PRESENTATION NAME

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ORGANIC CHEMISTRY CHM 207
CHAPTER 3 ALKENES
NOR AKMALAZURA JANI
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SUBTOPICS

• Naming alkenes and cycloalkenes.
• Physical properties of alkenes
• i) boiling points and densities
• ii)polarity
• Preparation of alkenes
• i) dehydration of alcohols
• ii) dehydrohalogenation of haloalkanes

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• Reactions of alkenes
• i) Addition reaction
• a) Catalytic hydrogenation
• b) Addition of halogens
• - In inert solvent
• - In water / aqueous medium
• c) Addition of hydrogen halides
• d) Addition reaction with concentrated
  sulfuric acid hydration of
• alkenes
• e) Addition reaction with acidified water
  (H3O) hydration of alkenes
• ii) Combustion of alkenes
• iii) Oxidation

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• Unsaturation tests of alkenes
• i) Reactions of alkenes with KMnO4
• ii) Reactions of alkenes with bromine.
• Uses of alkenes
• i) PE
• ii) PVC
• iii) ethanol

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ALKENES

• Also called olefins
• Contain at least one carbon-carbon double bond
  (CC)
• General formula, CnH2n (n2,3,)
• Classified as unsaturated hydrocarbons (compound
  with double or triple carbon-carbon bonds that
  enable them to add hydrogen atoms.
• sp2-hybridized
• For example
• C2H4 - ethylene

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Naming Alkenes
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IUPAC RULES

• RULE 1. Select the longest continuous carbon
  chain that contains a double bond.

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• RULE 2. Name this compound as you would an
  alkane, but change ane to ene for an alkene.

This is the longest continuous chain. Select it
as the parent compound.
Name the parent compound octene.
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RULE 3. Number the carbon chain of the parent
compound starting with the end nearer to the
double bond. Use the smaller of the two numbers
on the double-bonded carbon to indicate the
position of the double bond. Place this number
in front of the alkene name.
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IUPAC RULES
This end of the chain is closest to the double
bond. Begin numbering here.
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IUPAC RULES
The name of the parent compound is 1-octene.
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3
2
1
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6
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RULE 4. Branched chains and other groups are
treated as in naming alkanes. Name the
substituent group, and designate its position on
the parent chain with a number.
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IUPAC RULES
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NEW IUPAC NAMES

• Placing numbers (location of double bond) before
  the part of the name ene.
• Example

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• A compound with more than one double bond.
• Two double bond diene
• Three double bond triene
• Four double bond tetraene
• Numbers are used to specify the locations of
  the double bonds.

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ALKENES AS SUBSTITUENTS

• Alkenes names as substituents are called alkenyl
  groups.
• Can be named systematically as ethenyl, propenyl,
  etc. or by common names such as vinyl, ally,
  methylene and phenyl groups.

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CYCLOALKENES

• Contains CC in the ring

• Nomenclature of cycloalkenes
• Similar to that alkenes
• Number the cycloalkane so that the double bond is
  between C1 and C2 and so that the first
  substituent has as low a number as possible.
• Double bond always between C1 and C2.

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NOMENCLATURE OF cis-trans ISOMERS

• cis two particular atoms (or groups of atoms)
  are adjacent to each other
• trans the two atoms (or groups of atoms) are
  across from each other

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PHYSICAL PROPERTIES OF ALKENES

• Boiling points and densities
• - Most physical properties of alkenes are
  similar to those alkanes.
• - Example the boiling points of 1-butene,
  cis-2-butene, trans-2-butene and n-butane are
  close to 0oC.
• - Densities of alkenes around 0.6 or 0.7 g/cm3.
• - Boiling points of alkenes increase smoothly
  with molecular weight.
• - Increased branching leads to greater
  volatility and lower boiling points.

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• Polarity
• - relatively nonpolar.
• - insoluble in water but soluble in non-polar
  solvents such as hexane, gasoline, halogenated
  solvents and ethers.
• - slightly more polar than alkanes because
• i) electrons in the pi bond is more polarizable
  (contributing to instantaneous dipole moments).
• ii) the vinylic bonds tend to be slightly polar
  (contributing to a permanent dipole moment).

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• Alkyl groups are electron donating toward double
  bond, helping to stabilize it. This donating
  slightly polarizes the vinylic bond, with small
  partial positive charge on the alkyl group and a
  small negative charge on the double bond carbon
  atom.
• For example, propene has a small dipole moment of
  0.35 D.

