Post on 29-Jan-2016
PhenolsPhenolsPhenolsPhenols
Infrared Spectrum of Infrared Spectrum of pp-Cresol-CresolInfrared Spectrum of Infrared Spectrum of pp-Cresol-Cresol
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (Chemical shift (, ppm), ppm)
Proton NMRProton NMRProton NMRProton NMR
CCHH33HHOO
HH HH
HHHH
OOCHCH33
129.5129.5
114.0114.0
159.7159.7
120.7120.7
Oxygen of hydroxyl group deshields carbonOxygen of hydroxyl group deshields carbonto which it is directly attached.to which it is directly attached.
The most shielded carbons of the ring are those thatThe most shielded carbons of the ring are those thatare ortho and para to the oxygen.are ortho and para to the oxygen.
1313C NMRC NMR1313C NMRC NMR
OOHH
129.8129.8
115.5115.5
155.1155.1
121.1121.1
128.5128.5
Prominent peak for molecular ion. Most intense Prominent peak for molecular ion. Most intense peak in phenol is for molecular ion.peak in phenol is for molecular ion.
m/z m/z 9494
Mass SpectrometryMass SpectrometryMass SpectrometryMass Spectrometry
OHOH••++
••••
The OH group of phenols allows hydrogen bondingThe OH group of phenols allows hydrogen bondingto other phenol molecules and to water.to other phenol molecules and to water.
Physical PropertiesPhysical PropertiesPhysical PropertiesPhysical Properties
HH OOOO
Hydrogen Bonding in PhenolsHydrogen Bonding in PhenolsHydrogen Bonding in PhenolsHydrogen Bonding in Phenols
Physical PropertiesPhysical PropertiesPhysical PropertiesPhysical Properties
CC66HH55CHCH33 CC66HH55OHOH CC66HH55FF
Molecular weightMolecular weight 9292 9494 9696
––9595 4343 ––4141Melting point (°C)Melting point (°C)
BoilingBoilingpoint (°C,1 atm)point (°C,1 atm)
111111 132132 8585
Solubility inSolubility inHH22O (g/100 mL,25°C)O (g/100 mL,25°C)
0.050.05 8.28.2 0.20.2
Acidity of PhenolsAcidity of Phenols
Their most characteristic propertyTheir most characteristic property
CompareCompareCompareCompare
OO HH••••••••
ppKKaa = 10 = 10++HH ++
OO••••••••
••••––
CHCH33CHCH22OO HH••••
••••
ppKKaa = 16 = 16++HH ++ CHCH33CHCH22OO
••••
••••
––••••
Delocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ion
•••• OO••••
HH
HH
HH
HH
HH
••••––
•••• OO••••
HH
HH
HH
HH
HH
––••••
Delocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ion
•••• OO••••
HH
HH
HH
HH
HH
––••••
•••• OO••••
HH
HH
HH
HH
HH––••••
Delocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ion
•••• OO••••
HH
HH
HH
HH
HH––••••
•••• OO••••
HH
HH
HH
HH
HH
––••••
Phenols are converted to phenoxide ionsPhenols are converted to phenoxide ionsin aqueous basein aqueous base
Phenols are converted to phenoxide ionsPhenols are converted to phenoxide ionsin aqueous basein aqueous base
OO HH••••••••
OO••••••••
••••––
++ HOHO–– ++ HH22OO
stronger acidstronger acid weaker acidweaker acid
Substituent EffectsSubstituent Effectson theon the
Acidity of PhenolsAcidity of Phenols
Substituent EffectsSubstituent Effectson theon the
Acidity of PhenolsAcidity of Phenols
QuestionQuestionQuestionQuestion
Which one of the following has the lowest pWhich one of the following has the lowest pKKaa??
A)A) B)B)
C)C) D)D)
Electron-releasing groups have little or no effectElectron-releasing groups have little or no effectElectron-releasing groups have little or no effectElectron-releasing groups have little or no effect
OOHH
CHCH33
OOHH OOHH
OCHOCH33
ppKKaa:: 1010 10.310.3 10.210.2
Electron-withdrawing groups increase acidityElectron-withdrawing groups increase acidityElectron-withdrawing groups increase acidityElectron-withdrawing groups increase acidity
OOHH
ClCl
OOHH OOHH
NONO22
ppKKaa:: 1010 9.49.4 7.27.2
Effect of electron-withdrawing groups is mostEffect of electron-withdrawing groups is mostpronounced at ortho and para positionspronounced at ortho and para positions
Effect of electron-withdrawing groups is mostEffect of electron-withdrawing groups is mostpronounced at ortho and para positionspronounced at ortho and para positions
OOHH
NONO22
OOHH
NONO22
OOHH
NONO22
ppKKaa:: 7.27.2 8.48.4 7.27.2
Effect of strong electron-withdrawing groupsEffect of strong electron-withdrawing groupsis cumulativeis cumulative
Effect of strong electron-withdrawing groupsEffect of strong electron-withdrawing groupsis cumulativeis cumulative
OOHH
NONO22
OOHH
NONO22
NONO22
OOHH
NONO22
NONO22
OO22NN
ppKKaa:: 7.27.2 4.04.0 0.40.4
Picric acidPicric acid
Resonance Resonance Resonance Resonance
•••• OO••••
NN
HH
HH
HH
HH
••••OO OO
••••
••••
•••••••••••• ––
++
••••
––
•••• OO••••
NN
HH
HH
HH
HH
••••
––
OO OO
••••
••••
•••••••••••• ––
++
QuestionQuestionQuestionQuestion
Which of the following compounds is more Which of the following compounds is more acidic?acidic?
