Chapter 1 asac1212

Introduction to Introduction to Organic ChemistryOrganic Chemistry

What is Organic Chemistry?What is Organic Chemistry?

It is defined as the study of hydrocarbons It is defined as the study of hydrocarbons (compounds of hydrogen and carbon) and their (compounds of hydrogen and carbon) and their derivatives.derivatives.

7 million Organic compounds7 million Organic compounds 1.5 million Inorganic compounds1.5 million Inorganic compounds We are enjoying the gifts of organic compounds We are enjoying the gifts of organic compounds

directly or indirectly in our daily life such as directly or indirectly in our daily life such as Animal and plant matter, Foods, Pharmaceuticals, Animal and plant matter, Foods, Pharmaceuticals,

Cosmetics, Fertilizers, Plastics, Petrochemicals, Cosmetics, Fertilizers, Plastics, Petrochemicals, Clothing, Detergents etc.Clothing, Detergents etc.

Carbon CompoundsCarbon Compounds

Organic Compounds Inorganic Compounds

CO2

COXCNXCO3

X=Metal

DifferencesDifferencesOrganic CompoundsOrganic Compounds Inorganic compoundsInorganic compounds

Low melting and boiling pointsLow melting and boiling points High melting and boiling pointsHigh melting and boiling points..

Low solubility in water ; high solubility Low solubility in water ; high solubility in non polar solventsin non polar solvents..

High solubility in water ; low solubility High solubility in water ; low solubility in non polar solventsin non polar solvents..

FlammableFlammable NonflammableNonflammable

Exhibit covalent bondingExhibit covalent bonding.. Exhibit ionic and covalent bondingExhibit ionic and covalent bonding..

Exhibit isomerismExhibit isomerism.. Do not exhibit isomerismDo not exhibit isomerism..

Chemical reactions are usually slowChemical reactions are usually slow.. Chemical reactions are fastChemical reactions are fast..

Solutions are non conductors of Solutions are non conductors of electricityelectricity..

Solutions are conductors of electricitySolutions are conductors of electricity..

General characteristics of organic General characteristics of organic compoundscompounds

Covalent compounds.Covalent compounds. Contain 2 or more elements: C, H, O, N, S, Contain 2 or more elements: C, H, O, N, S,

P.P. Vast numbers of different compounds.Vast numbers of different compounds.

Catenation Ability to form long chains and rings

Why??

Hydrocarbons Hydrocarbons

Simplest

Organic compounds

Alkanes Alkenes Alkynes Arenes

Methane

Ethane, propane

Simplest

Homologous seriesHomologous series

Homologous seriesHomologous series FormulaFormula

AlkanesAlkanes CCnnHH2n+22n+2

AlkenesAlkenes CCnn H H2n2n

AlkynesAlkynes CCnn H H2n-22n-2

AlcoholsAlcohols CCnn H H2n+12n+1 OH OH

Alkyl halidesAlkyl halides CCnn H H2n+12n+1 X (X= F, Cl, Br, I X (X= F, Cl, Br, I((

AldehydesAldehydes CCnn H H2n+12n+1CH OCH O

KetonesKetones C C nnHH2n2n CO CO

Carboxylic acidsCarboxylic acids CCnn H H2n+12n+1 CO CO22 H H

AmidesAmides CCnn H H2n+12n+1 CONH CONH22

AminesAmines CCnn H H2n+12n+1 NH NH22

A series of compounds of similar properties whose molecular formula differ by CH2 between adjacent members of the series.

The members show regular changes in properties

nn 2n+22n+2 Molecular Molecular formulaformula

NameName

11 44 CHCH44 MethaneMethane

22 66 CC22 H H66 EthaneEthane

33 88 CC33 H H88 PropanePropane

44 1010 CC44 H H1010 ButaneButane

55 1212 CC55 H H1212 PentanePentane

66 1414 CC66 H H1414 HexaneHexane

77 1616 CC77 H H1616 HeptaneHeptane

88 1818 CC88 H H1818 OctaneOctane

99 2020 CC99 H H2020 NonaneNonane

1010 2222 CC1010 H H2222 DecaneDecane

As the # C-atoms ↑: reactivity ↓ mp ↑ bp ↑ d ↑ solubility ↓

The first 10 members of the alkanes (CnH2n+2(

Homologous seriesHomologous series

An atom or a group of atoms which impart An atom or a group of atoms which impart characteristics properties to a compound characteristics properties to a compound

is called Functional group. is called Functional group.

Hydrocarbons Hydrocarbons

Type of bonds

Saturated hydrocarbons Unsaturated hydrocarbons

Single bond Double bond Triple bond

Alkanes

Substitution reaction Addition reaction

Which of the following compounds is Which of the following compounds is saturated and which is unsaturated?saturated and which is unsaturated?

H2C CH

C CH

H3CH2C C CH3

CH3

CH3

H2C CH

H2C CH3

HC CH

Chemical formulaChemical formula

Molecular formula

Gives the numbers of each atom in a molecule

Structural formula

Shows, in 2-dimensions,exactly how the atoms are bonded to each other

Ethane C2H6

H3C CH3 C C

H

H

H

H

H

H

=

Q. Write down the molecular and structural formula of:Q. Write down the molecular and structural formula of:

MethaneMethane

Ethane Ethane

Propane Propane

C C

H

H

H

H

H

H

Molecular formula Structural formulaChemical fo

rmula

C2H6

C C C

H

H

H H

H

H

H

HC3H8

CH4 C H

H

H

H

Isomerism Isomerism

Different molecules have the same Different molecules have the same

molecular formula but different structures.molecular formula but different structures.

