Organic Chemistry

Chemistry XII ___________________________________________________________________________

FUNDAMENTAL PRINCIPLESOF ORGANIC CHEMISTRY

7.1 INTRODUCTION(1) Vital Force Theory

In the beginning it was believed that organic compound can not be prepared in laboratory and industry. Organic compound obtained from plants and animals. Friedrick Wohler contradicted this idea. He prepared urea in laboratory by ammonium cyanate.

NH4CNO NH2 — C — NH2

Later on million of organic compound were prepared in laboratory and industry.(2) Organic Chemistry

The branch of chemistry which deals with the study of organic compounds is called Organic chemistry.

(3) Organic CompoundsThe compounds which contain carbon as main component are called Organic compounds.

(4) Homologous SeriesA set of similar compounds in which the successive member differ by (-CH2) group is called Homologous series

(5) TermsNumber of Carbon Atoms Part of Compound Name

1 Meth-2 Eth-3 Prop-4 But-5 Pent-6 Hex-7 Hept-8 Oct-9 Non-10 Dec-11 Undec-

Illustrations, Composing, Designing and Processing by: Ghulam Farid___________________________________________________________________________

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Chemistry XII ___________________________________________________________________________

Nonane H H H H H H H H H | | | | | | | | |

H — C — C — C — C — C — C — C — C — C — H | | | | | | | | | H H H H H H H H H

Decane H H H H H H H H H H

| | | | | | | | | |H — C — C — C — C — C — C — C — C — C — C — H

| | | | | | | | | | H H H H H H H H H H

Undecane H H H H H H H H H H H | | | | | | | | | | |

H — C — C — C — C — C — C — C — C — C — C — C — H | | | | | | | | | | | H H H H H H H H H H H

7.2 SOME FEATURES OF ORGANIC COMPOUNDSFollowing are some features of organic compounds.

(1) Peculiar BehaviourCarbon atom from large number of compounds. The carbon atom from strong stable covalent bond with other carbon atoms forming ring, chains of great size. This self linking property of carbon atom is called catenation. Carbon atoms also form stable covalent bond with other atoms like nitrogen or sulphur.

(2) Non-ionic CharacterOrganic compounds are covalent in nature so they do not show ionic reaction.

(3) Rates of Organic ReactionsOrganic compound have slow rate of reaction.

(4) Complex NatureOrganic compound are complex in nature. Formula of starch is . When n may be several thousand.

(5) Similar Behavior There exists close relationship between organic compounds, existence of homologous series.

(6) SolubilityOrganic compounds which are soluble in non polar solvents.

(7) IsomerismOrganic compound show isomerism.

7.3 SOURCES OF ORGANIC COMPOUNDSPetroleum, coal and natural gas are vast reservoirs from which many organic compounds are obtained.CoalCoal is black mineral of veritable origin. It is believed that coal was formed from remains of free buried inside the earth crust about 500 millions years ago. Due to bacterial and chemical reaction on wood it changes into peat. As a result of high temperature and pressure peat changed into coal. The total resources of coal in Pakistan estimated to be 184 billion tons. It is used to make brick. It is used for domestic purposes.


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pressure Anthracite


Natural GasNatural gas is a mixture of methane, ethane, propane and butane. It is used as fuel and to produce carbon black and fertilizers.PetroleumPetroleum is a mixture of hydrocarbon with small amount of sulphur, nitrogen, hydrogen and oxygen. It is thick viscous liquid of brown or black color. It is formed by decomposition of plants and marine animals which buried under the layer of porous rock for millions years ago.Main Fraction of Petroleum

i. Refinery GasIt is a mixture of methane, ethane, propane and butane. It is collected below the 20°C. It is used as fuel.

ii. GasolineGasoline is mixture of hydrocarbon containing 5-8 carbons. It is collected between 40-180°C. It is used as a motor fuel.

iii. Kerosene OilIt is mixture of hydrocarbon containing 11 to 12 carbon atoms. It is collected between 160°C-250°C. It is used for heating.

iv. Diesel OilIt is mixture of hydrocarbon having 12-25 carbon atoms. It is collected between 220°C-350°C. It is used as fuel in diesel engines.

v. ResidueResidue is a mixture of hydrocarbons. The liquid components are obtained by vacuum distillation.

vi. Oil Refineries in PakistanAttock oil refinery (Morgah near Rawalpindi)Karachi refinery (Karachi)Pak Arab refinery (Muhmud Kot near Multan)

vii. Fractional Distillation of PetroleumSuspended solids and dissolved gas are removed from crude oil. Different fraction have different boiling point. The vapours are allowed to pass through condensers which change them into liquid.

7.4 CRACKING OF PETROLEUMThe breaking down of bigger molecules which have high boiling points into smaller molecules which have low boiling points is called cracking. Cracking is generally carried out in the following ways.

