ORGANIC
CHEMISTRY
CSEC
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G.Delapenha
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G.Delapenha
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ORGANIC CHEMISTRY
It is such a complex branch of chemistry because...
• CARBON is TETRAVALENT ( i.e has 4 valence electrons) and can form 4 covalent bonds.
•
Eg. methane
• CARBON ATOMS FORM STRONG COVALENT BONDS TO EACH OTHER
• THE CARBON-CARBON BONDS CAN BE SINGLE, DOUBLE OR TRIPLE
• OTHER ATOMS/GROUPS OF ATOMS CAN BE PLACED ON THE CARBON ATOMS
• GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON
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IMPORTANT!
CARBON always
forms FOUR (4)
bonds in EVERY
organic
compound,
i.e. C is
TETRAVALENT
• NOTE: the ability to form bonds between atoms of the same element is called CATENATION
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CARBON ATOMS CAN BE ARRANGED IN
STRAIGHT CHAINS
pentane
BRANCHED CHAINS
RINGS
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TYPES OF FORMULAE - 1
MOLECULAR FORMULA
The exact number of atoms of each
element present in the molecule
C4H10
EMPIRICAL FORMULA
The simplest whole number ratio
of atoms in the molecule
C2H5
FULL DISPLAYED FORMULA
Shows both the relative placing of atoms
and the number of bonds between them
there are two possible structures
H
THE EXAMPLE BEING
USED IS... BUTANE
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
C
C
C
H
H
H C H
H
CONDENSED STRUCTURAL FORMULA CH3CH2CH2CH3
The minimal detail using conventional
groups, for an unambiguous structure
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H
H
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CH3CH(CH3)CH3
H
HOMOLOGOUS SERIES
A series of compounds of similar structure in which each member differs from the next by a
common repeating unit, CH2. Series members are called homologues and...
• all share the same GENERAL FORMULA.
• formula of a homologue differs from its neighbour by CH2. (e.g. CH4, C2H6, ... etc )
• contain the same FUNCTIONAL GROUP
• have similar CHEMICAL PROPERTIES.
• show a gradual change in PHYSICAL PROPERTIES as molar mass increases.
• can usually be prepared by similar methods.
Example: ALCOHOLS - FIRST THREE MEMBERS OF THE SERIES
CH3OH
METHANOL
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C2H5OH
ETHANOL
C3H7OH
PROPAN-1-OL
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FUNCTIONAL GROUPS
A functional group is a group of atoms responsible for the
characteristic reactions of a particular compound.
Functional groups can consist of one atom, a group of atoms or
multiple bonds between carbon atoms.
HOMOLOGOUS SERIES: ALCOHOL
H H H H H
H C C C C C
OH
H H H H H
Carbon skeleton
Functional Group = HYDROXYL
The chemistry of an organic compound is determined by its FUNCTIONAL GROUP
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Eg. Alkanes, alkenes and alkynes
Eg. Alkanes
Ethane C2H6
Propane C3H8
Eg. alkenes and alkynes
ethyne
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ethene
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Naming Straight chain members of a homologous series
Eg. Alkanes ( CnH2n+2)
• are saturated hydrocarbons
• general formula CnH2n+2
• Prefix tells the number of carbon atoms
C6H14
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The Main Homologous Series
Example of
Structural Formulae
propane
C‐C
alkane
ethene
alkene
ethanol
hydroxyl
Ethanoic acid
carboxyl
n = number of carbon atoms
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Note: Every C atom ALWAYS have 4 bonds
ALKYL GROUPS
Important in the naming of branched chain
carbon compounds
• Alkanes can be described by the general formula CnH2n+2.
• An alkyl group is formed by removing one hydrogen from the
alkane chain and is described by the formula CnH2n+1.
• The removal of this hydrogen results in a stem change from
-ane to -yl.
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STRUCTURAL ISOMERISM
• Structural isomerism Is the occurrence of compounds with the same molecular formula
but different structural formulae
• Structural Isomers are compounds with the same molecular formula but different
structural formulae
 different arrangements of the carbon skeleton
 similar chemical properties
 slightly different physical properties
 more branching = lower boiling point
Example: Two structural isomers of C4H10.
