AS Chemistry

Introduction to organic

chemistry

Learning Objectives

Candidates should be able:

to recall IGCSE work on crude oil and ‘cracking’.

in a request for a structural formula, to give the minimal detail, using conventional groups, for an unambiguous structure.

to draw and recognise displayed and skeletal formulae.

to recognise the shape of the benzene ring when it is present in organic compounds.

to interpret and use some of the terminology associated with organic chemistry.

Starter activity

Why carbon?

Carbon can form strong covalent bonds with itself to give chains and rings of its atoms joined by C-C covalent bonds. This property is called catenation and leads to the limitless variety of organic compounds possible.

Straight or branched?

Benzene – C6H6

Best representations – bonds are intermediate between single and double.

UK oil and gas fields Norwa

y

Netherlands

Fractionating columns

Fractional distillation

Fuel gas

Petrol / gasoline

Naphtha

Paraffin / Kerosine

Diesel fuel

Fuel and lubricating oilBitumen

Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas

Fuel for cars and motorcycles, also used to make chemicals.

Used to make chemicals.

Fuel for greenhouse heaters and jet engines, manufacture of chemicals.

Fuel for lorries, trains.

Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.

Roofing, and road surfaces.

Uses of each fraction

Alkanes

Cycloalkanes

Arenes (A2)

Compounds in Crude Oil

methane

CH4 hexane C6H14

ethane C2H6 heptane C7H16

propane C3H8 octane C8H18

butane C4H10 nonane C9H20

pentane C5H12 decane C10H22

The names and molecular formulae of the first 10 alkanes

11 Undecane 22 Docosane 33 Tritriacontane

12 Dodecane 23 Tricosane 40 Tetracontane

13 Tridecane 24 Tetracosane 50 Pentacontane

14 Tetradecane 25 Pentacosane 60 Hexacontane

15 Pentadecane 26 Hexacosane 70 Heptacontane

16 Hexadecane 27 Heptacosane 80 Octacontane

17 Heptadecane 28 Octacosane 90 Nonacontane

18 Octadecane 29 Nonacosane 100 Hectane

19 Nonadecane 30 Triacontane 132 Dotriacontahectane

20 Icosane 31 Hentriacontane  

21 Henicosane 32 Dotriacontane  

Some more alkanes…….

Homologous series: a series or family of organic compounds with the same functional group, whose members differ only in the addition of a CH2 group.

Functional group: the specific atom or group of atoms that confers a particular chemical property on a molecule, e.g. the –OH group in ethanol.

Saturated: the molecule contains the maximum amount of hydrogen atoms possible, with no double or triple bonds between atoms.

Key Terms

Structural Isomerism

butane

methylpropane

Cycloalkanes

Naming the alkanes

2-methylpentane

pent counts 5 carbons

2-methyl tells you to add a methyl group on carbon 2

an tells you there aren't any double bonds

Finish by putting in the correct number of hydrogen atoms

Naming the alkanes

2,2-dimethylbutane 2,3-dimethylbutane

3-ethyl-2-methylhexane

Structural formulae

Displayed formulae

3-dimensional structures

Skeletal formulae

real name: 3,4,4,5-tetramethylcyclohexa-2,5-dienone

“Stick” (skeletal) formulae

Penguinone

Penguin

windowpanebrokenwindowpane

butane

cyclobutane

“Stick” (skeletal) formulae

benzenemercedes benzene

“Stick” (skeletal) formulae

AS Chemistry

Structural isomerism

Learning Objectives

Candidates should be able:

describe structural isomerism

deduce the possible isomers for an organic molecule of known molecular formula.

Chain isomerism

Structural Isomerism

What are isomers?

Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space.

(That excludes any different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds.)

TYPES OF ISOMERISM

Occurs due to the restricted rotation of C=C double bonds... two forms… E and Z (CIS and TRANS)

STRUCTURAL ISOMERISM

STEREOISOMERISM

GEOMETRICAL ISOMERISM

OPTICAL ISOMERISM

CHAIN ISOMERISM

Same molecular formula but different structural formulae

Occurs when molecules have a chiral centre. Get two non-superimposable mirror images.

Same molecular formula but atoms occupy different positions in space.

POSITION ISOMERISM

FUNCTIONAL GROUP ISOMERISM

In structural isomerism, the atoms are arranged in a completely different order.

