wk 12 c18 alcohol ,amines
TRANSCRIPT
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1818 Alcohols,Alcohols,amines andamines andrelatedrelated
compoundscompoundsPrepared by
Emma Bartle
University of Western Australia
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18.1 Alcohols18.1 Alcohols
Alcohols contain the functional group
OH, a hydroxyl group
This hydroxyl group is bonded to an sp3
hybridised carbon atom
The oxygen atom is also sp3 hybridised
Two sp3 hybrid orbitals form bonds to
carbon and hydrogen The remaining two sp3 hybrid orbitals each
contain an unshared pair of electrons
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18.1 Alcohols18.1 Alcohols
Alcohols are named the same way as
alkanes, with the following differences
The parent alkane is the longest chain ofcarbon atoms containing the OH group
Change the suffix of the parent alkane
from e to ol, and use a number to
show the location of the OH group
Name and number substituents and list
them in alphabetical order
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18.1 Alcohols18.1 Alcohols
To derive common names for alcohols,
we name the alkyl group bonded to the
OH group and add the word alcohol
Ethanol(Ethyl alcoh ol)
1-Propanol(Propy l alcoho l)
2-Propanol(Is opropy l alcoho l)
1-Butanol(Butyl alcoho l)
OH
OH
OH
OH
2-Butanol
(s ec-Bu tyl alcoho l)2-Methyl-1-propanol
(Is obutyl alcoh ol)
2-Methyl-2-propanol(t ert-Butyl alcohol )
OH
Cyclohexanol(Cyclohexyl alcoho l)
OH
OH
OH
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We classify alcohols as primary (1), secondary (2) or
tertiary (3), depending on whether the OH group is on a
primary, secondary or tertiary carbon atom.Classify each of the following alcohols as primary, secondary or tertiary.
secondary (2) tertiary (3) primary (1)
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18.1 Alcohols18.1 Alcohols
Compounds containing 2 OH groups
are named as diols
Compounds containing 3 OH groups
are named as triols
CH3
CHCH2
HO OH
CH2 CH2
OHOH
CH2 CHCH2
OHHOHO
1,2-Ethanedio lEthylene glycol
1,2-PropanediolPropylene glycol
1,2,3-Propanetrio lGlycerol, Glycerin)
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18.1 Alcohols18.1 Alcohols
Physical properties
Both the C-O and O-H bonds of an
alcohol are polar covalent
Alcohols are polar molecules
This is demonstrated for methanol below
H-
H+
H+O
H
HH
C
H
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18.1 Alcohols18.1 Alcohols
Alcohols have higher boiling points and
water solubility than hydrocarbons
CH3CH2 CH2OH
CH3CH2 CH2CH3
CH3OH
CH3CH3
CH3CH2 OH
CH3CH2 CH3
CH3CH2 CH2CH2CH2OH
HOCH2CH2CH2CH2 OH
CH3CH2 CH2CH2CH2CH3
Structural Formula Name
Molecular
Wei ht(g/mol)
Boiling
Point(C)
Solubilityin Water
methanol 32 65 infinite
ethane 30 -89 insoluble
ethanol 46 78 infinite
propane 44 -42 insoluble
1-propanol 60 97 infinite
butane 58 0 insoluble
1-pentanol 88 138 2.3 g/100 g
1,4-butanediol 90 230 infinite
hexane 86 69 insoluble
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Alcohols associate in the liquid state by
hydrogen bonding
18.1 Alcohols18.1 Alcohols
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18.1 Alcohols18.1 Alcohols
Preparation of alcohols
Alcohols can be prepared from many
functional groups
Discussed here are:
Preparation from alkenes
Preparation from haloalkanes
Reduction of carbonyl compounds Addition of Grignard reagents to carbonyl
compounds
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Preparation from alkenes Acid catalysed hydration of alkenes
Preparation from haloalkanes Nucleophilic substitution with a hydroxide ion
18.1 Alcohols18.1 Alcohols
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Reduction of carbonyl compounds
Aldehydes are reduced to primary alcohols
Ketones are reduced to secondary alcohols
Carboxylic acids and esters can be reduced to form
primary alcohols
18.1 Alcohols18.1 Alcohols
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18.2 Reactions of alcohols18.2 Reactions of alcohols
Reactions discussed here are:
Acidity of alcohols
Basicity of alcohols Reaction with active metals
Dehydration of alcohols to alkenes
Conversion of alcohols to haloalkanes
Oxidation of alcohols to aldehydes,
ketones and carboxylic acids
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18.2 Reactions of alcohols18.2 Reactions of alcohols
Acidity of alcohols
Alcohols have similar acid ionisation
constants (pKa
) to water (15.7)
Aqueous solutions of alcohols have a pH
close to that of pure water
CH3 O H O H
H
[CH3 O-
][ H3 O+]
[ CH3 OH]
CH3 O H O
H
H+
Ka
=
+ +
= .