2-METHYLPROPANE
branched
BUTANE
straight chain
Methyl group (CH3‐)
Higher b.pt
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Lower b.pt
CH3CH(CH3)CH3
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To avoid confusion :
• DO NOT draw bent or twisted versions of straight chain isomers
• ALWAYS draw the longest continuous chain of carbon atoms horizontally
X
X
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X
X
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X
Number of structural isomers
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Structural Isomers of Pentane (C5H12)
C5H12 has 3 structural isomers
A
B
C
4
Pentane (or n‐pentane)
3
2
1
1
2
3
CH3CH(CH3)CH2CH3
2‐methylbutane
Note:
• Isomer B and Z are the SAME isomer!
• ALWAYS number the LONGEST CONTINUOUS chain of
C atoms from the end of the chain which gives the side
group the lower number (when naming BRANCHED
CHAIN ISOMERS)
• Separate numbers(or locants) from side groups by a
hyphen
• Separate numbers with commas
• Use di, tri, tetra, penta, hexa, … etc for multiple
identical
side groups.
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2,2‐dimethylpropane
Z
1
2
3
4
CH3CH(CH3)CH2CH3
2‐methylbutane
Question:
a) How many isomers of C6H14 are there?
b) Draw ALL structural isomers of C6H14
c) Write the condensed structural formula of each
structural isomers give each its systematic(or IUPAC)
name
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• Petroleum (or crude oil - a fossil fuel) is a usually black or dark brown, but can also be yellowish,
reddish, tan, or even greenish complex mixture of hydrocarbons that occur in the Earth in liquid,
gaseous, or solid form.
• Like coal and natural gas, petroleum was formed from the remains of ancient marine organisms,
such as plants, algae, and bacteria.
• Natural gas is colourless highly flammable gaseous hydrocarbon mixture consisting primarily
of methane and ethane and small quantities of propane and butane
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Fractional Distillation of Crude Oil
•
After removing impurities,
the various components or
fractions are separated by
fractional distillation in a
fractionating tower in an
oil refinery.
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Refinery gas
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USES OF PETROLEUM FRACTIONS
Petrol(or gasoline)
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• Liquefied Natural Gas (LNG) is natural gas (predominantly methane,
CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid
form for ease and safety of non-pressurized storage or transport.
• Liquefied Petroleum Gas: a compressed gas that consists of
flammable hydrocarbons (such as propane and butane) and is used
especially as fuel
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NAMING ALKENES
Length
In alkenes the principal chain is not always the longest chain
It must contain the double bond
the name ends in -ENE
Position
Count from one end as with alkanes.
Indicated by the lower numbered carbon atom on one end of the C=C bond
5
4
3
2
1
CH3CH2CH=CHCH3
Side-chain
is pent-2-ene
Similar to alkanes
position is based on the number allocated to the double bond
1
2
3
4
1
CH2 = C(CH3)CH2CH3
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(NOT pent-3-ene)
2-methylbut-1-ene
2
3
4
CH2 = CHCH(CH3)CH3
3-methylbut-1-ene
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STRUCTURAL ISOMERISM IN ALKENES
•
•
•
•
molecule has the same carbon skeleton
molecule has the same functional group... BUT
the functional group is in a different position
have similar chemical properties / different physical properties
POSITION OF A DOUBLE BOND IN ALKENES
Example 1
1
2
CH3CH
2CH2CH=CH2
PENT-1-ENE
double bond between
carbons 1 and 2
2
3
CH3CH
2CH=CHCH3
PENT-2-ENE
double bond between
carbons 2 and 3
There are no other isomers with five C’s in the longest chain but there are three
other structural isomers with a chain of four carbons plus one in a branch.