What are Structural Isomers

STRUCTURAL ISOMERISM - INTRODUCTION

COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA

Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point

STRUCTURAL ISOMERISM - INTRODUCTION

COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA

Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point

Positional same carbon skeletonsame functional groupfunctional group is in a different positionsimilar chemical properties - slightly different physical properties

STRUCTURAL ISOMERISM - INTRODUCTION

COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA

Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point

Positional same carbon skeletonsame functional groupfunctional group is in a different positionsimilar chemical properties - slightly different physical properties

Functional Group different functional groupdifferent chemical propertiesdifferent physical properties

• Sometimes more than one type of isomerism occurs in the same molecule.• The more carbon atoms there are, the greater the number of possible isomers

caused by different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point

There are two structural isomers of C4H10. One is a straight chain molecule where all the carbon atoms are in a single row. The other is a branched molecule where three carbon atoms are in a row and one carbon atom sticks out of the main chain.

BUTANEstraight chain

2-METHYLPROPANEbranched

C4H10

STRUCTURAL ISOMERISM - CHAIN

STRUCTURAL ISOMERISM - CHAIN

DIFFERENCES BETWEEN CHAIN ISOMERS

Chemical Isomers show similar chemical properties becausethe same functional group is present.

Physical Properties such as density and boiling point show trends according to the of the degree of branching

Boiling Point “straight” chain isomers have higher values than branched onesthe greater the degree of branching the lower the boiling pointbranching decreases the effectiveness of intermolecular forcesless energy has to be put in to separate the molecules

- 0.5°Cstraight chain

- 11.7°Cbranched

greater branching = lower boiling point

POSITION OF A DOUBLE BOND IN ALKENES

PENT-1-ENEdouble bond between carbons 1 and 2

PENT-2-ENEdouble bond between carbons 2 and 3

1 2 2 3

There are no other isomers with five C’s in the longest chain but there are three other structural isomers with a chain of four carbons plus one in a branch.

Example 1

STRUCTURAL ISOMERISM - POSITIONAL

molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties

Complete task 1 and task 2 in your hand out…..

Chain isomerism – isomers of pentane

1-CHLOROBUTANEhalogen on carbon 1

1 2

Moving the chlorine along the chain makes new isomers; the position is measured from the end nearest the functional group... the third example is 2- NOT 3-chlorobutane.

There are 2 more structural isomers of C4H9Cl but they have a longest chain of 3

2-CHLOROBUTANEhalogen on carbon 2

BUT

is NOT3-CHLOROBUTANE

2

POSITION OF A HALOGEN IN A HALOALKANEExample 2

STRUCTURAL ISOMERISM - POSITIONAL

molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties

STRUCTURAL ISOMERISM - POSITIONAL

1,3-DICHLOROBENZENEmeta dichlorobenzene

1,2-DICHLOROBENZENEortho dichlorobenzene

1,4-DICHLOROBENZENEpara dichlorobenzene

RELATIVE POSITIONS ON A BENZENE RING

Example 3

molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties

Complete task 3 ,4 and 5 in your hand out..

Chain and position isomers of C4H9OH

butan-1-ol

2-methylpropan-1-olbutan-2-ol

2-methylpropan-1-ol

Chain isomerism – isomers of hexane

Position isomerism

STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

molecules have same molecular formulamolecules have different functional groupsmolecules have different chemical propertiesmolecules have different physical properties

ALCOHOLS and ETHERS

ALDEHYDES and KETONES

ACIDS and ESTERS

MORE DETAILS FOLLOW

ALCOHOLS and ETHERS

Name ETHANOL METHOXYMETHANE

Classification ALCOHOL ETHER

Functional Group R-OH R-O-R

Physical properties polar O-H bond gives rise No hydrogen bondingto hydrogen bonding. low boiling pointget higher boiling point insoluble in waterand solubility in water

Chemical properties Lewis base InertWide range of reactions

STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

ALDEHYDES and KETONES

Name PROPANAL PROPANONE

Classification ALDEHYDE KETONE

Functional Group R-CHO R-CO-R

Physical properties polar C=O bond gives polar C=O bond gives dipole-dipole interaction dipole-dipole interaction

Chemical properties easily oxidised to acids of undergo oxidation undersame number of carbons extreme conditions only

reduced to 1° alcohols reduced to 2° alcohols

STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

CARBOXYLIC ACIDS and ESTERS

Name PROPANOIC ACID METHYL ETHANOATE

Classification CARBOXYLIC ACID ESTER

Functional Group R-COOH R-COOR

Physical properties O-H bond gives rise No hydrogen bondingto hydrogen bonding. insoluble in waterget higher boiling pointand solubility in water

Chemical properties acidic fairly unreactivereact with alcohols hydrolysed to acids

STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

What about benzene rings?

Functional group isomerism

A molecular formula C3H6O could be either propanal (an aldehyde) or propanone (a ketone).