Ka= .
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18.2 Reactions of alcohols18.2 Reactions of alcohols
The table below gives the pKa for several
low-molar-mass alcohols
( H3 )3 OH
( H3 )2 HOH
H3 H2OH
H2O
CH3 OH
CH3 COOH
HCl
Co o Ka
-7
15 5
15 7
15 9
17
18
4 8
y roge c lori e
aceticaci
me t a o l
water
et a o l
2- ro a ol
2-met yl-2- ro a ol
Str ct ral
FormulaStro ger
aci
Weaker aci
*A lso give forcom ariso are Ka
values for water,
aceticaci , a y roge c lori e
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18.2 Reactions of alcohols18.2 Reactions of alcohols
Basicity of alcohols
In the presence of a strong acid, theoxygen atom of an alcohol is a weak base
It reacts with the acid by proton transfer toform an oxonium ion
Alcohols can function as both weak acidsand weak bases
CH3 CH2 -O-H H O
H
H O
H
H
H2 SO4CH3 CH2 -O H
H
CH3 CH2 -O H
H HH
O H
Ethylo xon ium ion(pK
a-2.4)
Hydron ium i on(pK
a-1.7)
Ethanol
+
+
++
+
+
+
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18.2 Reactions of alcohols18.2 Reactions of alcohols
Reaction with active metals
Alcohols react with Li, Na, K and other
active metals to form metal alkoxides
Na is oxidised to Na+ and H+ is reduced to H2
Alkoxide ions are stronger bases than thehydroxide ion
Alkoxide ions can be used as nucleophiles in
substitution reactions
2CH3CH2OH 2Na 2CH3CH2O-Na
+ H2+ +
So iu m et oxi e
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18.2 Reactions of alcohols18.2 Reactions of alcohols
140o
yclo exa ol C clo exe e
OH+ H 2 O
H2 SO4
180oCCH3 CH2 OH
H2 SO4CH2 =CH 2 + H 2 O
+ H2 OCH3COH
CH3
CH3
50oC
H2 SO4CH3C=CH2
CH3
2- et yl ro e e
(Isobutyle e)
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18.2 Reactions of alcohols18.2 Reactions of alcohols
Oxidation of 1 and 2 alcohols
Oxidation of a 1 alcohol gives an aldehyde or
carboxylic acid, depending on the experimental
conditions
2 alcohols are oxidised to ketones
3 alcohols are not easily oxidised
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18.2 Reactions of alcohols18.2 Reactions of alcohols
The most common reagent used for the
oxidation of a 1 alcohol to carboxylic acid
and 2 alcohol to a ketone is chromic acid
CrO3 H2 OH2SO4 H2 CrO4+
Chro ic acidChro i (VI)o ide
CH3 (CH2 )6 CH2 OHCrO3
H2SO4 ,H2 OCH3 (CH2 )6 CH
O
CH3 (CH2 )6 COH
O
Octa al( ot isolated)
Octa oic acid1-Octa ol
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18.2 Reactions of alcohols18.2 Reactions of alcohols
The mild oxidising agent PCC is used to
oxidise 1 alcohols to aldehydes
CrO3 HClN N
H
CrO3 Cl
-
Py idinium chlo och omate(PCC)
Py idine
+ ++
OHPCC
CH2 Cl2H
O
Ge aniol Ge anial
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Ester formation
Condensation of alcohols with carboxylic acids,
acid chlorides or anhydrides produces esters
Alcohols can also form esters with inorganic acids,
like nitric acid
18.2 Reactions of alcohols18.2 Reactions of alcohols
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18.4 Ethers18.4 Ethers
Ethers contain an atom of oxygen bonded
to 2 carbon atoms
Oxygen is sp3
hybridised with bondangles of approximately 109.5
H
H O
H
C H
H
H
C
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18.4 Ethers18.4 Ethers
The OR group bonded to the parent
alkane is named as an alkoxy
