Transcript Carey Chapter 4 Alcohols, Alkyl Halides

Alcohols, enols and phenols
Classification
Alcohols and alkyl halides are classified as
primary
secondary
tertiary
according to their "degree of substitution."
Degree of substitution is determined by counting
the number of carbon atoms directly attached to
the carbon that bears the halogen or hydroxyl group.
Classification
H
CH3CH2CH2CH2CH2F
OH
primary alkyl halide
secondary alcohol
CH3
CH3CHCH2CH2CH3
Br
secondary alkyl halide
CH3CCH2CH2CH3
OH
tertiary alcohol
IUPAC Nomenclature
of Alcohols
Functional Class Nomenclature of Alcohols
Name the alkyl group and add "alcohol" as a
separate word.
CH3CH2OH
CH3
CH3CCH2CH2CH3
CH3CHCH2CH2CH2CH3
OH
OH
Functional Class Nomenclature of Alcohols
Name the alkyl group and add "alcohol" as a
separate word.
CH3CH2OH
Ethyl alcohol
CH3CHCH2CH2CH2CH3
OH
1-Methylpentyl alcohol
CH3
CH3CCH2CH2CH3
OH
1,1-Dimethylbutyl
alcohol
Substitutive Nomenclature of Alcohols
Name as "alkanols." Replace -e ending of alkane
name by -ol.
Number chain in direction that gives lowest number
to the carbon that bears the —OH group.
CH3CH2OH
CH3
CH3CCH2CH2CH3
CH3CHCH2CH2CH2CH3
OH
OH
Substitutive Nomenclature of Alcohols
Name as "alkanols." Replace -e ending of alkane
name by -ol.
Number chain in direction that gives lowest number
to the carbon that bears the —OH group.
CH3CH2OH
Ethanol
CH3CHCH2CH2CH2CH3
OH
CH3
CH3CCH2CH2CH3
OH
2-Methyl-2-pentanol
2-Hexanol
Substitutive Nomenclature of Alcohols
OH
CH3
CH3
OH
Hydroxyl groups outrank
alkyl groups when
it comes to numbering
the chain.
Number the chain in the
direction that gives the
lowest number to the
carbon that bears the
OH group
Substitutive Nomenclature of Alcohols
OH
6-Methyl-3-heptanol
CH3
CH3
5-Methyl-2-heptanol
OH
Dipole Moments
alcohols and alkyl halides are polar
 = 1.7 D
 = 1.9 D
Effect of Structure on Boiling Point
CH3CH2OH
Molecular
weight
46
Boiling
point, °C
+78
Dipole
moment, D
1.7
Highest boiling point;
strongest intermolecular
attractive forces.
Hydrogen bonding is
stronger than other
dipole-dipole attractions.
Hydrogen bonding in ethanol
Reaction of Alcohols with Acyl Chlorides
O
ROH +
R'CCl
O
R'COR +
high yields
not reversible when carried out
in presence of pyridine
HCl
Esterification
O
ROH +
H+
O
R'COR +
R'COH
a condensation reaction
called Fischer esterification
acid catalyzed
reversible
H2O
Reaction of Alcohols with Acid Anhydrides
O O
ROH + R'COCR'
O
R'COR +
analogous to reaction with acyl chlorides
O
R'COH
Esters of Inorganic Acids
ROH + HOEWG
ROEWG + H2O
EWG is an electron-withdrawing group
+
HONO2
(HO)2SO2
(HO)3P
–
O
Oxidation of Alcohols
Primary alcohols
O
O
RCH2OH
RCH
RCOH
Secondary alcohols
OH
O
RCHR'
RCR'
from H2O
Enzyme-catalyzed
CH3CH2OH
+
NAD
+
(a coenzyme)
alcohol
dehydrogenase
CH3CH
O
+ NAD
H
+
H+
Cleavage of Vicinal Diols by Periodic Acid
C
HO
HIO4
C
OH
C
O + O
C
Enols and Enolates
Enol-oxo tautomerism
OH
O
CH3CH
H2C
K = 3 x 10-7
OH
O
CH3CCH3
CH
H2C
CCH3
K = 6 x 10-9
Mechanism of Enolization (In general)
••
O ••
R2C
CR'
H
••
•• O
R2C
CR'
H
Enol Content
OH
O
R2CHCR'
R2C
keto
CR'
enol
percent enol is usually very small
keto form usually 45-60 kJ/mol more stable
than enol
Phenols
Nomenclature
OH
CH3
5-Chloro-2-methylphenol
Cl
named on basis of phenol as parent
substituents listed in alphabetical order
lowest numerical sequence: first point of
difference rule
Nomenclature
OH
OH
OH
OH
OH
OH
1,2-Benzenediol
1,3-Benzenediol
1,4-Benzenediol
(common name:
pyrocatechol)
(common name:
resorcinol)
(common name:
hydroquinone)
Nomenclature
OH
p-Hydroxybenzoic acid
CO2H
name on basis of benzoic acid as parent
higher oxidation states of carbon outrank
hydroxyl group
Structure of Phenol
phenol is planar
C—O bond distance is 136 pm, which is
slightly shorter than that of CH3OH (142 pm)
Physical Properties
The OH group of phenols allows hydrogen
bonding
to other phenol molecules and to water.
Hydrogen Bonding in Phenols
O H
O
Acidity of Phenols
most characteristic property of
phenols is their acidity
Compare
••
•• O
•• –
•• O ••
H
Ka = 10-10
••
CH3CH2O
••
+ +
H
Ka = 10-16
H
+ +
H
•• –
CH3CH2O ••
••
Effect of strong electron-withdrawing groups
is cumulative
OH
OH
OH
NO2
NO2
NO2
Ka: 7 x 10-8
1 x 10-4
NO2
O2N
NO2
4 x 10-1
Example: Thymol
OH
CH3
CH(CH3)2
Thymol
(major constituent of oil of thyme)
Example: 2,5-Dichlorophenol
OH
Cl
Cl
2,5-Dichlorophenol
(from defensive secretion of
a species of grasshopper)
O-Acylation
O
OH
OC(CH2)6CH3
O
+ CH3(CH2)6CCl
(95%)
in the absence of AlCl3, acylation of the
hydroxyl group occurs (O-acylation)
Typical Preparation is by Williamson Synthesis
ONa + RX
SN2
OR + NaX
Example
acetone
ONa + CH3I
heat
OCH3
(95%)
Quinones
The most common examples of phenol oxidations
are the oxidations of 1,2- and 1,4-benzenediols
to give quinones.
OH
O
Na2Cr2O7, H2SO4
H2O
OH
O
(76-81%)
Quinones
The most common examples of phenol oxidations
are the oxidations of 1,2- and 1,4-benzenediols
to give quinones.
OH
O
OH
O
Ag2O
diethyl ether
CH3
CH3
(68%)
Some quinones are dyes
O
OH
OH
O
Alizarin
(red pigment)
Some quinones are important biomolecules
O
CH3
CH3O
CH3O
n
O
Ubiquinone (Coenzyme Q)
n = 6-10
involved in biological electron transport
Some quinones are important biomolecules
O
CH3
CH3
O
CH3
CH3
CH3
Vitamin K
(blood-clotting factor)
CH3