 35-40% formadehyde in waterPreservative that reacts with proteins causing them to resist decayCoelacanth, “prehistoric fish”
OH
Acrolein (2-propenal)
S
HThiopropionaldehyde (propanethiol)
- lachrymator from chopped onion- lachrymator and pleasant "odour" from barbacuing meat
Propanone(ACETONE)
Butanone
AcetophenoneBenzophenone
O
H3C CHCH2
CH3
CH3
3-Methyl-2-pentanone
O H
OCH3
OH
Vanillin
CH3
O
Carvone(spearmint flavour)
O O
H3C CH3
Butadione(butter flavour)
O
H3C CH3
O
CH3
O
O
H3C CH2
CH3
Carbonyls readily undergo Nucleophilic Attack
cis and trans isomers possible
- H2OC O N N
H
H
H
H+ C N N
H
H
Hydrazine Hydrazone
ANHYDROUS
OC
RNH2
OCNHH
R
OCNH R
H
OCNH R
H
CN
R
- H2O
Imine
The reaction is acid-catalysed
H+ + H2O Equilibrium Reactions
Other Condensation ReactionsR
CH
O H3C OH
H3C OH
H+
+R
CH
OCH3
OCH3- H2O
Dimethoxy ACETAL
C O + NNHH
HNO2
O2N
NNH
NO2
O2N
H
H3C
2,4-Dinitrophenylhydrazine
2,4-DinitrophenylhydrazoneAcetaldehyde-
Acid-Catalysed Acetal Formation
Reversed with acid and water
Acetal is stable under basic conditions
O
H R
H+
O
R
H
OHH3C
OCH RO
H
H CH3
OCH RO
H
CH3Hemiacetal
- H2O
- H+
OCH3COCH3
H
R
OCH RO
H
CH3
H
OHH3CH
- H+
OCH3COCH3
H
RAcetal
+ H+
Addition of Hydrogen Cyanide
OOH
CN
NaCN + NH4Cl NaCl + NH3 + HCN
cyclohexanone
Nucleophilic addition reactions
OC
R H+ HCN
HC
R
OH
CN
C O
-CN
CyanohydrinHC
R
O
CNH CN
Professor Victor Grignard (1912 Nobel Prize)Developed this chemistry with Professor P. A. Barbier
CR OH
ProtonationH
H2OAlcohol
CR X
H
H
X = I or Br
CH
HMgXR RCH2
MgX
Grignard Reagent
Mg
Ether
CR X
H
H
X = I or Br
CH
HLiR RCH2
Li
Organolithium Reagent
Li
Ether
C O
R Li
CR O LiADDITION
Examples MgBr
C OH
H
EtherCH
HO MgBr
H3O+
CH
HO H
BenzylalcoholC O MgBr+
Ether
C OH
Triphenylmethanol
Benzyl GroupPhenyl, Ph Group
Ph
2. H3O+
-Hydrogens next to Carbonyl Groups are relatively acidic
OC
R CH
C
H
Hydrogen, pKa = 19-20
Hydrogen, pKa = 40-50
Keto-Enol TautomerismThe negative charge is delocalisedO OH
98.8%1.2%
O
H3C CH3
OH
H3C CH2
>99%
C=O bond stronger than C=C bond so equilibrium lies towards keto-tautomerEnol formation can be acid or base catalysed
OC
R CH
B
OC
R C
OC
R C
- HB
Resonance StabilizedOC
RC
OC
R CH
B
- HBOC
R C
H
Enol
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