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CHEMICAL REACTIONS
OF ALKANES
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CHEMICAL PROPERTIES OF ALKANES
• UNREACTIVE;
• have relatively strong, NON-POLAR, SINGLE covalent
bonds
• Unreactive to:
o Strong acids
o Strong bases/alkalis
o Strong oxidizing agents/reducing agents
• Alkanes can however, undergo the following reactions:
1) Combustion(a type of oxidation)
2) Free Radical substitution
3) Cracking
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Halogenation of Alkanes
If a mixture of methane and chlorine is kept in the dark at room
temperature, no change occurs
If the mixture is heated or exposed to visible or ultraviolet light,
reaction begins at once with the evolution of heat
Substitution: a reaction in which an atom or group of atoms is
replaced by another atom or group of atoms
CHLORINATION OF METHANE
Reagents
chlorine and methane react in a CHAIN REACTION in presence of UV light
Conditions
UV light or sunlight - heat is an alternative energy source
Equation(s)
step 1 CH4(g) + Cl2(g)
——> HCl(g)
+ CH3Cl(g)
chloromethane
step 2 CH3Cl(g) + Cl2(g) ——> HCl(g) + CH2Cl2(l) dichloromethane
step 3 CH2Cl2(l) + Cl2(g) ——> HCl(g) + CHCl3(l) trichloromethane
step 4 CHCl3(l) + Cl2(g) ——> HCl(g)
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+ CCl4(l)
tetrachloromethane
CRACKING
• Involves the breaking of long chain hydrocarbons by
heat/catalyst to form shorter chained more useful
hydrocarbons.
• Converts heavy fractions into higher value products
• Used to produce gasoline
TWO (2) types:
o THERMAL cracking
o CATALYTIC cracking
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Thermal cracking of Alkanes
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Cracking
Example
heptane
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pentane
At least 1 alkene and 1
alkane is formed during
cracking of a hydrocarbon
chain.
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Black River
High School
Reactions of Alkenes
Alkenes
Examples
1
3
1
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4
2
2
but-1-ene OR 1-butene
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3
but-2-ene OR 2-butene
4
ADDITION OF BROMINE
Reagent:
Bromine. (dissolved in tetrachloromethane, CCl4 or hexane)
Condition: Room temperature.
Equation: C2H4(g) + Br2(l) ——> CH2BrCH2Br(l) 1,2 - dibromoethane
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ADDITION OF BROMINE
TEST FOR UNSATURATION
The addition of bromine dissolved in tetrachloromethane (CCl4) or water (known as bromine
water) is used as a test for unsaturation. If the reddish-brown colour is removed from the
bromine solution, the substance possesses a C=C bond.
A Place a solution of
bromine in a test tube
Add the hydrocarbon to
B be tested and shake
If the brown colour
C disappears then the
hydrocarbon is an
alkene
A
B
C
Because the bromine adds to the alkene, it no longer exists as molecular bromine and
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typical red-brown colour disappears G.Delapenha
TEST FOR UNSATURATION
• Alkene can also be tested for using acidified
potassium manganate(VII) solution.
• Colour change: purple to colourless
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ADDITION OF HYDROGEN BROMIDE
Condition
Equation
Room temperature.
C2H4(g) + HBr(g)
———>
C2H5Br(l)
bromoethane
ethene
bromoethane
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Hydration of Ethene (addition of water)
Dilute sulfuric acid
(a catalyst)
heat
Ethene or
i.e. steam
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Oxidation of Alkenes with Cold Acidified potassium manganate(VII) solution
• The purple solution becomes colourless
ethene
ethane-1,2-diol
Other alkenes react in just the same way.
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HYDROGENATION
Conditions nickel catalyst - finely divided/150C/500kPa
Equation
C2H4(g) +
H2(g)
———>
C2H6(g)
ethane
Ni
ethene
ethane
Used in margarine manufacture
o Vegetable oils consist mostly of unsaturated hydrocarbon chains.
o They are hardened by reducing the number of double bonds.
o Hydrogenation of fats also produces trans-fats which are harmful to health
o They
contribute to heart and circulatory
disease.
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Hydration of Ethene
•
ethene reacts with water, in the presence of steam, to form ethanol:
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Reactions of Alcohols
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Presenter
Gregory Delapenha
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ALCOHOLS
Functional Group: the hydroxyl (- OH) group
Aliphatic • general formula CnH2n+1OH - provided there are no rings
or R-O-H where R represents an alkyl group
• the hydroxyl (- OH) group replaces an H in a basic hydrocarbon skeleton
Methanol (n = 1)
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Ethanol (n = 2)
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Propan‐1‐ol (n = 3)
ALCOHOLS
• Functional Group: the hydroxyl (- OH) group
•
general formula: CnH2n+1OH or R-O-H (where R represents an alkyl group)
• the hydroxyl (- OH) group replaces an H in a basic hydrocarbon skeleton
Condensed structural formula
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Nomenclature of Alcohols
Alcohols are named according to standard IUPAC rules
1) select the longest chain of C atoms containing the O-H group;
2) remove the e and add ol after the basic name
3) number the chain starting from the end nearer the O-H group
4) the number is placed after the an and before the ol ... e.g butan-2-ol
5) as in alkanes, prefix with alkyl substituents
6) side chain positions are based on the number allocated to the O-H group
e.g.