(1) Thermal CrackingThe break down of bigger molecules into simpler molecules by heating is called thermal cracking.

H H | | ∆

H— C — C — H H2 + H — C C — H | | | |

H H H H Ethane Ethene


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Chemistry XII ___________________________________________________________________________

H H H H H H | | | | ∆ 550°C | |

H — C — C — C — C — H H — C C — C — C — H + | | | | | | | |H H H H H H H H

n Butane 1 Butene H H H H

| | | |H — C — C C — C — H

| | H H

2 Butene(2) Catalytic Cracking

The breaking down of bigger molecules into simpler molecules in the presence of catalyst is called catalytic cracking.

Al2O3

C16H34 C8H16 + C8H18

Alkane Alkene(3) Steam Cracking

The process in which hydrocarbon in vapour phase mixed with steam and heat in short time above 400°C is used for production of smaller unsaturated hydrocarbons.Application of CrackingIt produces large number of by products which are used for manufacture of drug, plastics, ethanol, fertilizer and synthetic fiber.

7.5 REFORMING OF PETROLEUM The conversion of straight chain alkane into branched chain in the absence of oxygen and in presence of catalyst is called reforming of petroleum. When n octane is heated in the presence of catalyst, it converts into 2, 2, 4-trimethyl pentane.

CH3 CH3

Heat | |CH3 ― (CH2)6 ― CH3 CH3 ― C ― CH2 ― CH ― CH3

n-Octane catalyst | CH3

2, 2, 4-TrimethylpentaneOctane NumberThe percentage of iso-octane in mixture of iso-octane and n-heptane is called octane number. Octane number of branched chain is higher.

7.6 CLASSIFICATION OF ORGANIC COMPOUNDSThe organic compounds are classified into two types.

1. Open Chain or Acyclic Compounds2. Closed Chain or Cyclic Compounds

(1) Open Chain or Acyclic CompoundsThe organic compound in which there are open chain of carbon atom. e.g.

H H H H | | | |

H — C — C — C — C — H | | | | H H H H

n Butane


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H H H | | |

H— C — C — C — H | | |

H CH3 H2-Methylpropane

There are two types of open chain organic compounds.Straight Chain CompoundsThe organic compound which contains straight chain of carbon atoms.

H H H H | | | |

H — C — C — C — C — H | | | | H H H H

n ButaneBranched Chain CompoundsThe organic compound which contains branch chain of carbon atoms are called branched chain compounds.

H H H | | |

H — C — C — C — H | | | H CH3 H2-Methyl Propane

(2) Closed Chain Compounds or Cyclic CompoundsThe organic compounds in which there are closed chain of carbon atoms.

H H | | OH

H — C — C — H | | |

H — C — C — H | | H H

Benzene Cyclo Butane PhenolThere are two types of closed chain organic compoundHomocyclic or Carbocycilc CompoundsThe organic compound in which ring contains carbon atoms.

CH3

|

Benzene TolueneHomocyclic are of two types.Alicyclic CompoundsThe organic compounds which do not contain benzene ring are called alicyclic compounds.


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H H | | H— C — C ─ H | | H ─ C — C ─ H | | H H Cyclo Butane

Thiophene Furan

Chemistry XII ___________________________________________________________________________ H H H H | | | | H — C — C ─ H H — C — C — H | | H ─ C — C ─ H C

| | Cyclo Propane H H Cyclo Butane

Aromatic The organic compounds which contain at least one benzene ring are called aromatic compounds.

OH CH3

| |

Heterocyclic CompoundsThe organic compounds in which ring contain different kind of atoms. e.g.

N

7.7 FUNCTIONAL GROUPThe atoms or group of atoms which confer the characteristic properties of compound called functional group.Types of Compounds on the basis of Functional Group

(1) Alkyl HalideThe organic compound which obtains by replacing H-atoms of alkane by halogen atom (Cl, Br, I, F) is called alkyl halide.

H H H H H | | | | |

H — C — C — Cl H — C — C — C — Br | | | | | H H H H H

Ethyl Chloride Propyl Bromide(2) Alcohol

Organic compound in which hydroxyl group (-OH) directly linked with carbon of open chain compound.

H H H H H | | | | |

H — C — C — OH H — C — C — C — OH | | | | |

H H H H H Ethyl Alcohol Propyl Alcohol


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Pyridine

Phenol Toluene


(3) ETHEROrganic compound in which oxygen atom directly linked with two carbon atoms is called ether.

H H | |

H — C — O — C — H | | H HEthyl Methyl Ether

(4) AldehydeOrganic compound in which carbon of carbonyl group is linked with at least one hydrogen atom is called aldehyde.

O ||

CH3 — C — HEthanal

(5) KetoneOrganic compound in which carbon of carbonyl group is linked with two carbon atoms is called ketone.