All three compounds are aromatic. Aspirin is also a carboxylic acid ( CO2H) and an ester ( CO2CH3). Tylenol is also an alcohol ( OH)

and an amide ( CONH ). Ibuprofen contains alkane substituents and a carboxylic acid functional group

AS Chemistry

Combustion

Learning Objectives

Candidates should be able:

describe the combustion chemistry of alkanes and how these reactions lead to their use as fuels in industry, in the home and in transport

recognise the environmental consequences of:

• carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the internal combustion engine and of their catalytic removal

• gases that contribute to the enhanced greenhouse effect

Starter activity

Combustion of alkanes

Alasken

plan on nor

clues pinhole

police shelter

fans rap if

activation

exothermic

reaction

combustion

stable

vacation it

cheer mix it

acne riot

cubism onto

bleats

Alkanes

non-polar

nucleophiles

electrophiles

paraffins

C6H14 + 9½O2 6CO2 + 7H2O

Combustion of hydrocarbons

As chain length increases:

• More oxygen is needed for complete combustion

• The reactions become more exothermic

Incomplete combustion

CH4 + 2O2 CO2 + 2H2O

CH4 + 1½O2 CO + 2H2O

CH4 + O2 C + 2H2O

Often the flame is yellow and luminous

Bunsen Burner

Bunsen Burner

Two children who died on Corfu were killed by carbon monoxide poisoning, Greek officials have confirmed. A pathologist said very high levels of the gas were found in the bodies of Christianne Shepherd, seven and her brother Robert, six.

Carbon monoxide poisoning

Carbon monoxide poisoning

Carbon monoxide, CO, poisons the body by combining with hemoglobin some 250 times more tightly than O2, thus hindering the transport of O2 to the body's tissues.

Air pollution

Can you complete the table?

Acid Rain

Emission Source Chemical equation (where appropriate)

Problems associated with this emission

CO2

Complete combustion of fuel

CxHy + O2 xCO2 + H2OGreenhouse gas; major contributor to global warming.

CO

Complete combustion of fuel

CxHy + O2 xCO2 + H2O

Toxic gas; combines with haemoglobin and prevents O2 transport. Leads to photochemical smog.

CxHy

Unburnt hydrocarbon fuel

-Some (especially benzene) are toxic and carcinogenic. Leads to photochemical smog.

NON2 and O2 react under high T conditions of car engine

N2 + O2 2NO

Contributes to formation of acid rain and photochemical smog. Linked to respiratory problems.

NOx

2o pollutant formed from oxidation of NO

2NO + O2 2NO2

SO2

Combustion of S impurities in fossil fuels

S + O2 SO2

Choking gas; major contributor to formation of acid rain.

2

y

2

y

2

y

2

1y

Catalytic converters

These help to promote the following reactions:

2CO + 2NO N2 + 2CO2

CO and CxHx are also oxidised by the air:

CO + O2 CO2

e.g. C7H16 + O2 7CO2 + 8H2O

AS Chemistry

Free-radical substitution reactions of

alkanes

Learning Objectives

Candidates should be able:

describe the mechanism of free-radical substitution at methyl groups with particular reference to the initiation, propagation and termination reactions.

describe the substitution of alkanes by chlorine and bromine.

Starter activity

CH4 + Cl2 CH3Cl + HCl

Overall reaction equation

Conditions

ultra violet lightexcess methane

i.e. homolytic breaking of covalent bonds

to reduce further substitution

Free radical substitutionchlorination of methane

CH4 + Cl CH3 + HCl

Cl2 Cl + Cl

CH3 + Cl2 CH3Cl + Cl

CH3ClCH3 + Cl

initiation step

two propagation steps

termination step

ultra-violet

CH3CH3CH3 + CH3

minor termination step

Free radical substitution mechanism

CH3Cl + Cl2 CH2Cl2 + HCl

Overall reaction equations

Conditions ultra-violet light

CH2Cl2 + Cl2 CHCl3 + HCl

CHCl3 + Cl2 CCl4 + HCl

excess chlorine

Further free radical substitutions

AS Chemistry

Cracking

Learning Objectives

Candidates should be able to suggest how ‘cracking’ can be used to obtain more useful alkanes and alkenes of lower Mr from larger hydrocarbon molecules.

Starter activity

FractionthApproximate %

Crude oil Demand

Gases 2 4Petrol and naphtha

16 27

Kerosene 13 8Gas oil 19 23Residue 50 38

Why crack?

One example of a cracking reaction?

• Produces a high proportion of alkenes• Temperatures range from 400-900oC • Pressures up to 7000kPa

Thermal cracking

• Produces a large proportion of branched alkanes, cycloalkanes and aromatic hydrocarbons

• Uses zeolite (crystalline aluminosilicate) catalysts• Temperature around 450oC• Pressure just above atmospheric

Catalytic cracking

Catalytic cracking

Zeolite catalyst

‘Cat’ cracker

Catalytic cracker