Structural isomers of C3H7OH
Propan‐1‐ol (or 1‐propanol)
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Propan‐2‐ol (or 2‐propanol)
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STRUCTURAL ISOMERISM IN ALCOHOLS
Different structures are possible due to...
Different positions for the OH group and
Branching of the carbon chain


butan-1-ol
4
3 2
2-methylpropan-2-ol
butan-2-ol
1
1
2
3
4
1
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2
3
Reaction of ethanol with sodium
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Example:
Dehydration of Ethanol
H2 SO 4
CH 3 CH 2 OH
CH 2 = CH 2
Reflux at 180°C
+
H2 O
Reflux is a distillation
technique involving
the condensation of vapors
and the return of this
condensate to the system
from which it originated.
Reagent/catalyst: conc.
sulphuric acid (H2SO4) or conc.
phosphoric acid (H3PO4)
Alternative
Method
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Pass vapour over a heated alumina (aluminium oxide) catalyst
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OXIDATION OF ETHANOL
• When ethanol is heated with acidified potassium manganate(VII) or
acidified potassium dichromate (VI), the ethanol is oxidized to ethanoic
acid.
C2H5OH(l) + 2[O]
CH3COOH (aq) + H2O (l)
ethanol
a reducing agent
ethanoic acid
from oxidizing agent
OBSERVATION: acidified potassium manganate(VII) color changed from purple to colourless
Or acidified potassium dichromate (VI changed from orange to green
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Breathalyser Test
•
A driver suspected of driving under the influence (dui) of alcohol is given a
device containing orange crystals of potassium dichromate lightly soaked in
dilute sulphuric acid.
• The driver is then asked to exhale into the device. The alcohol vapour is
oxidised by the crystals which are at the same time reduced to the green
Cr3+ ion.
• The intensity of the green colour is calibrated to alcohol concentration in the
blood which is shown as a digital readout.
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Producing Ethanol by Fermentation
• Ethanol is the alcohol found in beer, wine and other alcoholic drinks. It is also used as a fuel for vehicles,
either on its own or mixed with petrol. Ethanol can be produced by fermentation and concentrated
using fractional distillation.
• Fermentation is an anaerobic process( i.e. in absence of oxygen:
zymase
• Yeast, a type of single-celled fungus, provides the enzymes (called zymase) needed for
fermentation. If the yeast cells become too cold, fermentation happens very slowly, or may not
happen at all. If the yeast cells become too hot, their enzymes become denatured and fermentation
stops.
• The typical conditions needed for fermentation include:
o sugars dissolved in water, and mixed with yeast
o an air lock to allow carbon dioxide out, while stopping air getting in
o warm temperature, 25-35°C
• The yeast dies when the ethanol concentration reaches about 15%. Fermentation is a slow reaction and
takes several days or weeks to finish.
• If air is present, the oxygen causes the ethanol to oxidize to ethanoic acid, so the drink tastes of
vinegar.