O O || ||

CH3 — C — CH3 CH3 — C — CH2 — CH3

Di-methyl Ketone Ethyl Methyl Ketone(6) Carboxylic acid

Organic compound which contains carboxylic group (─COOH) is called carboxylic acid.

H O O | || ||H — C — C — OH CH3 — CH2 — CH2 — C — OH

| H Ethanoic Acid Butanoic Acid

(7) Acid ChlorideOrganic compound which obtains by replacing (-OH) of carboxylic acid by chlorine atom is called acid chloride.

H O | ||H — C — C — Cl | H Acetyl Chloride

(8) Acid AmideOrganic compound which obtains by replacing (-OH) of carboxylic acid by amino group (NH2) is called acid amide.

H O | ||

H — C — C — NH2

| H

Acet amide


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Chemistry XII ___________________________________________________________________________(9) Ester

Organic compound which obtains by replacing H-atoms of carboxylic acid by alkyl group is called ester.

O ||CH3 — C — OCH3

Methyl Acetate(10) Phenol

OH|

Phenol7.8 HYBRIDIZATION

The process of intermixing of orbitals having different shapes and energy to form new orbitals having same shapes and energy is called hybridization.Types

(1) sp3 - Hybridization(2) sp2 - Hybridization(3) sp - Hybridization(1) sp3 - Hybridization

The process of intermixing one s and three p orbitals to form equivalent hybrid orbitals is called sp3 -hybridization. When carbon atoms linked with four other atoms then sp3 - hybridization takes place.

H |

H—C—H | H

MethaneIn methane carbon atoms linked with four hydrogen atoms. So on carbon sp3 - hybridization takes place. Electronic configuration of C

1s2, 2s2, 2px1, 2py

1, 2pz0

1s2, 2s1, 2p1x, 2p1

y, 2p1z

Suppose 2s, 2px, 2py, 2pz orbitals intermix to form four equivalent sp3 hybrid orbitals.2s1, 2p1

x, 2p1y, 2p1

z = 4sp3

In sp3 25% s and 75% p character presents.The angle between two sp3 - hybrid orbitals is 109.28°The geometry of sp3 is tetrahedral.


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H

H H

H

Four sigma bonds formed due to sp3 -1s overlapping.(2) sp2 - Hybridization

The process of intermixing one s and two p orbitals to form three equivalent hybrid orbitals is called sp2 - hybridization. When carbon atom linked with three other atoms then sp2 - hybridization takes place.

H H | |H—C C—H

Ethene In ethene carbon atom linked with three other atoms (one carbon two hydrogen), so on carbon sp2- hybridization takes place. Electronic configuration of C

1s2, 2s2, 2p1x, 2p1

y, 2p0z

1s2, 2s1, 2p1x, 2p1

y, 2p1z

Suppose 2s, 2px and 2py orbitals intermix to form three equivalent sp2 - hybrid orbitals.

2s1, 2p1x, 2p1

y, 2p1z = 3sp2

In sp2 33% s and 67% p character presents.The angle between sp2 hybrid orbitals is 120°The geometry of sp2 hybridization in ethene is trigonal planer.

The pz orbital of one carbon atom overlaps with pz orbital of other carbon atom to form π- bond. Five sigma bonds formed one due to sp2 - sp2 overlapping and four due to sp2 -1s overlapping.

(3) sp - HybridizationThe process of intermixing one s and one p orbitals to form two equivalent hybrid orbitals is called sp hybridization. When carbon atom linked with two other atoms the sp – hybridization takes place. In ethyne carbon atom linked with two other atoms, so on carbon atom sp-hybridization takes place.

H ― C ≡≡ C ― HElectronic configuration of carbon is

1s2, 2s2, 2p1x, 2p1

y, 2p0z

1s2, 2s1, 2p1x, 2p1

y, 2p1z

Suppose 2s and 2px orbitals intermix to form two equivalent sp-hybrid orbitals.2s2, 2p1

x = 2spIn sp hybridization 50% s and 50% p character presents.The angle between two sp hybrid orbitals is 180°


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Chemistry XII ___________________________________________________________________________

The geometry of sp hybridization in ethyne is linear.

py orbitals of each carbon atom overlap to form π- bond. Similarly p z orbitals of each carbon atom overlap to form other π – bond.Three sigma bonds are formed one due to sp-sp overlapping and two due to sp-1s overlapping.

7.9 ISOMERISMTwo or more compounds which have same molecular formula but different structural formula are called isomers and phenomenon is called isomerism.

e.g. C2H6O H H H H | | | |H — C — C — OH H — C — O — C — H | | | |

H H H HEthyl Alcohol Di-methyl Ether

TypesThere are four types of isomerism.

1. Functional Group Isomerism2. Positional Isomerism3. Chain Isomerism4. Meta Isomerism5. Geometrical Isomerism(1) Functional Group Isomerism

Two or more compounds which have same molecular formula but different functional group are called functional group isomers and phenomenon is called functional group isomerism.

