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AS Chemistry. Introduction to organic chemistry. Candidates should be able: t o 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.

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As chemistry

AS Chemistry

Introduction to organic chemistry


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.

Learning Objectives



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.



Benzene – C6H6

Best representations – bonds are intermediate between single and double.


UK oil and gas fields

Norway

Netherlands




Uses of each fraction

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

Fuel gas

Petrol

/ gasoline

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

Naphtha

Used to make chemicals.

Paraffin /

Kerosine

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

Diesel fuel

Fuel for lorries, trains.

Fuel and

lubricating

oil

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

Bitumen

Roofing, and road surfaces.


Compounds in crude oil
Compounds in Crude Oil

  • Alkanes

  • Cycloalkanes

  • Arenes (A2)



Some more alkanes…….


Key terms
Key Terms

  • 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.


Structural isomerism
Structural Isomerism

butane

methylpropane



Naming the alkanes

2-methylpentane

pent counts 5 carbons

an tells you there aren't any double bonds

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

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

Skeletal formulae

3-dimensional structures


Stick skeletal formulae
Stick” (skeletal) formulae

Penguinone

Penguin

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


Windowpane
windowpane

“Stick” (skeletal) formulae

butane

cyclobutane

brokenwindowpane


Benzene
benzene

“Stick” (skeletal) formulae

mercedes benzene


As chemistry1

AS Chemistry

Structural isomerism


Candidates should be able:

  • describe structural isomerism

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

Learning Objectives



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

CHAIN ISOMERISM

STRUCTURAL ISOMERISM

POSITION ISOMERISM

Same molecular formula but different structural formulae

FUNCTIONAL GROUP ISOMERISM

GEOMETRICAL ISOMERISM

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

STEREOISOMERISM

Same molecular formula but atoms occupy different positions in space.

OPTICAL ISOMERISM

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


What are Structural Isomers

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


STRUCTURAL ISOMERISM - INTRODUCTION

COMPOUNDS HAVE THE SAME MOLECULAR FORMULA

BUT DIFFERENT STRUCTURAL FORMULA

Chain different arrangements of the carbon skeleton

similar chemical properties

slightly different physical properties

more branching = lower boiling point


STRUCTURAL ISOMERISM - INTRODUCTION

COMPOUNDS HAVE THE SAME MOLECULAR FORMULA

BUT DIFFERENT STRUCTURAL FORMULA

Chain different arrangements of the carbon skeleton

similar chemical properties

slightly different physical properties

more branching = lower boiling point

Positional same carbon skeleton

same functional group

functional group is in a different position

similar chemical properties - slightly different physical properties


STRUCTURAL ISOMERISM - INTRODUCTION

  • COMPOUNDS HAVE THE SAME MOLECULAR FORMULA

  • BUT DIFFERENT STRUCTURAL FORMULA

  • Chain different arrangements of the carbon skeleton

  • similar chemical properties

  • slightly different physical properties

  • more branching = lower boiling point

  • Positional same carbon skeleton

  • same functional group

  • functional group is in a different position

  • similar chemical properties - slightly different physical properties

  • FunctionalGroup different functional group

  • different chemical properties

  • different 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


STRUCTURAL ISOMERISM - CHAIN

caused by different arrangements of the carbon skeleton

similar chemical properties

slightly different physical properties

more 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.

BUTANE

straight chain

2-METHYLPROPANE

branched

C4H10


STRUCTURAL ISOMERISM - CHAIN

DIFFERENCES BETWEEN CHAIN ISOMERS

ChemicalIsomers show similar chemical properties because

the 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 ones

the greater the degree of branching the lower the boiling point

branching decreases the effectiveness of intermolecular forces

less energy has to be put in to separate the molecules

- 0.5°C

straight chain

- 11.7°C

branched

greater branching

= lower boiling point


STRUCTURAL ISOMERISM - POSITIONAL

molecule has the same carbon skeleton

molecule has the same same functional group... BUT

the functional group is in a different position

have similar chemical properties / different physical properties

Example 1

POSITION OF A DOUBLE BOND IN ALKENES

1

2

2

3

PENT-1-ENE

double bond between carbons 1 and 2

PENT-2-ENE

double bond between carbons 2 and 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.