A)A) oo-Cresol-Cresol
B)B) oo-Chlorophenol-Chlorophenol
C)C) oo-Methoxyphenol-Methoxyphenol
D)D) oo-nitrophenol-nitrophenol
E) m-nitrophenolE) m-nitrophenol
Preparation of Aryl EthersPreparation of Aryl EthersPreparation of Aryl EthersPreparation of Aryl Ethers
Typical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson Synthesis
OONaNa ++ RRXX
OORR NaNaXX++SSNN22
but the other combinationbut the other combination
XX ++ RROONaNa
fails because aryl halides are normally unreactivefails because aryl halides are normally unreactivetoward nucleophilic substitutiontoward nucleophilic substitution
acetone, heatacetone, heat
ExampleExampleExampleExample
OOHH ++
(86%)(86%)
HH22CC CHCHCHCH22BrBr
KK22COCO33
OOCHCH22CHCH CHCH22
Aryl Ethers from Aryl HalidesAryl Ethers from Aryl HalidesAryl Ethers from Aryl HalidesAryl Ethers from Aryl Halides
FF
NONO22
++ KKOOCHCH33
CHCH33OHOH
25°C25°C
OOCHCH33
NONO22
++ KKFF
(93%)(93%)
nucleophilic aromatic substitution is effective nucleophilic aromatic substitution is effective with nitro-substituted (ortho and/or para) aryl with nitro-substituted (ortho and/or para) aryl halides halides
Claisen RearrangementClaisen Rearrangement
of Allyl Aryl Ethersof Allyl Aryl Ethers
Claisen RearrangementClaisen Rearrangement
of Allyl Aryl Ethersof Allyl Aryl Ethers
Allyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on Heating
OOCHCH22CHCH CHCH22
200°C200°C
OOHH
CHCH22CHCH CHCH22
(73%)(73%)
allyl group allyl group migrates to migrates to ortho positionortho position
rewrite as rewrite as
MechanismMechanismMechanismMechanism
OOCHCH22CHCH CHCH22
OO
OO
HH
keto-to-enolketo-to-enolisomerizationisomerization
OOHH
Claisen rearrangement is an example of a Claisen rearrangement is an example of a sigmatropic rearrangement. A sigmatropic rearrangement. A bond migrates bond migratesfrom one end of a conjugated from one end of a conjugated electron system electron systemto the other.to the other.
this this bond breaks bond breaks
this this bond forms bond forms
““conjugated conjugated electron system” electron system” is the allyl groupis the allyl group
Sigmatropic RearrangementSigmatropic RearrangementSigmatropic RearrangementSigmatropic Rearrangement
OO
OO
HH
QuestionQuestionQuestionQuestion
What will be the Claisen rearrangement What will be the Claisen rearrangement product of the carbon-14 labeled ether product of the carbon-14 labeled ether shown here? shown here?
A) A) B)B)
C)C) D)D)
Oxidation of Phenols:Oxidation of Phenols:QuinonesQuinones
Oxidation of Phenols:Oxidation of Phenols:QuinonesQuinones
The most common examples of phenol oxidationsThe most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. to give quinones.
(76-81%)(76-81%)
QuinonesQuinonesQuinonesQuinones
OOHH
OOHH
OO
OO
NaNa22CrCr22OO7,7, H H22SOSO44
HH22OO
The most common examples of phenol oxidationsThe most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. to give quinones.
(68%)(68%)
QuinonesQuinonesQuinonesQuinones
OO
OOAgAg22OO
diethyl etherdiethyl ether
OOHH
OOHH
CHCH33
CHCH33
AlizarinAlizarin(red pigment)(red pigment)
Some quinones are dyesSome quinones are dyesSome quinones are dyesSome quinones are dyes
OO
OO
OHOH
OHOH
maxmax
204 nm204 nm256 nm256 nm
maxmax
210 nm210 nm270 nm270 nm
maxmax
235 nm235 nm287 nm287 nm
Oxygen substitution on ring shifts Oxygen substitution on ring shifts maxmax to longer to longer
wavelength; effect is greater in phenoxide ion.wavelength; effect is greater in phenoxide ion.
UV-VISUV-VISUV-VISUV-VIS
OHOH
OO––
Vitamin KVitamin K
(blood-clotting factor)(blood-clotting factor)
Some quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomolecules
OO
CHCH33
OO CHCH33 CHCH33 CHCH33 CHCH33
CHCH33
Some quinone precursors are important in foodsSome quinone precursors are important in foodsSome quinone precursors are important in foodsSome quinone precursors are important in foods
Antioxidants can protect against the cell-Antioxidants can protect against the cell-damaging effects of free radicals. Some dietary damaging effects of free radicals. Some dietary phenolics are oxidized to quinones as free phenolics are oxidized to quinones as free radical-antioxidant traps.radical-antioxidant traps.
Eg. Reservatrol / FlavonoidsEg. Reservatrol / Flavonoids