H H H H | | | |

H — C — C — OH H — C — O — C — H | | | |

H H H H Ethyl Alcohol Di-methyl Ether

(2) Position IsomerismTwo or more compounds which have same molecular formula and functional group but differ in position of functional group are called positional isomers and phenomenon is called positional isomerism

H H H H H H | | | | | |

H — C — C — C — Cl H — C — C — C — H | | | | | |

H H H H H H


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1-Chloropropane 2-Chloropropane(3) Chain Isomerism

Two or more compounds which have same molecular formula but differ in arrangement of carbon atoms are called chain isomerism.

H H H H H H H| | | | | | |

H — C — C — C — C — H H — C — C — C — H| | | | | | |

H H H H H CH3 H n-Butane 2-Methylpropane

(4) Metamerism Two or more compounds which have same molecular formula but different alkyl group attach to polyvalent atom are called metamers and phenomenon is called metamerism.CH3 — CH2 — O — CH2 — CH3 CH3 — O — CH2 — CH2 — CH3

Diethyl Ether Methyl Propyl Ether(5) Geometrical Isomerism

Two or more compounds which have same molecular formula and structural formula but differ in arrangement of group of atoms are called geometrical isomers and phenomenon is called geometrical isomerism or Cis-trans isomerism.

H H H CH3

| | | |C C C C | | | |

CH3 CH3 CH3 HCis-Isomer Trans-Isomer


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Chemistry XII ___________________________________________________________________________

ALIPHATICHYDROCARBONS

8.1 ALKANESAlkanes are the simplest organic compounds made up of carbon and hydrogen only.They have general formula of Cnh2n+2. Each carbon atom in alkanes is sp3 hybridized and has tetrahedral geometry.

(1) I.U.P.A.C Names of Alkanesa. Select the longest continuous chain of carbon atom and name it according to number

of carbon atoms in the longest chain.b. When two chains contain same chain selected which contain greater number of

substituents.c. Numbering of longest chain of carbon atoms is done from that end from where branch

is near.d. Two of the same groups are written by word di, three by tri, four by tetra, and five by

penta.e. Substituents are given number and name.f. The groups may be written in alphabetical order.

Examples H H H H

| | | |H ― C ― C ― C ― C ― H

| | | | H H H H

n-Butane H H H H

| | | |H ― C ― C ― C ― C ― H

| | | | H H H H

2-Methyl ButaneCH3 ― CH ― CH ― CH2 ― CH2 ― CH3

| | CH3 C2H5

3-Ethyle-2-methylhexane(2) Preparation of alkanesi. Hydrogenation of Unsaturated Hydrocarbons (Sabatier-Sender's Reaction)

Alkanes and alkynes react with H2 in the presence of Ni at 200-300C° to given alkanes.


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H H H H | | Ni | |C C + H2 H ― C ― C ― H | | 200-300°C | | H H H H

NiH ― C ≡≡ ― H + H2 H ― C C ― H

200-300°C | | H H

H H H H | | Ni | |C C + H2 H ― C ― C ― H | | 200-300°C | | H H H H

The hydrogenation can also be carried out with Pt or Pd at room temperature but they are expensive than Ni. The method is of industrial importance.

ii. From alkyl halidea. Wurtz Reaction

Two molecules of alkyl halide react with two atoms of sodium in the presence of ether to give alkanes. H H H H | | Ether | |

H ― C ― Cl +Na + Na + Cl ― C ― H 2NaCl + H ― C ― C ― H | | | | H H H H

b. By Reduction Of alkyl halideAlkyl halide can be reduced to alkanes by nearest hydrogen. Nearest hydrogen is produced by the action of dil.HCl on zinc.

H H | | Zn + dil.HCl

H ― C ― C ― Br + 2H HBr + CH3 ― CH3

| | H H

c. By ZnAlkanes are produced when an alkyl halide reacts with Zn in the presence of an aqueous acid, HCl.

HCl 2CH3 ― CH2 ― CH ― CH3 + Zn ZnBr2 + 2CH3 ― CH2 ― CH2 ― CH3

| Br

HCl 2CH3I + Zn ZnI2 + CH3 ― CH3

iv. By dry distillation of sodium salt of carboxylic acid with soda limeSoda lime is a mixture of NaOH and calcium oxide

CaOCH3COONa + NaOH Na2CO3 + CH4

O || CaO

CH3 ― CH2 ― C ― ONa + NaOH Na2CO3 + CH3 ― CH3

This process is called decarboxylation.v. Kolbe’s Reaction


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Chemistry XII ___________________________________________________________________________ By electrolysis of aqueous solution of Potassium salt of carboxylic acid.

