Organic Chemistry

1 Chemistry XII ___________________________________________________________________________

FUNDAMENTAL PRINCIPLES OF 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. O || NH4CNO NH2 — C — NH2

(2) (3) (4) (5)

Later on million of organic compound were prepared in laboratory and industry. Organic Chemistry The branch of chemistry which deals with the study of organic compounds is called Organic chemistry. Organic Compounds The compounds which contain carbon as main component are called Organic compounds. Homologous Series A set of similar compounds in which the successive member differ by (-CH 2) group is called Homologous series Terms Number of Carbon Atoms Part of Compound Name 1 Meth2 Eth3 Prop4 But5 Pent6 Hex7 Hept8 Oct9 Non10 Dec11 Undec-

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 2 ________________________________________________________________________ Methane H | H— C — H | H Ethane H H | | H—C—C—H | | H H Propane H H H | | | H—C—C—C—H | | | H H H Butane H H H H | | | | H—C—C—C—C—H | | | | H H H H Pentane H H H H H | | | | | H — C— C — C — C — C — H | | | | | H H H H H Hexane H H H H H H | | | | | | H—C—C—C—C—C—C—H | | | | | | H H H H H H Heptane H H H H H H H | | | | | | | H—C—C—C—C—C—C—C—H | | | | | | | H H H H H H H Octane H H H H H H H H | | | | | | | | H—C—C—C—C—C—C—C—C—H | | | | | | | | H H H H H H H H Author: M. Nawaz Nasir ___________________________________________________________________________

3 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 (1)

(2) (3) (4)

(5) (6) (7)

7.3

SOME FEATURES OF ORGANIC COMPOUNDS Following are some features of organic compounds. Peculiar Behaviour Carbon 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. Non-ionic Character Organic compounds are covalent in nature so they do not show ionic reaction. Rates of Organic Reactions Organic compound have slow rate of reaction. Complex Nature Organic compound are complex in nature. Formula of starch is (C6 H10 O5 ) n . When n may be several thousand. Similar Behavior There exists close relationship between organic compounds, existence of homologous series. Solubility Organic compounds which are soluble in non polar solvents. Isomerism Organic compound show isomerism.

SOURCES OF ORGANIC COMPOUNDS Petroleum, coal and natural gas are vast reservoirs from which many organic compounds are obtained. Coal Coal 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.

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 4 ________________________________________________________________________ bacterial and

high

Wood  chemical    reactions     Peat  high  temperature  pressure     Lignite  pressure     Bituminous coal Dead

plants and trees

i. ii. iii. iv. v. vi.

vii.

7.4

(1)

pressure

Anthracite

Natural Gas Natural gas is a mixture of methane, ethane, propane and butane. It is used as fuel and to produce carbon black and fertilizers. Petroleum Petroleum 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 Refinery Gas It is a mixture of methane, ethane, propane and butane. It is collected below the 20°C. It is used as fuel. Gasoline Gasoline is mixture of hydrocarbon containing 5-8 carbons. It is collected between 40-180°C. It is used as a motor fuel. Kerosene Oil It is mixture of hydrocarbon containing 11 to 12 carbon atoms. It is collected between 160°C-250°C. It is used for heating. Diesel Oil It 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. Residue Residue is a mixture of hydrocarbons. The liquid components are obtained by vacuum distillation. Oil Refineries in Pakistan Attock oil refinery (Morgah near Rawalpindi) Karachi refinery (Karachi) Pak Arab refinery (Muhmud Kot near Multan) Fractional Distillation of Petroleum Suspended 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.

CRACKING OF PETROLEUM The 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. Thermal Cracking The 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

Author: M. Nawaz Nasir ___________________________________________________________________________

5 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 Cracking It 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-Trimethylpentane Octane Number The 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 COMPOUNDS

The organic compounds are classified into two types. 1. Open Chain or Acyclic Compounds 2. Closed Chain or Cyclic Compounds (1) Open Chain or Acyclic Compounds The 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

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 6 ________________________________________________________________________ H H H | | | H— C — C — C — H | | | H CH3 H 2-Methylpropane There are two types of open chain organic compounds. Straight Chain Compounds The organic compound which contains straight chain of carbon atoms. H H H H | | | | H—C—C—C—C—H | | | | H H H H n Butane Branched Chain Compounds The organic compound which contains branch chain of carbon atoms are called branched chain compounds. H H H | | | H—C—C—C—H | | | H CH3 H 2-Methyl Propane (2) Closed Chain Compounds or Cyclic Compounds The 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 Phenol There are two types of closed chain organic compound Homocyclic or Carbocycilc Compounds The organic compound in which ring contains carbon atoms. H H | | H— C — C ─ H | | H─C—C─H | | H H Cyclo Butane

