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Alcohols
IUPAC Nomenclature
of Alcohols
Nomenclature
• The longest C chain with the –OH group attached to it is
chosen as the parent group.
• The C atoms in the parent chain are numbered so that the
C atom attached with the –OH group is given the lowest
number possible.
• The position of –OH group is indicated by the number of
C atom to which it is attached.
• The substituents and their positions in the parent chain are
numbered from the C with the –OH group. The –OH group
is given higher priority compared alkyl/halogen
substituents in determining the direction of placements
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
Classes of Alcohols
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
CH3CH2CH2CH2CH2OH
primary alcohol
H
OH
secondary alcohol
CH3
CH3CCH2CH2CH3
OH
tertiary alcohol
Number of hydroxyl compound
• Hydroxy compound that have only 1 OH group:
monohydric alcohols.
– Methanol, ethanol, 2-propanol
• Have 2 –OH group: dihydric alcohols / diols.
– 1,2-ethanediol, 1,3-propanediol.
• Have 3 –OH group: trihydric alcohols / triols.
– 1,2,3-propanetriol.
Physical Properties
of Alcohols
Boiling Points
 Higher than other organic compounds with equivalent
relative molecular mass.
 Formation of hydrogen bond between –OH groups
in alcohol molecule.
 Boiling point increases as Molecular Mass of alcohol
increase since the van der Waals forces of attraction
increases with molecular size.
Boiling Points
 Boiling point of branched chain alcohol is lower than
straight chain, with same Molecular mass.
 Small surface area, hence weaker van der Waals forces.
 3° alcohol < 2° alcohol < 1° alcohol
boiling point increases
Solubility in Water
 Lower members of alcohols are soluble in water;
 Formation of H bond between water & alcohol.
 Solubility in water decreases significantly:
 Size of alkyl group, R
 R is non-polar
 Bigger influence when number of C (hence size) increases.
 Order of solubility in water;
 3° alcohol < 2° alcohol < 1° alcohol
solubility increases
• Due to stearic factor as alkyl, -R groups hinder the
formation of H-bonds between the –OH groups and
water molecules.
• Polyhydric alcohols are more soluble in water than
monohydric alcohols.
• Triol > diol > monohydric alcohols
Solubility in water decreases
this is because the more –OH groups present in a molecule,
the more hydrogen bonds are formed with water.
Reactions of
Hydroxyl Compounds
Reactions
 Divided into 2 groups:
 Type 1: Cleavage of bond between O and
H in –OH and H replaced by other groups.
 Type 2: Cleavage of bond between C and
O in –OH is replaced by other groups
through nucleophilic substitution.
Type 1 Reactions
• Hydroxyl reacts as acid.
• Occurs for both aliphatic and aromatic
alcohols
• Example reactions:
– Formation of alkoxides & phenoxides
– Formation of ester
– Oxidation of alcohol → carbonyl → carboxylic
acid
• Depends on class of alcohol
Type 2 Reactions
• Hydroxyl react as base.
• Occurs in aliphatic alcohols only.
• Example reactions:
– Rxn with hydrogen halides, phosphorus halide /
thionyl chloride.
– Dehydration → alkene / ethers.
T1:Formation of alkoxides &
Phenoxides
• Alcohol & Phenol react with
electropositive metals (Na/K) to form
salt known as alkoxides/phenoxides &
H2 gas.
Application
• Qualitative test for the presence of –OH
group.
– H2 gas released when Na?K react with
compound X. X could be alcohol/carboxylic acid
• Quantitative test for the number of –OH
groups.
• To generate H2 gas that is newly formed to
carry out reduction reactions.
T1: Esterification
• Aliphatic alcohols + carboxylic acid →
ester + water.
• Aromatic compound → no rxn.
• Acylation:
– Both aliphatic & aromatic + acyl chloride →
ester.
T1: Oxidation
• Alcohol can be oxidised to form carbonyl compound and
carboxylic acid – depend on class of alcohol.
• Involves removing 2 H atoms.
• Hot acidified potassium dichromate (VI) / potassium
manganate (VII) used.
• 1° alcohol → aldehyde → carboxylic acid.
• 2° alcohol → ketone: stable toward oxidizing agent.
• 3° alcohol → resistance toward oxidation.
T2: Rxn with PX5/PX3/SOX2/HX
• Involve fission of C-O bond in the hydroxy compound
and the –OH group is replaced by halogen in
nucleophilic substitution.
• Application:
– Conversion of alcohol → haloalkane
• To convert –OH to –X in the preparation of RX from ROH.
– Qualitative test for the presence of –OH group.
• White fumes of HCl liberated when solid PCl5 added to compound Y,
then –OH is present in comp Y.Y maybe aliphatic hydrocyl, ROH or
carboxylic acid, RCOOH.
– Quantitative test to determine number of –OH group.
• 1 mol of –OH group liberates 1 mol of hydrogen chloride gas.
• Application cont.:
– In the rxn of thionyl chloride (sulfur dichloride oxide), SOCl2
with alcohol, the chloroalkane produce can be easily isolated
as the liquid as the rest of the by-products (SO2 & HCl) are
gases.
– Alcohol react withconc. HCl / HBr to produce haloalkane.
• Lucas Reagent: mixt of conc. HCl & ZnCl2
• Distinguish class of alcohol, rate of reaction is different.
– 1° alcohol: react very slowly, no cloudiness at room temperature.
– 2° alcohol: react in 1-5min (solution turn cloudy after 5 min).
– 3° alcohol: react almost instantaneously (immediate cloudiness)
T2: Dehydration rxn
• Two types of dehydration producing diff. product at diff.
condition.
– Intramolecular elimination of water.
– Intermolecular elimination of water.
• Intramolecular elimination of water from hydroxyl group &
alpha H produce alkene.
– α-H: H attached to C adjacent to –OH group.
– By refluxing the alcohol with excess conc. H2SO4 / H3PO4 at temp.
of 170-180°C / heated with alumina.
• Intermolecular elimination of water from two alcohol
molecules to produce ether.
– Conc. H2SO4 and excess alcohol refluxed at temp. of 140°C.
Formation of Haloform
• All alcohol with structure of RCH(OH)CH3, where R is
H/alkyl/aryl group, will produce haloform when heated with
halogen & aqueous alkali.
• Haloforms: iodoform, CHI3 / chloroform, CHCl3
• Iodoform test: iodomethane formed: yellow precipitate.
– Used to identify a methyl group, -CH3 adjacent to the carbonyl group or hydroxyl
group in ethanol (1° alcohol) / 2° alcohol.
Reactions of the
Benzene Ring
in Phenol
• Since –OH group in ortho- and para- directing, phenol
undergo electrophilic substitution reactions in the 2-(ortho)
and 4-(para) positions of benzene ring under mild
conditions.
• The electrophilic substitutions ofphenol include:
– Halogenation with chlorine / bromine water.
– Nitration with conc. Nitric acid
– Friedel-Crafts alkylation & acylation.
Preparation of
Hydroxyl Compound.
Preparation: Aliphatic Alcohol
1. Hyration of alkenes.
2. Hydrolysis of haloalkanes.
3. Reaction between Grignard reagents &
carbonyl compounds.
4. Reduction of carbonyl compound.
5. Fermentation of carbohydrate.
Preparation: Phenol
1. Hydrolysis of chlorobenzene.
2. Cumene process
3. Hydroysis of diazonium salt