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Reactions of Alkanoic acids (or Carboxylic Acids)
Colloquially called organic acids
Structure
Alkanoic acids are weak organic acids
The functional group is a carboxyl group (a carbonyl + hydroxyl)
:
O:
:
C
:O
COOH
H
CO 2 H
17
17-65
Naming Alkanoic acids
IUPAC names: drop the -e from the parent alkane and add the
suffix -oic acid
Fully Displayed Structural formula of 1st four alkanoic acids
Methanoic acid
ethanoic acid
propanoic acid
butanoic acid
Physical Properties
• water solubility decreases as the relative size of the hydrophobic portion of
the molecule increases
Polar carboxyl
group
Hydrophilic
(water-loving)
Non-polar hydrocarbon chain
Hydrophobic (water-hating)
Reaction of Carboxylic Acid with Bases
ACID + BASE
SALT + WATER
Carboxylic acids, react with NaOH, KOH, and other strong bases to
give water-soluble salts
Ethanoic acid
Sodium ethanoate
Reaction of Carboxylic Acid with Metals
ACID + METAL
SALT + HYDROGEN
Carboxylic acids, react with reactive metals such as Na, K, Ca, to
give water-soluble salts
2CH3COOH(aq) + 2Na(s)
ethanoic acid
Mg(s)
magnesium
sodium
+ 2HCOOH(aq)
methanoic acid
or formic acid
2CH3COONa(aq) + H2(g)
sodium ethanoate
hydrogen
(HCOO)2Mg(aq)
magnesium methanoate
or magnesium formate
+
H2(g)
Reaction of Carboxylic Acids with Carbonates/ Bicarbonates
Carboxylic acids react with sodium carbonate and sodium
bicarbonate to form water-soluble salts and carbonic acid
• carbonic acid, in turn, breaks down to carbon dioxide and water
ACID + CARBONATE
SALT + CARBON DIOXIDE + WATER
2CH3COOH(aq) + Na2CO3(s)
2CH3COONa(aq) + CO2(g) + H2O(l)
ethanoic acid
sodium carbonate
sodium ethanoate
ethanoic acid
sodium bicarbonate
sodium ethanoate
ESTERIFICATION
A condensation reaction between a CARBOXYLIC ACID and an ALCOHOL and catalyzed by conc.
Sulfuric acid
conc. H2SO4
carboxylic acid + alcohol
ester + water
reflux
e.g.
CH3CH2OH(l) + CH3COOH(l)
ethanol
ethanoic acid
CH3COOC2H5(l) + H2O(l)
ethyl ethanoate
Note:
 Concentrated H2SO4 is a dehydrating agent - it removes water causing the
equilibrium to move to the right and increases the yield
 Forward reaction is a condensation reaction
 Backward reaction is hydrolysis
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Nomenclature (Naming) of esters
Named from the alcohol and carboxylic acid which made them...
CH3COOH +
ethanoic acid
CH3OH
CH3COOCH3 + H2O
methanol
METHYL ETHANOATE
Fully displayed formula
METHYL ETHANOATE
from methanol
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Names of esters end in –oate.
Naming
Named after alcohol & carboxylic acid from which
they are derived.
ethyl ethanoate
this part comes from the
alcohol & is named after it
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this part from the acid
and is named after it
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Structural formulae
Although the previous structural formula are the clearest
way of showing esters, they can draw out in a
shortened form.
Or…
O
CH3 C
O
CH2
CH3
ethyl ethanoate
 Identify the group attached to the C=O – this is from
the acid
 The group attached to the –O- is from the alcohol.
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Uses of Esters
 a constituent of perfumes, essential oils, food flavourings, cosmetics,
 organic solvents
 Natural esters are found in pheromones
 Naturally occurring fats and oils are fatty acid esters of glycerol
 Polyesters are used to make plastics
 used to make surfactants E.g. soap, detergents
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Reactions of Esters
Esters have fruity sweet-smelling fragrances.
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Wait! What’s that smell?
ester
ethyl methanoate
3-methylbutyl ethanoate
ethyl 2-methylbutanoate
phenylmethyl ethanoate
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fragrance
raspberries
pears
apples
jasmine
• Esters have strong, sweet smells.
• Their bouquet is often floral or fruity.
• This means they are used in food flavourings &
perfumes.
• Also, very good at dissolving organic compounds so
often used as solvents. G.Delapenha
Ester hydrolysis
Breakdown of an ester by water.
Process sped up by catalysis
Can use an acid to catalyse (H2SO4)
Alkali catalysts (e.g. sodium hydroxide) can also
be used but instead of producing carboxylic acid
a carboxylate salt is formed.
Alkaline hydrolysis goes to completion & hence is
usually preferred.
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Hydrolysis of Esters - Reaction with H2O
• Esters are hydrolyzed only slowly, even in boiling water
• hydrolysis becomes more rapid if they are heated with either aqueous acid or
base
Acid Catalyzed Hydrolysis of Esters
 Hydrolysis in aqueous acid is the reverse of esterification
 The reaction is catalysed by dilute acid, and so the ester is heated under
reflux with a dilute acid like dilute hydrochloric acid or dilute sulphuric
acid.
dil. acid
reflux
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Base Catalyzed Hydrolysis of Esters
 Hydrolysis of an ester in aqueous base is often called
saponification
 The ester is heated under reflux with a aqueous alkali like sodium
hydroxide solution.