CH3 |

Benzene Toluene Homocyclic are of two types. Alicyclic Compounds The organic compounds which do not contain benzene ring are called alicyclic compounds. Author: M. Nawaz Nasir ___________________________________________________________________________

7 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 | |

Toluene

Phenol

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

N Pyridine

7.7

(1)

(2)

.. ..S Thiophene

.. O .. Furan

FUNCTIONAL GROUP The atoms or group of atoms which confer the characteristic properties of compound called functional group. Types of Compounds on the basis of Functional Group Alkyl Halide The 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 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

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 8 ________________________________________________________________________ (3)

(4)

(5)

(6)

(7)

(8)

ETHER Organic compound in which oxygen atom directly linked with two carbon atoms is called ether. H H | | H—C—O—C—H | | H H Ethyl Methyl Ether Aldehyde Organic compound in which carbon of carbonyl group is linked with at least one hydrogen atom is called aldehyde. O || CH3 — C — H Ethanal Ketone Organic 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 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 Acid Chloride Organic 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 Acid Amide Organic 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

Author: M. Nawaz Nasir ___________________________________________________________________________

9 Chemistry XII ___________________________________________________________________________ (9)

(10)

Ester Organic compound which obtains by replacing H-atoms of carboxylic acid by alkyl group is called ester. O || CH3 — C — OCH3 Methyl Acetate Phenol OH |

Phenol

7.8

(1) (2) (3) (1)

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 sp3 - Hybridization sp2 - Hybridization sp - Hybridization 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 Methane In methane carbon atoms linked with four hydrogen atoms. So on carbon sp3 hybridization takes place. Electronic configuration of C 1s2, 2s2, 2px1, 2py1, 2pz0 1s2, 2s1, 2p1x, 2p1y, 2p1z Suppose 2s, 2px, 2py, 2pz orbitals intermix to form four equivalent sp3 hybrid orbitals. 2s1, 2p1x, 2p1y, 2p1z = 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.

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 10 ________________________________________________________________________ H H

H H

(2)

(3)

Four sigma bonds formed due to sp3 -1s overlapping. 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, 2p1y, 2p0z 1s2, 2s1, 2p1x, 2p1y, 2p1z Suppose 2s, 2px and 2py orbitals intermix to form three equivalent sp2 - hybrid orbitals. 2s1, 2p1x, 2p1y, 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. sp - Hybridization The 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 ― H Electronic configuration of carbon is 1s2, 2s2, 2p1x, 2p1y, 2p0z 1s2, 2s1, 2p1x, 2p1y, 2p1z Suppose 2s and 2px orbitals intermix to form two equivalent sp-hybrid orbitals. 2s2, 2p1x = 2sp In sp hybridization 50% s and 50% p character presents.

Author: M. Nawaz Nasir ___________________________________________________________________________

11 Chemistry XII ___________________________________________________________________________ The angle between two sp hybrid orbitals is 180° 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

1. 2. 3. 4. 5. (1)

(2)

ISOMERISM Two 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 H Ethyl Alcohol Di-methyl Ether Types There are four types of isomerism. Functional Group Isomerism Positional Isomerism Chain Isomerism Meta Isomerism Geometrical Isomerism 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 Position Isomerism Two 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 | | | | | |

Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 12 ________________________________________________________________________ H H H H H H 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 H Cis-Isomer Trans-Isomer

Author: M. Nawaz Nasir ___________________________________________________________________________

13 Chemistry XII ___________________________________________________________________________

ALIPHATIC HYDROCARBONS 8.1

ALKANES

Alkanes 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 Alkanes a. 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 Butane CH3 ― CH ― CH ― CH2 ― CH2 ― CH3 | | CH3 C2H5 3-Ethyle-2-methylhexane (2) Preparation of alkanes i. 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. Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

ii. a.

b.

c.

iv.

v.