Ionization Reaction2CH3COOK 2CH3COO- +2K+

At anode2CH3COO- 2e- +2CO2 +CH3-CH3

At cathode2K+ +2e- 2K+

2K+ +2H2O 2KOH +H2

vi. By Reduction of Carbonyl Compoundsa. By Clemmensen reduction

This reaction is very useful for direct conversion of carbonyl group in aldehydes and ketones to methyl group or methylene group. The aldehydes and ketones are converted into alkanes. The reagent used is zinc amalgam is HCl.

O || Zn-Hg/HCl

CH3 ― C ― + 4H CH3 ― CH3 + H2O H

O || Zn-Hg/HCl

CH3 ― C ― CH3 + 4H CH3 ― CH2 ― CH3 + H2Ob. Wolf Kishner's Reduction

This reaction is very useful for direct conversion of carbonyl group in aldehydes and ketones to methyl group or methylene group. The aldehydes and ketones are converted into alkanes. The reagent used is hydrazine and KOH in ethylene glycol.

O || NH2-NH2/KOH

CH3 ― C ― H + 4H CH3 ― CH3 + H2O O ||

CH3 ― C ― CH3 + 4H CH3 ― CH2 ― CH3 + H2Ovii. From Grignard's Reagent

Grignard’s reagent can be prepared by treating an alkyl halide with magnesium turnings in the presence of pure dry ether.

EtherCH3Br + Mg CH3 ― Mg ― Br

Grignard’s reagent reacts with water to give alkanes. Br

CH3-δ ― Mg+ δ ― Br + Mg + CH4

OH(3) Reactions of alkanes

i. CombustionBurning of alkanes in the presence of oxygen is known as combustion. Complete combustion of an alkanes yields CO2, H2O and heat.

CH4 + 2O2 CO2 + 2H2O ∆H=-891 kjmol-1

ii. Oxidation


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Oxidation of methane under different condition gives different products.

a. Incomplete OxidationIncomplete oxidation results on the formation of carbon mono oxide, water and soot.

3CH4 + 4O2 2CO + 6H2O + Cb. Catalytic Oxidation

Lower alkanes when burnt in the presence of catalysts, at high temperature and pressure results in the formation of different products.

H H | Cu |H ― C ― H + [O] H ― C ― OH

| | H H

H | Cu

H ― C ― OH + [O] H ― C O + H2O | | H H

CuH ― C O + [O] H ― C O | |

H OHiii. Nitration

When vapours of alkanes and Conc. HNO3 are passed through the copper tube at 400-450C° it gives nitroalknes.

H H | |

H ― C ― H + Conc.HONO2 H ― C ― NO2 + H2O | | H H

iv. HalogenationThe process of replacing hydrogen atom from organic compound by halogen atom is called halogenation.Alkanes react with halogen (Chlorine) in the presence of ultra violet tight and high temperature to give alkyl halide. This method is not good because the mixture of mono, di, tri and tetra compound is formed.

H H | |

H ― C ― H + Cl ― Cl H ― C ― Cl + HCl | | H H

H H | |

H ― C ― Cl + Cl ― Cl Cl ― C ― Cl + HCl | |H H

H Cl| |

Cl ― C ― Cl + Cl ― Cl Cl ― C ― Cl + HCl| |

H H


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Chemistry XII ___________________________________________________________________________

` Cl Cl | |

Cl ― C ― Cl + Cl ― Cl Cl ― C ― Cl + HCl | | H Cl

Mechanismhυ

Cl ― Cl Cl. + Cl.

H H | hυ |

Cl. + H ― C ― H HCl + H ― C.

| | H H H H | |

H ― C. + Cl. H ― C ― Cl | | H H

v. SulphonationAlkanes react with Conc. H2SO4 at40-50C° to give alkyl sulphonic acid. H H

| |H ― C ― H + HOSO3H H ― C ― SO3H + H2O

| | H H

8.2 ALKENES(1) I.U.P.A.C. Names Of alkenesa. Select the longest continuous chain of carbon atoms containing the double bond.

CH3 ― CH2 ― C CH2

| CH3

b. Numbering of carbon atoms is done from that end from where the double bond is near.

CH3 ― CH2 ― C CH2

| CH3

c. If a compound contains one double bond, then replace “ane” of alkanes by “ene”.CH3 ― CH2 ― CH CH2

Butane replaced by butene.d. If a compound contains two double bonds, then replace “ne” of alkane by “deine”.

H H H H | | | |H ― C C ― C C ― H

1, 3 Butadienee. If compound contain three double bonds, then replace “ne” of alkanes by “triene”.f. Write the number of carbon atom to which double bond is linked before the name of

alkenes.g. Substituents are given number and name.