Vinylic bonds

• propene, µ 0.35 D

Vector sum propene, µ 0.33 D cis-2-butene,
bp 4oC
Vector sum 0 propene, µ 0 trans-2-butene, bp
1oC
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• In a cis-disubstituted alkene, the vector sum of
  the two dipole moments is directed perpendicular
  to the double bond.
• In a trans-disubstituted alkene, the two dipole
  moments tend to cancel out. If an alkene is
  symmetrically trans-disubstituted, the dipole
  moment is zero.

Vector sum propene, µ 0.33 D cis-2-butene,
bp 4oC
Vector sum 0 propene, µ 0 trans-2-butene, bp
1oC
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• Cis- and trans-2-butene have similar van der
  Waals attractions, but only cis isomer has
  dipole-dipole attractions.
• Because of its increased intermolecular
  attractions, cis-2-butene must be heated to a
  slightly higher temperature (4oC versus 1oC)
  before it begins to boil.

Vector sum propene, µ 0.33 D cis-2-butene,
bp 4oC
Vector sum 0 propene, µ 0 trans-2-butene, bp
1oC
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PREPARATION OF ALKENES

• Dehydration of alcohols
• Dehydrohalogenation of haloalkanes

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PREPARATION OF ALKENES

• Alkenes can be prepared in the following ways
• i) Dehydration of alcohols

conc. H2SO4
R-CH2-CH2-OH
R-CHCH2 H2O
ii) Dehydrohalogenation of haloalkanes
NaOH/ethanol
R-CH2-CH2-X
R-CHCH2 HX
reflux
NaOH can be replaced by KOH
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• Saytzeff rule
• - A reaction that produces an alkene would
  favour the formation of an alkene that has the
  greatest number of substituents attached to the
  CC group.

Dehydration of alcohols
Dehydrohalogenation of haloalkanes
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REACTIVITY OF ALKENES

• More reactive than alkanes because
• A carbon-carbon double bond consists of a s and a
  p bond. It is easy to break the p bond while the
  s bond remains intact.
• The p electrons in the double bond act as a
  source of electrons (Lewis base). Alkenes are
  reactive towards electrophiles which are
  attracted to the negative charge of the p
  electrons.
• p bond will broken, each carbon atom becomes an
  active site which can form a new covalent bond
  with another atom. One p bond is converted into 2
  s bonds.

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REACTION OF ALKENES

• i) Addition reaction
• a) Catalytic hydrogenation
• b) Addition of halogens
• - In inert solvent
• - In water / aqueous medium
• c) Addition of hydrogen halides
• d) Addition reaction with concentrated
  sulfuric acid hydration of
• alkenes
• e) Addition reaction with acidified water
  (H3O) hydration of alkenes
• ii) Combustion of alkenes
• iii) Oxidation
• a) epoxidation
• b)hydroxylation

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REACTIONS OF ALKENES

• Catalytic hydrogenation
• - hydrogenation addition of hydrogen to a
  double bond and triple bond to yield saturated
  product.
• - alkenes will combine with hydrogen in the
  present to catalyst to form alkanes.

• Plantinum (Pt) and palladium (Pd) Catalysts
• Pt and Pd temperature 25-90oC
• Nickel can also used as a catalyst, but a higher
  temperature of 140oC 200oC is needed.

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• Addition of halogens
• i) In inert solvent
• - alkenes react with halogens at room
  temperature and in dark.
• - the halogens is usually dissolved in an inert
  solvent such as dichloromethane (CH2Cl2) and
  tetrachloromethane (CCl4).
• - Iodine will not react with alkenes because it
  is less reactive than chlorine and bromine.
• - Fluorine is very reactive. The reaction will
  produced explosion.

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EXAMPLES
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• Addition of halogens
• ii) In water / aqueous medium
• - chlorine dissolves in water to form HCl and
  chloric (l) acid
• (HOCl).
• Cl2 (aq) H2O(l) HCl(aq) HOCl
  (aq)
• - same as bromine
• Br2 (aq) H2O(l) HBr(aq) HOBr(aq)
• Reaction of alkenes with halogens in water
  (eg. chlorine water and bromine water) produced
  halohydrins (an alcohol with a halogen on the
  adjacent carbon atom).

