Hydrocarbons and FuelsAlkanes, Alkenes, and Alkyne, Halogen derivatives, Aromatic

Hydrocarbons, Petrol, Alternative fuels,

IndexCarbon chemistry introduction

Alkanes and Alkenes

Alkynes

Halogen derivatives, CFC’s

Aromatic hydrocarbons

Fuels

Organic Chemistry, the Chemistry of Carbon

Originally chemical compounds were divided into 2 classes:Inorganic or Organic

Organic compounds were derived from living things. It was believed that they contained a ‘vital force’ and couldnot be made from inorganic compounds.

Carbon has the ability to CATENATE, formingcovalent bonds with its own atoms.

CCH H

Organic ChemistryOrganic chemistry is basically the study of compounds containing carbon

(with the exclusion of oxides and carbonates)

There are so many compounds containing carbon that a whole branch of chemistry is devoted to their study.Organic molecules may be as simple as methane,

CH4

or more complicated such as cholesterol

HO

Alkanes and AlkenesAlkane general formula

Alkene general formula

C n H 2n+2

C n H 2n

Structural formula

Name No C’s

MethEthPropButPentHexHeptOct

12345678

CH3CH2CH3 CH3 (CH2)2CH3

Straight Chain

CH3CH2CH3

Branched Chains and unsaturated

Condensed formula

C C C

H

H

H

H

H

H

H

HC C CHH

H

C HHH

H

H

Molecular formula C3H7

Naming Compounds of Carbon

1. Identify the longest chain2. Identify the ‘branches’ and name them.3. Number the carbon atoms on the longest chain, at the end giving

the lowest numbers for the branches.4. Write the branches in alphabetical order.5. If there are more branches with the same name

use di, tri etc

Alkanes

Naming Compounds of Carbon

1. Identify the longest chain, that contains a double bond.2. Identify the ‘branches’ and name them.3. Number the carbon atoms on the longest chain, starting from

the end nearest the double bond. Pick the lowest number to describe the position of the double bond.

4. Write the branches in alphabetical order.5. If there are more branches with the same name

use di, tri etc

Alkenes

Naming Organic Compounds

H

H

C

H

H

C

CH2

H

C

H

H

C

H

H

C

H

H

C

CH2

CH3

C

H

H

CH3 CH2

CH3

1. Decide on the type of compound (ie. consider functional group)

2. Select the longest chain

3. Name the compound with the branched chains in alphabetical order.

alkane

10 C’s decane

7-ethyl-3-methyldecane

H

H

C

H

H

C

CH2

H

C

H

H

C

H

H

C

H

H

C

CH2

CH3

C

H

H

CH3 CH2

CH3

1. Decide on the type of compound (ie. consider functional group)

2. Select the longest chain

4. Name the compound with the branched chains in ascending order.

alkene

7 C’s heptene

hept-2-ene3. Number the C atoms so that the functional group has the lowest number

5,5-dimethylhept-2-ene

H

H

C

H

C2H5

C

H

H

C

H

CH3

CH3

C C

H

=

1. Decide on the type of compound (ie. consider functional group)

2. Select the longest chain

3. Name the compound with the branched chains and halogen in alphabetical order.

halogen (chloroalkane)

5 C’s pentane

3-chloro-2,2-dimethylpentane

H

H

C

H

CH3

C

H

Cl

H

C

H

H

CH3

C

H

C

H

STRUCTURAL ISOMERISM

There are two types1. Chain isomerism.Here the isomers have different arrangements of carbon atoms or different chains. For example there are two compounds with the molecular formula C4H10

H

H

C

H

H

H

H

C

H

HC

H

H

C H

H

C

H

H

C

CH3

H

H

H

C

butane 2-methylpropane

Here, you can see that 2-methylpropane has a side chain.

2. Position Isomerism. Here the isomers have the same carbon skeleton and functional group but the position of the functional group is different.

H

H

C

H

H

H

H

C

Cl

HC H

H

C

H

H

Cl

H

C

H

HC

1-chloropropane 2-chloropropane

H

H

C

H

H

H

H

C

OH

HC H

H

C

H

H

OH

H

C

H

HC

propan-1-ol

propan-2-ol

Reaction of AlkenesReaction with Hydrogen, hydrogenation, an addition reaction

Reaction with halogens,

+ H-H

Propene Propane

1,2 dibromopropanecolourless

C C CH

HH

H H

HC C CH

HH

H H

HHH

C C CH

HH

H H

H+ Br-Br

Orange/red

C C CH

HH

Br Br

HHH

Reaction with Hydrogen Halides

+ H-I

2 -iodopropane

1 -iodopropane

or

Normally the H from thehalide attaches to the C which already has themost hydrogen’s.

