Alcohol

AlcoholsAlcohols

The two that are most widely used are:The two that are most widely used are:functional class nomenclaturefunctional class nomenclaturesubstitutive nomenclaturesubstitutive nomenclature

Both types can be applied to alcohols andBoth types can be applied to alcohols andalkyl halides.alkyl halides.

IUPAC NomenclatureIUPAC Nomenclature

There are several kinds of IUPAC nomenclature.There are several kinds of IUPAC nomenclature.

IUPAC NomenclatureIUPAC Nomenclature

of Alcoholsof 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

Name the alkyl group and add "alcohol" as aName the alkyl group and add "alcohol" as aseparate word.separate word.

Functional Class Nomenclature of AlcoholsFunctional Class Nomenclature of Alcohols

CHCH33CHCH22OHOH

CHCH33CHCHCHCH22CHCH22CHCH22CHCH33

OHOH

CHCH33CCHCCH22CHCH22CHCH33

OHOH

CHCH33

Name the alkyl group and add "alcohol" as aName the alkyl group and add "alcohol" as aseparate word.separate word.

Functional Class Nomenclature of AlcoholsFunctional Class Nomenclature of Alcohols

CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

Ethyl alcoholEthyl alcohol

1-Methylpentyl alcohol1-Methylpentyl alcohol

1,1-Dimethylbutyl1,1-Dimethylbutylalcoholalcohol

Name as "alkanols." Replace -e ending of alkaneName as "alkanols." Replace -e ending of alkanename by -ol.name by -ol.

Number chain in direction that gives lowest numberNumber chain in direction that gives lowest numberto the carbon that bears the —OH group.to the carbon that bears the —OH group.

Substitutive Nomenclature of AlcoholsSubstitutive Nomenclature of Alcohols

CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

Name as "alkanols." Replace -e ending of alkaneName as "alkanols." Replace -e ending of alkanename by -ol.name by -ol.

Number chain in direction that gives lowest numberNumber chain in direction that gives lowest numberto the carbon that bears the —OH group.to the carbon that bears the —OH group.


CHCH33CHCH22OHOH


OHOH


OHOH

CHCH33

EthanolEthanol

2-Hexanol2-Hexanol

2-Methyl-2-pentanol2-Methyl-2-pentanol

OHOH

CHCH33


Hydroxyl groups outrank Hydroxyl groups outrank alkyl groups when alkyl groups when it comes to numberingit comes to numberingthe chain.the chain.

Number the chain in theNumber the chain in thedirection that gives the direction that gives the lowest number to thelowest number to thecarbon that bears thecarbon that bears theOH groupOH group

CHCH33

OHOH


6-Methyl-3-heptanol6-Methyl-3-heptanol

5-Methyl-2-heptanol5-Methyl-2-heptanol

OHOH

CHCH33

CHCH33

OHOH

Classes of AlcoholsClasses of Alcohols

Alcohols and alkyl halides are classified asAlcohols and alkyl halides are classified asprimaryprimarysecondarysecondarytertiarytertiary

according to their "degree of substitution."according to their "degree of substitution."

Degree of substitution is determined by countingDegree of substitution is determined by countingthe number of carbon atoms directly attached tothe number of carbon atoms directly attached tothe carbon that bears the halogen or hydroxyl group.the carbon that bears the halogen or hydroxyl group.

ClassificationClassification

CHCH33CHCH22CHCH22CHCH22CHCH22OHOH

primary alcoholprimary alcohol

ClassificationClassification


OHOH

CHCH33

tertiary alcoholtertiary alcoholsecondary alcoholsecondary alcohol

HH

OHOH

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 Physical Properties

of Alcoholof Alcohol

Boiling Points

Higher than other organic compounds with equivalent relative molecular mass. Formation of hydrogen bond between –OH groups

in alcohol molecule.

b.p increases as Mr of alcohol increase since the van der Waals forces of attraction increases with molecular size.

Boiling Points b.p of branced chain alcohol is lower than straight

chain, with same Mr. Small surface area, hence weaker van der Waals forces. Stearic factor – lower b.p – alkyl, R hinder the formation

of H-bond.

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 Reactions of

Hydroxy CompoundHydroxy Compound

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

• Hydroxy react 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

• Hydroxy 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 Reactions of the

Benzene Ring Benzene Ring

in Phenolin 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 Preparation of

Hydroxy Compound.Hydroxy 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

Discuss Discuss

the uses of the uses of

Hydroxy CompoundHydroxy Compound

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Alcohol