Fundamental Principles of Organic Chemistry 14 ________________________________________________________________________ H H H H | | Ni | | C C + H2 H―C―C―H | | 200-300°C | | H H H H Ni H ― 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. From alkyl halide 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 By Reduction Of alkyl halide Alkyl 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 By Zn Alkanes 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 By dry distillation of sodium salt of carboxylic acid with soda lime Soda lime is a mixture of NaOH and calcium oxide CaO CH3COONa + NaOH Na2CO3 + CH4 O || CaO CH3 ― CH2 ― C ― ONa + NaOH Na2CO3 + CH3 ― CH3 This process is called decarboxylation. Kolbe’s Reaction

Author: M. Nawaz Nasir ___________________________________________________________________________

15 Chemistry XII ___________________________________________________________________________ By electrolysis of aqueous solution of Potassium salt of carboxylic acid. Ionization Reaction 2CH3COOK

2CH3COO- +2K+

At anode 2CH3COO-

2e- +2CO2 +CH3-CH3

At cathode 2K+ +2e2K+ +2H2O

2K+ 2KOH +H2

vi. By Reduction of Carbonyl Compounds a. 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 + H2O b. 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 + H2O vii. 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. Ether CH3Br + 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. Combustion Burning 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 Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 16 ________________________________________________________________________ Oxidation of methane under different condition gives different products. a. Incomplete Oxidation Incomplete oxidation results on the formation of carbon mono oxide, water and soot. 3CH4 + 4O2 2CO + 6H2O + C b. 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 Cu H―C O + [O] H―C O | | H OH iii. Nitration When vapours of alkanes and Conc. HNO3 are passed through the copper tube at 400450C° it gives nitroalknes. H H | | H ― C ― H + Conc.HONO2 H ― C ― NO2 + H2O | | H H iv. Halogenation The 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 Author: M. Nawaz Nasir ___________________________________________________________________________

17 Chemistry XII ___________________________________________________________________________ `

Cl | Cl ― C ― Cl + Cl ― Cl | H Mechanism

Cl | Cl ― C ― Cl + HCl | Cl hυ

Cl ― Cl H | Cl. + H ― C ― H | H H | H ― C. + Cl. | H v.

Cl. + Cl. hυ

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

Sulphonation Alkanes 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 alkenes a. 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 Butadiene e. 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 CH2 CH2 CH3 ― CH CH ― CH3 Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 18 ________________________________________________________________________ Ethene 2-Butene CH2 CH ― CH CH2 CH3 ― CH2 ― CH2 ― CH CH2 1-3- Butadiene 1-Pentene CH3 ― CH ― CH2 ― CH2 ― CH CH2 | CH3 5-Methyl 1-Hexane Preparation 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. HH | | H-C -C-Cl+alcoholic KOH

KCl+H2O+CH2=CH2 |

| H H

(2) By dehalogenation of vicinal dihalide A 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 alcohol Alcohol on heating with Conc. H2SO4 is at 180C° gives alkene. H H | | Conc. H2SO4 H-C - C-OH H2O+CH2=CH2 180C° | | H H The 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 Author: M. Nawaz Nasir ___________________________________________________________________________

19 Chemistry XII ___________________________________________________________________________ By Partial Hydrogenation of alkyne Alkyl 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 Reaction By 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-COODisodium Succinate At anode CH2-COOCH2+2e- +2CO2 | || CH2-COO CH2 At cathode 2Na+ +2e2Na 2Na +2H2O 2NaOH+H2 CHEMICAL REACTIONS OF ALKENE Hydrogenation (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 +3H2 Ni +3H Benzene Cyclohexane Addition of Halogen acid Alkenes react with halogen acid to give alkyl halide H H | | H-C = C-H +HCl

H H | | 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 Carbocation Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 20 ________________________________________________________________________ 2nd step Carbocation reacts with halide. H H H H | | | | H-C - C+ +ClH-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 HHH | | | | | | H-C - C=C-H +HBr H-C-C-C-H | | | | H H Br H 1 Propene 2 Bromo Propane Addition of Halogens Cl2 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 H

+Br -

C | C

+Br-Br

Br

+

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

H

C | C H

Br

+

H

Br-C | C -Br H

H

Or Br H | | H-C-C-H | | H Br Addition of H2SO4 Alkenes are soluble in Conc. H2SO4 to give alkyl hydrogen sulphate Author: M. Nawaz Nasir ___________________________________________________________________________

21 Chemistry XII ___________________________________________________________________________ CH2=CH2 +HOSO3H CH3-CH2OSO3H Ethyl hydrogen sulphate Alkyl hydrogen sulphate on boiling with water gives alcohol. CH3=CH2OSO3H+H+ OHCH3-CH2OH+H2SO4 Hydration of alkene Ethene reacts with water in the presence of 10%H2SO4+HgSO4 to give alcohol. CH2=CH2+HOH 10% H2SO4 CH3-CH2OH HgSO 4