C C CH

HH

H H

H

C C C

H

H

H HH

H

H I

C C C

H

H

H HH

H

H I

Alkyne family CnH2n-2

C2H2

Addition reactions with H2 similar to alkenes.

but two stages are possible

Ethene

CaC2 + 2 H2O Ca(OH)2 + C2H2

Ni Catalyst 150 oC

C CH H

1st

2nd

CCH H

C C HH

C C HH +

+ H2

H2

Ethene

Ethane

H H

Halogen Derivatives

Halogenalkanes and Halogenalkenes

CHCl3

CCl4

CH3CCl3

CCl2=CCl2

CH2=CHClCF2=CF2

2-bromo-2-chloro-1,1,1-trifluorethane Halothane

CCl2F2

Lava lamps, non-polar alkanes and chloroalkanesmixed with polar water.

CCl2H2

Chloroform

Freon

Correcting fluid

Gortex, Teflon

Solvent for grease

Vinyl chloride

Paint Stripper

Degreasing agent

Halogen Derivatives, CFC’s

All CFC’s are very unreactive, are not flammable and not toxic. They are used as flame retardants.

CCl3F

CCl2F2

Chlorofluorocabons CFC’s

e.g. 1,1,1,2-tetrafluoroethane is used as a refrigerant.

Used as a blowing agent to make expanded foam

Recently Hydrofluorocarbons have replaced some CFC’s.

The first refrigerant, and in aerosols.

Ozone destruction O3

CFC’s are very stable, lasting for 100 years in theatmosphere. So over time, CFC’s can reach thestratosphere. Here, UV radiation attacks the CFC’sforming free radicals ( ) .

Free radicals react with O3, the reaction is complex, but one Cl free radical can break down 1 million O3 molecules.

ClO + O Cl + O2

Chlorofluorocabons CFC’s

CCl3F CCl2F + ClU.V.light

Cl + O3 ClO + O2

Aromatic Hydrocarbons

Aromatic carbon molecules contain the benzene ring.

BenzeneF.A. Kekule proposedthe original structure

as a result of a dream.

C6H6

Aliphatic carbon molecules contain the linear chains of carbon ring.

Aromatic carbon molecules containing the benzene ringand aliphatic chains are called Arenes.

The first structures are unstable and the electrons delocalise to form a much more stable structure.

CHCHCH

CHCH CH

Aromatic PropertiesCH3

CH3

CH3

CH3

CH3

CH=CH2

The benzene ring does not contain 3 double bonds, and so does not takepart easily in addition reactions. It is insoluble in water, being non-polar. It burns with a smoky flame as carbon is produced.

Aromatic compounds are used in dyes, herbicides, insecticides fungicides,

Methylbenzene (toluene)

Phenylethene (styrene)C6H5CH2CH

1,2 - dimethylbenzene

1,3 - dimethylbenzene

Aromatic compounds

COOH

OH

Cl

Cl

CHCCl3

Poly-aromatic hydrocarbons PAH

DDTdichlorodiphenyltrichloroethane

COOCH3

Aspirin2-ethanoyloxybenzenecarboxcyclic acid

NHCOCH3

Paracetamol4-hydroxyphenylethanamide

Petrol

Long chain Hydrocarbons tend to burn unevenly in a car engine, causing ‘knocking’. Branched chained hydrocarbons burn more evenly, so prevent’knocking’.

By products from the combustion of petrolare CO, CO2, NOx and unburned Hydrocarbons

The alkane 2,2,4,-trimethylpentane has good antiknock properties

This also has a high octane rating, 100.Straight chain hydrocarbons havea lower octane rating, heptane has anoctane number of 0. Benzene is 106.Unleaded petrol in UK has octane ratingof 95.

Petrol is a blend of different hydrocarbons and this can changedepending on the season. In the winter you would need a petrol which was more volatile. Companies change their blend 3 or 4 times a year.

CC

H

H

H

CH3

CH3

C

H

H

H

C

H

H

C

CH3

H

Petrol

Reforming, this is the process by which straight-chain alkanes undergo a chemical change to change them intonew, smoother burning compounds.High temperatures, pressures and a catalyst are used.Branched-alkanes, cycloalkanes and aromatic compoundsare produced.

Hydrocracking, this takes place at high temperaturesin the presence of hydrogen. Long straight chain hydrocarbons are changed into small branched chain andstraight chain alkanes.

Alternative Fuels, biofuelsBiogas Methane, produced by anaerobic respiration

Ethanol Produced by fermentation, octane rating of 111

MethanolA liquid, made from steam and methane. Octanerating of 114, also ‘clean’ burning. Toxic and corrosive

Hydrogen economy

The dream fuel, but needs electricity to make it.

Fuel Cells 2x more efficient than the internal combustion engine.Requires a source of hydrogen and oxygen.

Did you know?CFC’s where replaced by HFC’s which do not degrade theozone layer. However, they are greenhouse gases 1200x more powerful than CO2.A fridge contains 0.67kg of HFC’s, equivalent to 800 kgof CO2 . For this reason, some fridges now use HC’s, such as butane and propane. These are only 3 to 4x aspowerful a green house gas as CO2.

Did you know?Methane is 23x more powerful a greenhouse gas as CO2. Sewage methane can replace the use of natural gas for the generation of electrical power.

Green house emission

-5 -4 -3 -2 -1 0 1 2 3

Petrol

Diesel

Natural gas

Biogas

Fu

el

Carbon dioxide (kg) / litre of fuel burned

So why does burning biogas give a negative value?