Examples


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CH2 CH2 CH3 ― CH CH ― CH3

Ethene 2-ButeneCH2 CH ― CH CH2 CH3 ― CH2 ― CH2 ― CH CH2

1-3- Butadiene 1-PenteneCH3 ― CH ― CH2 ― CH2 ― CH CH2

| CH3

5-Methyl 1-HexanePreparation Of alkene(1) By dehydroHalogenation of alkyl halide

When alkyl halide reacts with alcoholic KOH removal of halogen atom and hydrogen atom take place from adjacent carbon atoms and alkene is formed.

H H

| | H-C -C-Cl+alcoholic KOH KCl+H2O+CH2=CH2

| |H H

(2) By dehalogenation of vicinal dihalideA compound having two halogen atoms present on adjacent carbon atom is called

vicinal dihalide.Such compound on heating with Zn dust to give alkene

Cl Cl | |

H-C - C-H+Zn ZnCl2+CH2=CH2

| | H H

(3) By dehydration of alcoholAlcohol on heating with Conc. H2SO4 is at 180C° gives alkene.

H H | | Conc. H2SO4

H-C - C-OH H2O+CH2=CH2

| | 180C°

H HThe formation of alkene is easier from tertiary alcohol than primary alcohol and

secondary alcohol H H

| | 98% H2SO4

H-C - C-OH H2O+CH2=CH2

| | 170-180 C°

H H H CH3

| | 62% H2SO4

H-C - C-OH CH2=CH-CH3 +H2O | | 87C° H H 1 Propene

H CH3

| | 46% H2SO4

H-C - C-OH CH2=C-CH3 +H2O | | 87C° | H H 2 Methyl 1 Propene CH3


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+3H2 Ni

Chemistry XII ___________________________________________________________________________

By Partial Hydrogenation of alkyneAlkyl reacts with H2 in the presence of Pt or Pd and high temperature to give alkene.

Pt, Pd H-C≡C-H+H2 H-C=C-H

| | H H Ethene

By Kolbe’s ReactionBy electrolysis of aqueous solution of sodium salt of dicarboxylic acid, we get alkene.Ionization reaction

O ||

CH2-C-ONa CH2-COO- +2Na+

| | CH2-COONa+ CH2-COO-

Disodium SuccinateAt anode

CH2-COO- CH2+2e- +2CO2

| || CH2-COO- CH2

At cathode2Na+ +2e- 2Na

2Na +2H2O 2NaOH+H2

CHEMICAL REACTIONS OF ALKENEHydrogenation (Addition of H2)

Alkene reacts with H2 in the presence of Pt, Pd at room temperature to give alkane. This process is known as catalytic hydrogenation. The catalysts employed are Pt, Pd and Raney Nickel.

Raney Nickel is obtain by dissolving nickel Aluminum alloy in NaOH soln.Ni

+3H

Benzene CyclohexaneAddition of Halogen acid

Alkenes react with halogen acid to give alkyl halideH H H H

| | | | H-C = C-H +HCl H-C-C-Cl

| | H H

The addition of halogen acid to an alkene takes place in two steps.1st step.

Alkene accepts the proton of halogen acid to form carbocation H H

| | H-C = C-H +HCl H-C-C+-Cl-

| | | | H H H H

CarbocationIllustrations, Composing, Designing and Processing by: Ghulam Farid___________________________________________________________________________

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2nd stepCarbocation reacts with halide. H H H H

| | | | H-C - C+ +Cl- H-C-C-Cl

| | | | H H H H

The addition of halogen acid over an unsymmetrical alkene follow Markownikoff’s rule.

The positive part of adding reagent will attack to that carbon atom containing greater number of Hydrogen atom. e.g. H H H H H H | | | | | |

H-C - C=C-H +HBr H-C-C-C-H | | | |H H Br H1 Propene 2 Bromo Propane

Addition of HalogensCl2 and Br2 add to alkenes to give vicinal dichloride or vicinal Bromide respectively.

Cl Cl | |

CH2=CH2 +Cl-Cl CH2- CH2

CH2=CH2 +Br-Br CH2- CH2

| | Br Br

Addition of Br2 gives a trans product.H H H H C C +Br -

|| +Br-Br | Br+

C C

H H H H Bromoniumion

Br- then attacks only from the backside of bromonium ion to form trans addition product.

H H H H

Br- + C Br-C | Br+ | C C -Br

H H H HOr Br H | |

H-C-C-H | | H Br

Addition of H2SO4

Alkenes are soluble in Conc. H2SO4 to give alkyl hydrogen sulphate


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O

Chemistry XII ___________________________________________________________________________

CH2=CH2 +HOSO3H CH3-CH2OSO3HEthyl hydrogen sulphate

Alkyl hydrogen sulphate on boiling with water gives alcohol.CH3=CH2OSO3H+H+ OH- CH3-CH2OH+H2SO4

Hydration of alkeneEthene reacts with water in the presence of 10%H2SO4+HgSO4 to give alcohol.