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 OO Ethylene ozonide Ethylene ozonide on heating with zinc dust and water gives formaldehyde O || + Zn dust +H2O ZnO +2H-C-H O+ CH3-CH=CH-CH3+

O

CH3-

-CH3

OO 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 O 1, 2 epoxide ethane Epoxide is used for the conversion of lower alcohol to higher alcohols using grignard’s reagent. (b) Hydroxylation Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 22 ________________________________________________________________________ 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) Combustion Burning of alkenes in the presence of oxygen is known as combustion Complete 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 hydrin I.U.P.A.C Names of alkyne 1) Select the longest continuous chain of carbon atoms containing the triple bond. CH35-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. CH35-CH24-CH23-C2≡CH1 1 Pentyle 6) Substituents are given number and names. Examples 1) CH3 1-C2≡C3-CH4-CH35 4 methyl 2 pentyne | CH3 2) CH31 -C2 ≡C3 -CH34 2 Butyne 3) CH36 -C5≡C4 -CH23 -C2 ≡C1-H 1, 4 Hexadiyne 4) CH3 | CH35 -C4 -C3 ≡C2-CH31 4, 4 dimethyl 2 pentyne | CH3 5) CH35 -CH4 -CH23 -C2≡CH1 | CH3 4 Methyl 1 Pentyne Author: M. Nawaz Nasir ___________________________________________________________________________

23 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 HC=C-H+KBr+H2O | | | H H H (3) By dehydration of tetra halide Compound 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 Reaction By 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-OAt anode O || CH- C -O2CO2+2e- +CH || O || || ||| CH -C-OCH Ethyne At cathode 2K+ +2e2K 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 Ethyne Calcium carbide is prepared by heating calcium oxide with carbon. CaO+3C CaC2+CO CHEMICAL REACTIONS OF ALKYNE Addition of water Acetaldehyde is obtained by the addition of water to ethyne in the process of 10%H2SO4+HgSO4 Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 24 ________________________________________________________________________ H OH | | H-C≡C-H+HOH H-C=C-H Vinyl alcohol H OH HO | | rearrangement | | H-C≡C-H H-C-C-H | H Acetaldehyde Addition of Hydrogen Alkynes are reduced to alkanes with H2 in the presence of Pt or Pd or nickel as catalyst Ni 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 Ethane Addition 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 ethane Addition 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 Author: M. Nawaz Nasir ___________________________________________________________________________

25 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 H Addition 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 alkyne a) 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 acid KMnO4 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-OH Acidic nature of alkyne Hydrogen 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 amide Ethyne 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 chloride Ethyne reacts with ammonical cuprous chloride to give red precipitate of copper acetylide. H-C≡C-H+Cu2Cl2+2NH4OH 2NH4Cl+2H2O+Cu-C≡C-Cu Copper acetylide. Reaction with ammonical AgNO3 Ethyne reacts with ammonical silver-nitrate to give white ppt of silver acetylide H-C≡C-H+2AgNO3+2NH4OH 2NH4NO3+2H2O+Ag-C≡C-Ag Silver acetylide Silver acetylide reacts with dil. H2SO4 to give regenerate alkynes. Ag-C≡-C-Ag+dil H2SO4 H-C≡C-H+Ag2SO4 Polymerization of alkyne Illustrations, Composing, Designing and Processing by: Ghulam Farid ___________________________________________________________________________

Fundamental Principles of Organic Chemistry 26 ________________________________________________________________________ Polymerization of acetylene gives different products. Conversion of acetylene to benzene. Acetylene when heated to 400C° in the presence of catalyst gives benzene. C-H H- C

C-H ||| C-H

H-C |||  C-H BENZENE Conversion of acetylene to divinyle acetylene In 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 acetylene Vinyl 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 | | | | | | HH H H H H Formation of chloroprene Vinyl acethylene form chloroprene on treatment with dilute HCl. Cl | +5 -5 H-C≡C-C=C-H+H Cl H-C=C-C=C-H | | | | | H H H H H Chloroprene Chloroprene further polymerize to neoprene, used as synthetic rubber Polymerization Chloroprene Neoprene

Author: M. Nawaz Nasir ___________________________________________________________________________