Alcohols

Alcohol is a compound that
has an –OH (a hydroxyl
group) bonded to a
saturated, alkane-like
carbon atom.

A. STRUCTURE OF ALCOHOLS
 The functional group of an alcohol is an – OH
(hydroxyl) group bonded to a tetrahedral
carbon atom.
a. Methanol, Lewis structure b. ball-and-stick model

B. NOMENCLATURE
1. Select the longest carbon chain that
contains the –OH group as the parent
alkane and number it from the end that
gives –OH the lower number.
In numbering the parent chain, the
location of the –OH group takes
precedence over alkyl groups, aryl
groups, and halogens.

2. Change the ending of the parent alkane
from –e to –ol, and use a number to show
the location of the –OH group.
For cyclic alcohols, numbering begins
at the carbon bearing the –OH group; this
carbon is automatically carbon -1.
Note: It’s not necessary to use the
number “1” to specify the location of
the –OH group.
3. Name and number the substituents
and list them in alphabetical order.

Classification of Alcohols
 Alcohols are classified as
primary, secondary, or
tertiary.
 Classification is determined by the number of
alkyl groups attached to the carbon bonded
to the hydroxyl.

 We classify alcohols according to the number of
carbon substituents bonded to the hydroxyl-bearing
carbon:
 PRIMARY (1˚)-alcohols with one substituent.
 SECONDARY (2˚) – alcohols with two substituents.
A primary alcohol
(one R group on –OH bearing carbon)
A secondary alcohol
(two R groups on –OH bearing carbon)

 TERTIARY (3˚)- alcohols with three substituents.
A tertiary alcohol
(three R groups on –OH bearing carbon)

 In the IUPAC system, a compound containing two
hydroxyl groups as diol, one containing three
hydroxyl groups as triol, and so on.
 In IUPAC names for diols, triols and so on, the final –e
in the name of the parent alkane is retained.
1,2-ethanediol
(ethylene glycol)
1,2,3-propanetriol
(gycerol, glycerin)

Some Common Alcohols
 Methyl Alcohol (CH3OH , Methanol)
 the simplest member of the alcohol family.
 is commonly known as wood alcohol
because it was once prepared by heating
wood in the absence of air.
 Is used industrially as starting material for
preparing formaldehyde (H2C=0) and methyl
tert-butyl ether (MTBE), an octane booster
added to gasoline.
CO(g) + 2H2(g) cu CH3OH (l)
high pressure 250 C

 Methyl alcohol is colorless, miscible
with water, and toxic to humans when
ingested or inhaled. It causes blindness in
low doses (about 15 mL for an adult) and
death in larger amounts. (100-250 mL).

 Ethyl Alcohol (CH3CH2OH , Ethanol)
 it is one of the oldest known pure
organic chemicals.
 its production by fermentation of grain and sugar goes
back many thousand years.
 sometimes called grain alcohol.
 the alcohol present in all table wines (10-13%), beers (3-
5%) and distilled liquors (35-90%).
 During fermentation, starches or complex sugars are
converted to simple sugars (C6H12O6), which are
converted to ethyl alcohol:
yeast enzymes
C6H12O6 2CH3CH2OH + 2CO2

 Isopropyl Alcohol [(CH3)2CHOH]
 often called rubbing alcohol.
 is used as a 70% mixture with water for
runbdowns because it cools the skin
through evaporation and causes pores to
close.
 It’s also used as a solvent for
medicines, as a sterilant for instruments
, and as a skin cleanser before drawing
the blood or giving injections.

 Ethylene Alcohol ( HOCH2CH2OH)
 A dialcohol, is a colorless liquid that is
miscible with water and insoluble in
nonpolar solvents.
 It’s two major uses are as antifreezer and
as a starting material for making polyester
films and fibers, such as Dacron.
 In humans, it is a central-nervous system
depressant; a ,lethal dose is about 100 mL.

 Glycerol [HOCH2CH(OH)CH2OH]
 trialcohol gylcerol is a colorless liquid that
is miscible with water.
 it is not toxic but has a sweet taste that
makes it useful in candy and prepared
foods.
 often called as glycerin.
 It is also used in cosmetics and tobacco
as a moisturizer, in plastic manufacture, in
antifreezer and shock-absorber fluids and
as a solvent.

PROPERTIES OF ALCOHOLS
 Alcohols are much more polar than
hydrocarbons because of the
electronegative oxygen atom that
withdraws electrons from the neighboring
atoms.
 Straight-chain alcohols with up to 12
carbon atoms are liquids and each boils
at a considerably higher temperature
than related alkane.

 Alcohols with two or more –OH groups
can form more than one hydrogen bond .
They are therefore higher boiling and
more water-soluble than similar alcohols
with one –OH group.

What are the characteristic
reactions of alcohols?
 A. Acidity of Alcohols
 Alcohols have about the same pKa values as
water.
 Phenols are weak acids and react with aqueous
sodium hydroxide to form water-soluble salts.
H2O
Phenol
(a water-soluble salt)

 B. Acidity-Catalyzed Dehydration Alkenes
 We can convert an alcohol to an alkene by
eliminating a molecule of water from adjacent
carbon atoms in a reaction called dehydration.
 Dehydration of alcohol is most often brought by
heating with either 85% phosphoric acid or
concentrated sulfuric acid.
 Primary alcohols –the most difficult to dehydrate –
generally require heating in concentrated sulfuric
acid ate temperatures as high as 180˚C.
 Secondary alcohols undergo acid-catalyzed
dehydration at somewhat lower temperatures.
 Tertiary alcohols generally undergo acid-
catalyzed dehydration at temperatures only
slightly above room temperature.

H2SO4
180˚C
+ H2O
Cyclohexanol Cyclohexene

1˚alcohols 2˚alcohols 3˚alcohols
 When the acid-catalyzed dehydration of
an alcohol yields isomeric alkenes, the
alkene having the greater number of alkyl
groups on the double bond generally
predominates.
EASE OF DEHYDRATION ALCOHOLS

 Hydration-dehydration reactions are
reversible.
 Alkene hydration and alcohol
dehydration are competing
reactions, and the following equilibrium
exists:
hydration
dehydration

In accordance with Le Chatelier’s principle:
 Large amounts of water (using dilute
aqueous acid) favor alcohol formation.
 Scarcity of water (using concentrated
acid) or experimental conditions where
water is removed (heating the reaction
mixture above 100˚C)favor alkene
formation.

 C. Oxidation of Primary and Secondary Alcohols
 Oxidation – is either the loss of hydrogen or the
gains of oxygen.
 A primary alcohol can be oxidized to an
aldehyde or to a carboxylic acid, depending on
the experimental conditions.

 The reagent most commonly used in the
laboratory for the oxidation of a primary
alcohol to carboxylic acid is potassium
dichromate, K2Cr2O7, dissolved in
aqueous sulfuric acid.

 Secondary alcohols may be oxidized to ketones
by using potassium dichromate as the oxidizing
agent.
 Menthol- a secondary alcohol that is present in
peppermint and other mint oils, is used in
liqueurs, cigarettes, cough
drops, perfumery, and nasal inhalers.
2-isopropyl-5-methylcyclohexanol
(methanol)
2-isopropyl-5-methylcyclohexanone
(methone)

 Tertiary alcohols resist oxidation because the
carbon bearing the –OH is bonded to three
carbon atoms and, therefore cannot form a
carbon-oxygen double bond.
K2Cr2O7
H2SO4
(NO OXIDATION)
1-methylcyclopentanol

..THANK YOU..
and God bless.. =)
PHY.SCI 2

Alcohols

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Alcohols