CH2=CH2+HOH 10% H2SO

4 CH3-CH2OH

HgSO4

The addition of unsymmetrical alkene follow markownikoff rule.“The positive part of adding reagent will attack to that carbon atom containing greater

number of Hydrogen atom”Addition of Ozone (O3)

Alkene reacts with ozone to form ozonide O+ CH2 ____ CH2

| | CH2=CH2 + O O O

O- O Ethylene ozonide

Ethylene ozonide on heating with zinc dust and water gives formaldehyde O ||

+ Zn dust +H2O ZnO +2H-C-H

CH3-CH=CH-CH3+ O CH3- -CH3

O-

CH3- -CH3+ Zn dust || 2CH3-C-H +ZnO +H2O

Oxidation (a) Epoxidation

Per oxy acids like per oxy acetic acid or per oxy benzoic acid react with alkene to form epoxide

O O || ||

CH2=CH2+C6H5-C-O-OH C6H5-C-OH+CH2 ___ CH2

O1, 2 epoxide ethane

Epoxide is used for the conversion of lower alcohol to higher alcohols using grignard’s reagent.(b) Hydroxylation


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The hypothetical addition of hydrogen per oxide to an alkene double bond is called hydrolation.

CH2=CH2 +H-O-OH CH2-CH2

| | OH OH

(c) CombustionBurning of alkenes in the presence of oxygen is known as combustionComplete combustion of an alkene yields CO2, H2O and heat.

C2H4+3O2 2CO2+2H2O+heat(d) Polymerization

In this process smaller molecules combine together to form bigger molecules, polymers

Ether at 400C° and 100atm pressure polymerizes to give polyethylene.(e) Reaction with Hypohalous acid (HOX)

Alkene reacts with Hypohalous acid to form halo alcohol called Halo hydrin. H H | |

H-C=C-H +HOX H-C-C-H | | | | H H Cl OH

Chloro hydrinI.U.P.A.C Names of alkyne

1) Select the longest continuous chain of carbon atoms containing the triple bond.CH3

5-CH4-CH23-C2≡C1-H

|

CH3

2) Numbering of longest chain atoms is done from that end from where the triple bond is near.

3) If a compound contains one triple bond, then replace “ane” of alkane by “yne”.4) If a compound contains two triple bond, then replace “ne” of alkane by “diyne”.

5) Write the number of carbon atom to which triple bond is linked before the name of alkyne. CH3

5-CH24-CH2

3-C2≡CH1

1 Pentyle6) Substituents are given number and names.

Examples1) CH3

1-C2≡C3-CH4-CH35 4 methyl 2 pentyne

| CH3

2) CH31 -C2 ≡C3 -CH3

4 2 Butyne3) CH3

6 -C5≡C4 -CH23 -C2 ≡C1-H 1, 4 Hexadiyne

4) CH3

|CH3

5 -C4 -C3 ≡C2-CH31 4, 4 dimethyl 2

pentyne|

CH3

5) CH35 -CH4 -CH2

3 -C2≡CH1

| CH3 4 Methyl 1 Pentyne


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Chemistry XII ___________________________________________________________________________

Preparation of alkyne (1) By dehalogenation of vicinal dihalide

Vicinal dihalide on treatment with strong base like alcoholic KOH at 160C° eliminates two moles of hydrogen halide to form alkynes

Br Br Br | | |

H-C - C-H+alcoholic KOH H-C=C-H+KBr+H2O

| | | H H H

(3) By dehydration of tetra halideCompound containing two halogens attached to each adjacent carbon atom on heating

with Zinc dust form alkyne.Br Br | |

H-C - C-H+2Zn H-C≡C-H+2ZnBr2

| | Br Br

By Kolbe’s ReactionBy electrolysis method involves electrolysis of aqueous solution of K salts of

unsaturated carboxylic acid Ionization reaction

O O || ||

CH-C-OK CH-C-O- +2K+

O || || || || CH- C -OK CH- C-O-

At anode O

|| CH- C -O- 2CO2+2e- +CH || O || || ||| CH -C-O- CH

Ethyne At cathode

2K+ +2e- 2K 2K +2H2O 2KOH+H2

Industrial preparation of Ethyne Ethyne is usually prepared by the action of water on calcium carbide.

CaC2+2HOH Ca(OH)2 +C2H2

Or H-C≡C-H

EthyneCalcium carbide is prepared by heating calcium oxide with carbon.