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• EXAMPLES

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• Addition of hydrogen halides
• - Addition reaction with electrophilic reagents.
• - Alkenes react with hydrogen halides (in
  gaseous state or in aqueous solution) to form
  addition products.
• - The hydrogen and halogen atoms add across the
  double bond to form haloalkanes (alkyl halides).
• - General equation

• Reactivity of hydrogen halides HF lt HCl lt HBr lt
  HI

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Reaction with HCl needs a catalyst such as AlCl3
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MARKOVNIKOVS RULE

• There are 2 possible products when hydrogen
  halides react with an unsymmetrical alkene.
• It is because hydrogen halide molecule can add to
  the CC bond in two different ways.

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• Markovnikovs rules
• - the addition of HX to an unsymmetrical alkene,
  the hydrogen atom attaches itself to the carbon
  atom (of the double bond) with the larger number
  of hydrogen atoms.

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Mechanism of electrophilic addition reactions -
CC electron rich part of the alkene molecule -
Electrophiles electron-seeking Step 1
Formation of carbocation. Attack of the pi bond
on the electrophile to form carbocation.
Step 2 Rapid reaction with a negative ion.
The negative ion (Y-) acts as nucleophile and
attacks the positively charged carbon atom to
give product of the addition reaction.
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ADDITION OF HYDROGEN HALIDES TO UNSYMMETRICAL
ALKENES AND MARKOVNIKOVS RULE
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• Addition reaction with concentrated sulfuric
  acid hydration of alkenes
• - the alkene is absorbed slowly when it passed
  through concentrated sulfuric acid in the cold
  (0-15oC).
• - involves the addition of H atom and HSO4 group
  across the carbon-carbon double bond.
• - follows Markovnikovs rule.

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• Addition reaction with acidified water (H3O)
  hydration of alkenes
• Hydration The addition of H atoms and OH groups
  from water molecules to a multiple bond.
• Reverse of the dehydration reaction.
• Direct hydration of ethene
• - passing a mixture of ethene and steam over
  phosphoric (v) acid (H3PO4) absorbed on silica
  pellets at 300oC and a pressure of 60
  atmospheres.
• - H3PO4 is a catalyst.

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• Markovnikovs rule is apply to the addition of a
  water molecule across the double bond of an
  unsymmetrical alkene.
• For examples

H catalyst
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H catalyst
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ANTI-MARKOVNIKOVS RULE FREE RADICAL ADDITION OF
HYDROGEN BROMIDE

• When HBr is added to an alkene in the absence of
  peroxides it obey Markovnikovs rule.
• When HBr (not HCl or HI) reacts with
  unsymmetrical alkene in the presence of peroxides
  (compounds containing the O-O group) or oxygen,
  HBr adds in the opposite direction to that
  predicted by Markovnikovs rule.
• The product between propene and HBr under these
  conditions is 1-bromopropane and not
  2-bromopropane.

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• Anti-Markovnikovs addition
• - peroxide-catalysed addition of HBr occurs
  through a free radical addition rather than a
  polar electrophilic addition.
• - also observed for the reaction between HBr and
  many different alkenes.
• - not observed with HF, HCl or HI.

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Formation of anti-Markovnikov alcohol

• Alkenes goes to hydroboration reaction to form
  anti-Markovnikov alcohol.

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• Combustion of alkenes
• The alkenes are highly flammable and burn readily
  in air, forming carbon dioxide and water.
• For example, ethene burns as follows
• C2H4 3O2 ? 2CO2 2H2O

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OXIDATION

• Oxidation reactions that form carbon-oxygen
  bonds.
• Oxidation reaction of alkenes
• i) epoxidation
• ii)hydroxylation
• iii)Ozonolysis

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EPOXIDATION OF ALKENES

• Epoxide / oxirane a three-membered cyclic ether.

• Examples of epoxidizing reagent

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Examples
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HYDROXYLATION OF ALKENES

• Hydroxylation
• - Converting an alkene to a glycol requires
  adding a hydroxyl group to each end of the double
  bond.
• Hydroxylation reagents
• i) Osmium tetroxide (OsO4)
• ii)Potassium permanganate (KMnO4)

glycol
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Also known as Baeyers test
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OZONOLYSIS OF ALKENES

• Ozonolysis
• - The reaction of alkenes with ozone (O3) to
  form an ozonide, followed by hydrolysis of the
  ozonide to produce aldehydes and /or ketone.
• - Widely used to determine the position of the
  carbon-carbon double bond.
• - Ozonolysis is milder and both ketone and
  aldehydes can be recovered without further
  oxidation.