Common names are derived by listingthe alkyl groups bonded to oxygen in
alphabetical order and adding ether
CH3
CH3
CH3 CCH3
Et 2
H
Et
E h h n
Di h h
h m h p p nm h t ert-bu h , TBE
t rans-2-E h h n
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18.4 Ethers18.4 Ethers
Cyclic ethers contain the ether oxygen
as one of the atoms in the ring
Cyclic ethers are generally known bytheir common names
E l
i
T r r
f r , THF
T r r
r
, Di
O O
O
OO
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Physical properties
Ethers are moderately polar compounds
However, only weak forces of attraction existbetween ether molecules
18.4 Ethers18.4 Ethers
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18.4 Ethers18.4 Ethers
Ethers have lower boiling points than
alcohols of similar molar mass
CH3 CH2 OH
CH3 OCH3
CH3 CH2 CH2 CH2 CH2 OH
HOCH2 CH2 CH2 CH2 OH
CH3 CH2 CH2 CH2 OCH3
CH3 CH2 CH2 CH2 OH
CH3 CH2 OCH2 CH3
CH3 OCH2 CH2 OCH3 ethylene g lycoldimethyl ethe
90 84 in ini te
8 g/100 g3574diethyl ethe
1-butanol 74 117 7.4 g/100 g
slight7188butyl methyl e the
in ini te230901,4-butanediol
2.3 g/100 g138881-pentanol
7.8 g/100 g-2446dimethyl ethe
in ini te7846ethanol
olubilityin Wate
Boiling
Point(C)
MoleculaWeightNamet uctu al o mu la
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Ethers form hydrogen bonds with water
They are more soluble in water than
hydrocarbons of similar molar mass
18.4 Ethers18.4 Ethers
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18.4 Ethers18.4 Ethers
The effect of hydrogen bonding is
illustrated by comparing the boiling
points of ethanol and dimethyl ether
The difference is due to the polar O-Hgroup in the alcohol
This increases the attractive force
between molecules of ethanol
CH3 CH2 OH CH3 OCH3
bp-24C
Ethanol
bp C
Dim thyl ther
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18.4 Ethers18.4 Ethers
Reactions of ethers
Ethers resemble hydrocarbons in their
resistance to chemical reactions
They do not react readily with oxidising
agents or reducing agents
They are not affected by most acids or bases
at moderate temperature
Because of their good solvent properties
and general inertness to chemical
reaction, ethers are excellent solvents in
which to carry out organic reactions
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SummarySummary
Alcohols
Contain the functional group OH, the
hydroxyl group, bonded to an sp3
hybridised carbon atom
Classified as 1, 2 or 3
IUPAC names are formed by changing
the suffix of the parent alkane to ol Common names are derived by naming
the alkyl group followed by alcohol
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SummarySummary
Reactions of alcohols
Alcohols are polar compounds
Their boiling points are higher than those
of hydrocarbons of similar molar mass
Boiling points of alcohols increase with
increasing molar mass
Alcohols are more soluble in water thanhydrocarbons of similar molar mass
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SummarySummary
Ethers
Contain an oxygen atom bonded to
2 carbons not bonded to a heteroatom
They are moderately polar compounds
Their boiling points are close to those of
hydrocarbons of similar molar mass
They are more soluble in water than arehydrocarbons of similar molar mass
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