CaO+3C CaC2+COCHEMICAL REACTIONS OF ALKYNEAddition of water

Acetaldehyde is obtained by the addition of water to ethyne in the process of 10%H2SO4+HgSO4

H OHIllustrations, Composing, Designing and Processing by: Ghulam Farid___________________________________________________________________________

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| |H-C≡C-H+HOH H-C=C-H

Vinyl alcohol H OH H O | | rearrangement | |H-C≡C-H H-C-C-H

| HAcetaldehyde

Addition of HydrogenAlkynes are reduced to alkanes with H2 in the presence of Pt or Pd or nickel as

catalystNi

H-C≡C-H+H2 H-C=C-H Heat | |

H H H H

| |H-C=C-H+H2 H-C-C-H

| | H H

EthaneAddition of Halogen acid

Alkynes react with halogen chloride and hydrogen bromide to form dihalo alkane. The addition follows markownikoff rule

Br |

H-C ≡ C-H +HBr H-C=C-H | H

Br H Br | | |H-C=C-H+HBr H-C-C-H | | | H H Br

1, 1 di Bromo ethaneAddition of Halogens

One or two molecules of halogens can be added to alkynes giving dihalide and tetra halides respectively.

Br Br | |

H-C≡C-H +Br-Br H- C=C-H Br Br Br Br | | | |

` H-C=C-H +Br-Br H- C- C-H | | Br Br

Addition of NH3

Ethyne reacts with NH3 in the presence of catalyst at 300C° to give methyl nitride.H-C≡C-H +NH3 CH3-CH3 -C≡ N+H2


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Chemistry XII ___________________________________________________________________________Addition of HCN

Ethyne reacts with HCN in the presence of catalyst to give vinyl cyanide. Cu2Cl2/NH4Cl

H-C≡C-H+HCN H-C=C-CN 300C° | |

H HAddition of alcohol

Alcohol adds to acetylene in the presence of KOH to give alkyl vinyl ether.H-C≡C-H +CH3OH H-C=C-OCH3

| | H H

Oxidation of alkynea) Combustion

Alkyne burns in air to give CO2 and H2O.Ethyne (acetylene) burns in air to give CO2 and H2O. Oxyacetylene flame has

temperature of 2800C°. It is used to cut and weld metals.2CH≡CH+5O2 4CO2+2H2O+heat

b) Oxidation with aqueous KMnO4

Ethyne reacts with alkaline KMnO4 to give oxalic acidKMnO4

CH +4O COOH ||| | CH COOH

2 Butyne reacts with 10% aqueous KMnO4 to give two molecules of acetic acid.

O ||

CH3-C≡C-CH3+3O+H2O 2CH3-C-OHAcidic nature of alkyneHydrogen linked with triply bonded carbons and slightly acidic in nature.Reaction with sodium Ethyne reacts with sodium at 110C° to give sodium acetylide

110C° H-C≡C-H+Na H-C≡C-Na+ +1/2 H2

Reaction with sodium amideEthyne reacts with sodium amide to give sodium acetylide acid ammonia

H-C≡C-H+NaH2 H=C≡CNa+NH3

Sodium acetylide can be used for preparing higher alkynes.H-C≡C-Na+CH3Cl H-C≡C-CH3+NaCl

Reaction with ammonical cuprous chlorideEthyne reacts with ammonical cuprous chloride to give red precipitate of copper acetylide.

H-C≡C-H+Cu2Cl2+2NH4OH 2NH4Cl+2H2O+Cu-C≡C-CuCopper acetylide.

Reaction with ammonical AgNO3

Ethyne reacts with ammonical silver-nitrate to give white ppt of silver acetylideH-C≡C-H+2AgNO3+2NH4OH 2NH4NO3+2H2O+Ag-C≡C-Ag

Silver acetylideSilver acetylide reacts with dil. H2SO4 to give regenerate alkynes.

Ag-C≡-C-Ag+dil H2SO4 H-C≡C-H+Ag2SO4

Polymerization of alkynePolymerization of acetylene gives different products.Conversion of acetylene to benzene.Illustrations, Composing, Designing and Processing by: Ghulam Farid___________________________________________________________________________

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Acetylene when heated to 400C° in the presence of catalyst gives benzene. C-H

H- C C-H ||| H-C C-H |||

C-H BENZENEConversion of acetylene to divinyle acetyleneIn the presence of Cu2Cl2+NH4Cl two molecules of acetylene combine to form vinyl acetylene. Cu2Cl2+NH4Cl H-C≡C-H+H-C≡C-H H-C≡C-C=C-H

| | H H

Vinyl acetyleneVinyl acetylene again reacts with acetylene in the presence of Cu2Cl2+NH4Cl to form divinyle acetylene Cu2Cl2+NH4Cl H-C=C-C≡C-H+H-C≡C-H H-C=C-C≡-C-C=C-H

| | | | | | H H H H H HFormation of chloropreneVinyl acethylene form chloroprene on treatment with dilute HCl.

Cl |

H-C≡C-C=C-H+H+5Cl-5 H-C=C-C=C-H | | | | | H H H H H

ChloropreneChloroprene further polymerize to neoprene, used as synthetic rubber

Polymerization Chloroprene Neoprene


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Organic Chemistry

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