Isomers

Different physical & chemical properties

ISOMERISM ISOMERISM

STRUCTURAL STRUCTURAL - Chain- Chain- PositionalPositional- FunctionalFunctional

STEREOSTEREO- GeometricalGeometrical- OpticalOptical

Organic Compounds can exist in different forms with the same molecular formula but different structural formulae.

STRUCTURAL ISOMERISMSTRUCTURAL ISOMERISM

When two or more organic compounds have When two or more organic compounds have the same molecular formula but different the same molecular formula but different structures.structures.

Different chemical and physical properties Different chemical and physical properties Types Types

- Chain Isomerism - Chain Isomerism

- Positional Isomerism- Positional Isomerism

- Functional Isomerism - Functional Isomerism

Chain IsomerismChain Isomerism

When carbon atoms are linked together in When carbon atoms are linked together in different ways from compound to different ways from compound to compound.compound.

Nuclear IsomersimNuclear Isomersim CC55HH12 12

n- pentane 2-methylbutane n- pentane 2-methylbutane

2,2-dimethylpropane2,2-dimethylpropane

How many structural isomers does pentane, C5H12, have?

C C C C C

H H H H H

H

HHHHH

H

C C C C

H CH3 H H

H

HHHH

H

C C C

H CH3 H

H

HH

H

CH3

n-pentane

2-methylbutane

2,2-dimethylpropane

24.2

Examples Examples

C C C

H

H

H H

H

H

H

C

H

H

H

C C C

H

H

HC

H

H

H

H

HH

H

Isomerism

Isomerism

Butane C4H10

Molecular formula Structural formula

n-butane

2-methyl propane

Positional IsomersimPositional Isomersim

When the functional groups are in different positions When the functional groups are in different positions on the same carbon chain.on the same carbon chain.

Butan-1-ol Butan-2-olButan-1-ol Butan-2-ol

But-1-ene But-2-ene But-1-ene But-2-ene

2-methylphenol,3-methylphenol,4-methylphenol2-methylphenol,3-methylphenol,4-methylphenol

OH

HO

OH OH

OH

CH3

CH3

H3C

Functional Isomersim Functional Isomersim

Have the same molecular formula but different Have the same molecular formula but different functional groupsfunctional groups

Methoxy methane and Ethanol have the molecular Methoxy methane and Ethanol have the molecular formula Cformula C22HH66OO

Propanal and propanone – CPropanal and propanone – C33HH66OO

H3C O CH3 H3CH2C OH

CH3 CH2 C CH3 C CH3

OH

O

Difference in physical properties Difference in physical properties

Isomerism

Isomerism

Liquid b.p. 78.5 Liquid b.p. 78.5 ººCC

FlammableFlammable

ImMiscible with waterImMiscible with water

Reacts with aqueous potassium Reacts with aqueous potassium permanganate(VII), metallic permanganate(VII), metallic sodium, chlorides of sodium, chlorides of phosphorous etcphosphorous etc

Gas bp. Gas bp. ––24.8 24.8 ººCC

FlammableFlammable

Miscible with waterMiscible with water

Does not react with any of Does not react with any of the reagents mentioned on the reagents mentioned on the left the left

C2H6O

H3C O CH3 H3CH2C OH

STEREO ISOMERISMSTEREO ISOMERISM

When the atoms in a molecule have different When the atoms in a molecule have different arrangements in space.arrangements in space.

They are of two typesThey are of two types - - Geometrical IsomerismGeometrical Isomerism –Different physical –Different physical

properties but similar chemical properties.properties but similar chemical properties. - - Optical IsomerismOptical Isomerism – same physical and – same physical and

chemical properties except that one structure chemical properties except that one structure rotates the plane of polarized light to the right rotates the plane of polarized light to the right and the other rotates it to the left.and the other rotates it to the left.

Geometrical IsomerismGeometrical Isomerism

1. C=C bond in the molecule1. C=C bond in the molecule 2. Molecule has rings2. Molecule has rings 3. Where there is >C=N bond3. Where there is >C=N bond

This can happen in three ways where there is

Cis isomer and Trans isomerCis isomer and Trans isomer

Two types of geometrical isomers areTwo types of geometrical isomers are

Stereo isomers of 2-buteneStereo isomers of 2-butene

Cis but-2-enetrans but-2-

ene

Substituent groups Substituent groups on the same side on the same side of double bond.of double bond.

Substituents on Substituents on opposite sides of opposite sides of double bond.double bond.

Two isomers are not interchangeable.Two isomers are not interchangeable.

Carbon 2 & 3 joined Carbon 2 & 3 joined by double bond.by double bond.

No free rotation.No free rotation. Bonds would have to Bonds would have to

be broken and be broken and reformed.reformed.

+270 kJ mol-1 energy +270 kJ mol-1 energy needed to break this needed to break this bond.bond.

Insufficient energy Insufficient energy available at room available at room temperature.temperature.

Different compounds- different Different compounds- different properties.properties.

Optical IsomerismOptical Isomerism

Asymmetrical carbon:-carbon bonded to 4 Asymmetrical carbon:-carbon bonded to 4 different groups (eg.:- a, b, c, d)different groups (eg.:- a, b, c, d)

Mirror images of each otherMirror images of each other Non superimposableNon superimposable Molecules are said to be chiralMolecules are said to be chiral Different forms are called enatiomersDifferent forms are called enatiomers Rotate the plane of polarised lightRotate the plane of polarised light

Chiral molecules = Asymmetric

Non-superimposable mirror images

Dextrorotatory

Rotates the plane of plane-polarized lightto the right. Represented by (+)-

Levorotatory

Rotates the plane of plane-polarized lighttowards left. Represented by (-)-

TYPES OF OPTICAL ACTIVITYTYPES OF OPTICAL ACTIVITY