Advantages
 The reactions are one-way rather than reversible, and
 the products are easier to separate.
Example:
CH3COO-Na+ (aq) + CH3CH2CH2OH (aq)
propyl
ethanoate
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base
sodium ethanoate
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propan-1-ol
Saponification
• a process by which triglycerides are reacted with sodium or potassium hydroxide to produce
glycerol and a fatty acid salt, called 'soap'.
• Soaps are the sodium or potassium salts of long chain carboxylic acids.
• ‘soft’ toilet soap is generally made by the base hydrolysis of the esters in
vegetable oils
• An alcohol is also produced - in this case, the more complicated alcohol, propane-1,2,3triol (glycerol).
Generally,
heat
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Soapy And Soapless Detergents
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Disadvantages
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POLYMERS
• A POLYMER is a large molecule, or macromolecule, built up
from many(> 50) smaller units (called monomers).
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POLYMERS
2 main types
ADDITION POLYMERS
CONDENSATION POLYMERS
(all synthetic)
NATURAL
none
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SYNTHETIC (or MAN-MADE)
NATURAL
Polyalkenes
Polyamides
Polythene
Polypropene
PVC
Polystyrene
PTFE
• Protein (Hair, Wool,
Silk)
Polysaccharides
• Starch,
• Cellulose ( Cotton)
•
•
•
•
•
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SYNTHETIC (or MAN-MADE)
Polyesters
• Terylene or
Dacron or PET
Polyamides
• nylon 6,6
POLYMERISATION
• A process in which small molecules called monomers join together into
large molecules consisting of repeating units.
2 basic types
ADDITION POLYMERISATION
•
•
•
all the atoms in the monomer are used to form the polymer
The monomer must be saturated (eg ethene)
Empirical formulae of monomer and polymer are the SAME
CONDENSATION POLYMERISATION
•
•
•
monomers join up with the expulsion of small molecules
not all the original atoms are present in the polymer
At Least 2 functional groups must be on the monomer
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POLYMERISATION OF ALKENES
ADDITION POLYMERISATION
an alkene undergoes an addition reaction with itself
• all the atoms in the original alkenes are used to form the polymer
• long hydrocarbon chains are formed
(repeat unit)
n represents a large number
The equation shows the original monomer and the repeating unit in the polymer
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POLYMERISATION OF ALKENES
OTHER EXAMPLES OF ADDITION POLYMERISATION
(or vinylchloride)
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(or polyvinylchloride)
POLYMERISATION OF ALKENES
polymer
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SPOTTING THE MONOMER
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monomer
CONDENSATION POLYMERS
• monomers join up the with expulsion of small molecules
• not all the original atoms are present in the polymer
POLYMER
MONOMERS
polyamides(nylon)
protein
polyesters(terylene or PET)
polysaccharides
dicarboxylic acids and diamines
amino acids
dicarboxylic acids and diols
Simple sugars
ESTER LINK
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POLYESTERS - TERYLENE
Contain the ESTER linkage:
terephthalic acid
‘Terylene’, ‘Dacron’, PET
Uses: fabrics , bottles,
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ethane-1,2-diol
POLYAMIDES - NYLON-6,6 ( a synthetic or man-made polyamide)
• contain the amide linkage
+
n
+
Repeat unit
Nylon 6,6
Amide linkage
Uses: fishing lines, stockings, car parts, fabrics
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2n H2O
PROTEINS ( are natural polyamides)
• polypeptides with large relative molecular masses (>10000)
• chains can be lined up with each other
Protein contains
the AMIDE LINK
Uses: building block of muscles, skin, hair, wool, silk
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Polysaccharides
• Polysaccharides are natural polymers formed by linking monomers known
as rnonosaccharides together.
• Examples of monosaccharides include glucose, fructose and galactose.
These are all isomers with the molecular formula C6H12O6
• Contain the ether linkage, that is, the C-O-C linkage
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Formation of a Disaccharide and a polysaccharide
Eg. sucrose
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Formation of Starch
• Starch is a polysaccharide formed when glucose undergoes condensation
polymerisation.
n
n
n
If we think of two of the -OH groups of a glucose molecule as being functional
groups, then we can represent the glucose molecule as H-O-X-O-H, where
X represents the rest of the glucose molecule, i.e. C6H10O4
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