Chain isomerism – isomers of pentane


STRUCTURAL ISOMERISM - POSITIONAL

molecule has the same carbon skeleton

molecule has the same same functional group... BUT

the functional group is in a different position

have similar chemical properties / different physical properties

Example 2

POSITION OF A HALOGEN IN A HALOALKANE

BUT

1

2

2

1-CHLOROBUTANE

halogen on carbon 1

2-CHLOROBUTANE

halogen on carbon 2

is NOT

3-CHLOROBUTANE

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


STRUCTURAL ISOMERISM - POSITIONAL

molecule has the same carbon skeleton

molecule has the same same functional group... BUT

the functional group is in a different position

have similar chemical properties / different physical properties

RELATIVE POSITIONS ON A BENZENE RING

Example 3

1,2-DICHLOROBENZENE

ortho dichlorobenzene

1,3-DICHLOROBENZENE

meta dichlorobenzene

1,4-DICHLOROBENZENE

para dichlorobenzene



Chain and position isomers of

C4H9OH

butan-1-ol

2-methylpropan-1-ol

butan-2-ol

2-methylpropan-1-ol


Chain isomerism – isomers of hexane



STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

molecules have same molecular formula

molecules have different functional groups

molecules have different chemical properties

molecules have different physical properties

ALCOHOLS and ETHERS

ALDEHYDES and KETONES

ACIDS and ESTERS

MORE DETAILS FOLLOW


STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

ALCOHOLS and ETHERS

NameETHANOL METHOXYMETHANE

ClassificationALCOHOLETHER

Functional GroupR-OHR-O-R

Physical propertiespolar O-H bond gives rise No hydrogen bonding

to hydrogen bonding. low boiling point

get higher boiling point insoluble in water

and solubility in water

Chemical properties Lewis base Inert

Wide range of reactions


STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

ALDEHYDES and KETONES

Name PROPANAL PROPANONE

ClassificationALDEHYDEKETONE

FunctionalGroupR-CHOR-CO-R

Physicalpropertiespolar C=O bond gives polar C=O bond gives dipole-dipole interaction dipole-dipole interaction

Chemical properties easily oxidised to acids of undergo oxidation under

same number of carbons extreme conditions only

reduced to 1° alcohols reduced to 2° alcohols


STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

CARBOXYLIC ACIDS and ESTERS

NamePROPANOIC ACID METHYL ETHANOATE

ClassificationCARBOXYLIC ACIDESTER

Functional GroupR-COOHR-COOR

Physical propertiesO-H bond gives rise No hydrogen bonding

to hydrogen bonding. insoluble in water

get higher boiling point

and solubility in water

Chemical properties acidic fairly unreactive

react with alcohols hydrolysed to acids



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 alkanesubstituents and a carboxylic acid functional group


As chemistry2

AS Chemistry carboxylic acid (

Combustion


Candidates should be able: carboxylic acid (

  • 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

Learning Objectives


Starter activity carboxylic acid (


Combustion of carboxylic acid ( alkanes

Alasken

plan on nor

clues pinhole

police shelter

fans rap if

Alkanes

non-polar

nucleophiles

electrophiles

paraffins

vacation it

cheer mix it

acne riot

cubism onto

bleats

activation

exothermic

reaction

combustion

stable


Combustion of hydrocarbons carboxylic acid (

C6H14 + 9½O2 6CO2 + 7H2O

  • As chain length increases:

    • More oxygen is needed for complete combustion

    • The reactions become more exothermic


Incomplete combustion carboxylic acid (

Often the flame is yellow and luminous

CH4 + 2O2 CO2 + 2H2O

CH4 + 1½O2 CO + 2H2O

CH4 + O2 C + 2H2O


Bunsen Burner carboxylic acid (


Bunsen Burner carboxylic acid (


Carbon monoxide poisoning carboxylic acid (

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 carboxylic acid (

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 carboxylic acid (

Can you complete the table?


Acid Rain carboxylic acid (


Catalytic carboxylic acid ( 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 chemistry3

Free-radical substitution reactions of carboxylic acid ( alkanes

AS Chemistry


Learning Objectives carboxylic acid (

  • 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 carboxylic acid (


Free radical substitution
Free radical substitution carboxylic acid (

chlorination of methane

i.e. homolytic breaking of covalent bonds

Overall reaction equation

CH4 + Cl2

CH3Cl + HCl

Conditions

ultra violet light

excess methane

to reduce further substitution


Free radical substitution mechanism
Free radical substitution mechanism carboxylic acid (

Cl + Cl

CH4 + Cl

CH3 + HCl

CH3 + Cl2

CH3Cl + Cl

CH3 + Cl

CH3 + CH3

ultra-violet

Cl2

initiation step

two propagation steps

termination step

CH3Cl

minor termination step

CH3CH3


Further free radical substitutions
Further free radical substitutions carboxylic acid (

Overall reaction equations

CH3Cl + Cl2

CH2Cl2 + HCl

CH2Cl2 + Cl2

CHCl3 + HCl

CHCl3 + Cl2

CCl4 + HCl

Conditions

ultra-violet light

excess chlorine


As chemistry4

AS Chemistry carboxylic acid (

Cracking


Learning Objectives carboxylic acid (

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 carboxylic acid (


Why crack? carboxylic acid (



Thermal cracking carboxylic acid (

  • Produces a high proportion of alkenes

  • Temperatures range from 400-900oC

  • Pressures up to 7000kPa


Catalytic cracking carboxylic acid (

  • 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 carboxylic acid (

Zeolite catalyst

‘Cat’ cracker


Catalytic cracker carboxylic acid (


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