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EXAMPLES
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REACTIONS OF ALKENES WITH HOT, ACIDIFIED KMnO4
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POLYMERIZATION OF ALKENES

• Polymer A large molecule composed of many
  smaller repeating units (the monomers) bonded
  together.
• Alkenes serves as monomers for some of the most
  common polymers such as polyethylene
  (polyethene), polypropylene, polystyrene,
  poly(vinyl chloride) and etc.
• Undergo addition polymerization /chain-growth
  polymer
• - a polymer that results from the rapid addition
  of one molecule at a time to a growing polymer
  chain, usually with a reactive intermediate
  (cation, radical or anion) at the growing end of
  the chain.

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repeating unit
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SOME OF THE MOST IMPORTANT ADDITION POLYMERS
POLYMER POLYMER USES MONOMER FORMULA POLYMER REPEATING UNIT
Polyethylene Bottles, bags, films
Polypropylene Plastics, olefin fibers
Polystyrene Plastics, foam insulation
Poly(isobutylene) Specialized rubbers
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UNSATURATION TESTS FOR ALKENES

• Reactions of alkenes with KMnO4
• - KMnO4 is a strong oxidising agent.
• - alkenes undergo oxidation reactions with KMnO4
  solution under two conditions
• a) Mild oxidation conditions using cold, dilute,
  alkaline KMnO4 (Baeyers test).
• b) Vigorous oxidation conditions using hot,
  acidified KMnO4.

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• Reaction of alkenes with cold, dilute, alkaline
  KMnO4 (Baeyers test)
• - the purple colour of KMnO4 solution disappears
  and a cloudy brown colour appears caused by the
  precipitation of manganese (IV) oxide, MnO2.
• - test for carbon-carbon double or triple bonds.
• - a diol is formed (containing two hydroxyl
  groups on adjacent carbon atoms).

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• 2) Reactions of alkenes with bromine
• - A solution of bromine in inert solvent (CH2CI2
  or CCI4) and dilute bromine water are yellow in
  colour.
• - The solution is decolorised when added to
  alkenes or organic compounds containing CC bonds.

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DETERMINATION OF THE POSITION OF THE DOUBLE BOND

• a) Ozonolysis of alkenes
• - For example, ozonolysis of an alkene produces
  methanal and propanone.

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• b) Reaction of alkenes with hot, acidified KMnO4
• - by using hot, acidified KMnO4, the diol
  obtained is oxidised further.
• - cleavage of carbon-carbon bonds occurs and the
  final products are ketones, carboxylic acids or
  CO2.

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• Example
• An alkene with the molecular formula C6H12 is
  oxidised with hot KMnO4 solution. The carboxylic
  acids, butanoic acid (CH3CH2CH2COOH) and ethanoic
  acid (CH3COOH), are produced. Identify the
  structural formula of the alkene.

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USES OF ALKENES

• Ethylene and propylene are the largest-volume
  industrial organic chemicals.
• Used to synthesis a wide variety of useful
  compounds.

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POLYETHENE (PE)

• The most popular plastic.
• Uses
• i) Grocery bags
• ii)Shampoo bottles
• iii)Children's toy
• iv)Bullet proof vests
• v)Film wrapping
• vi)Kitchenware

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POLYVINYL CHLORIDE (PVC)

• USES OF PVC
• Clothing
• - PVC fabric has a sheen to it and is
  waterproof.
• - coats, shoes, jackets, aprons and bags.
• As the insulation on electric wires.
• Producing pipes for various municipal and
  industrial applications. For examples, for
  drinking water distribution and wastewater mains.
• As a composite for the production of accessories
  or housings for portable electronics.
• uPVC or Rigid PVC is used in the building
  industry as a low-maintenance material.
• Ceiling tiles.

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USES OF ETHANOL

• Motor fuel and fuel additive.
• As a fuel to power Direct-ethanol fuel cells
  (DEFC) in order to produce electricity.
• As fuel in bipropellant rocket vehicles.
• In alcoholic beverages.
• An important industrial ingredient and use as a
  base chemical for other organic compounds include
  ethyl halides, ethyl esters, diethyl ether,
  acetic acid, ethyl amines and to a lesser extent
  butadiene.
• Antiseptic use.
• An antidote.
• Ethanol is easily miscible in water and is a good
  solvent. Ethanol is less polar than water and is
  used in perfumes, paints and tinctures.
• Ethanol is also used in design and sketch art
  markers.
• Ethanol is also found in certain kinds of
  deodorants.