Introduction to Organic Chemistry - Alkanes

What is a homologous series?

Series of compounds containing the same functional group and so general formula and chemical properties.

What does the formula of each member of a homologous series differ by?

-CH₂

What is a functional group?

Single atom/ group of atoms that gives the compounds particular chemical properties.

What does general formula represent?

Any member of a homologous series

Alkane general formula

C_nH_2n+2

Alkene general formula

C_nH_2n

What does molecular formula show?

Exact number of atoms of each type.

What does empirical formula?

The simplest whole number ratio of atoms

What does structural formula show?

How atoms are grouped together in a molecule (written)

What does displayed formula show?

All the atoms and all the bonds in a molecule (drawn)

What is skeletal formula?

Simplified structural formula showing only carbon-carbon bonds (as lines) and any functional groups.

What does the prefix of an organic molecule’s name generally tell you?

Number of carbon atoms present

What does the suffix of an organic molecule’s name generally tell you?

Any functional groups present.

What are isomers?

Compounds with the same molecular formula, but different structures.

What are the two types of isomers?

Structural isomers, Stereoisomers

What are structural isomers?

Molecules with the same molecular formula but different structural formulae.

What are stereoisomers?

Molecules with the same molecular and structural formulae, but with a different arrangement of atoms in space.

Alkene functional group

C=C

Halogenoalkane functional group

C-Hal

Alcohol functional group

-O-H

Aldehyde functional group

-COH

Ketone functional group

-C=O

Carboxylic acid functional group

-COOH

Amine functional group

=NHH

Ester functional group

-C=O-O

Alkane suffix

-ane

Alkene suffix

-ene

Halogenoalkane suffix

-ane

Alcohol suffix

-ol

Aldehyde suffix

-al

Ketone suffix

-one

Carboxylic acid suffix

-oic acid

Amine suffix

-amine

Ester suffix

-oate

What are hydrocarbon compounds made up of?

Carbon and hydrogen only

What carbon-carbon bonds do saturated hydrocarbons contain?

Single (alkane CnH2n+2)

What carbon-carbon bonds do unsaturated hydrocarbons contain?

Double (CnH2n)

What chain forms the name of the molecule?

The longest

What is the methyl group branch?

CH₃

What is the ethyl group branch?

CH₃CH₂

If there are multiple alkyl groups present, how do you name the molecule?

Position of alkyl group, di-

If there are multiple different alkyl groups present, how do you name the molecule?

In alphabetical order (ethyl,methyl)

What is a cycloalkane?

Molecule containing a ring of carbon atoms and named with the prefix cyclo-

Bond angles in an alkane

109.5

Carbon-Carbon bond length in an alkane

0.15nm

Bond energy values in an alkane and higher than many other bond energy values. What does this suggest?

More energy is required to break bonds so they must be less reactive.

Are alkanes likely to be polar molecules?

No, as carbon and hydrogen have similar electronegativites.

Facts about the carbon-carbon bonds in alkanes

Symmetrical

There is free rotation about the single bond 

What is a structural isomer?

Compounds that have the same molecular formula but a different structural formula.

Why would an isomer have a higher boiling point?

A linear shape would mean more points of contact between molecules, therefore, there would be more Van Der Waals forces which require more energy to overcome leading to a higher boiling point.

What are the 3 groups that structural isomers can be divided into?

Chain isomers

Position isomers

Functional group isomers

What are chain isomers?

Compounds with the same molecular formula but the carbon chains are arranged in different ways.

What are position isomers?

Compounds with the same molecular formula but the position of the functional group on the carbon chain changes.

What are functional group isomers?

Compounds with the same molecular formula but different functional groups.

Example of chain isomer

Branched VS straight down carbon chains. (butane/2-methyl propane)

Example of position isomers

Propan-1-ol and Propan-2-ol

Example of functional group isomers

Propanal + Propanone (usually aldehydes + ketones)

Two products of combustion of hydrocarbons

Carbon Dioxide + Water

If air supply is restricted, what other products can form as a result of combustion of hydrocarbons and what are the dangers associated with them?

Carbon Monoxide (toxic to humans), Soot (global dimming)

What is the world’s main source of organic chemicals?

Crude Oil

What is the main constituent of crude oil?

Alkanes

How does fractional distillation work?

1. Crude oil is vaporised

2. Passed into a tower that is cooler at the top and 

3. The vapour is condensed at different temperatures and the different fractions are obtained

Fractions obtained from crude oil in order of lowest to highest boiling point (top to bottom)

Petroleum Gases

Petrol

Kerosene

Diesel Oil

Lubricating oil and waxes

Fuel Oil

Bitumen

Use of Petroleum Gases

Bottled for fuel for transportation, heating and electricity generation

Use of petrol

Fuel for transportation

Use of kerosene

Jet fuel

Use of diesel oil

Fuel for trucks, buses, and trains.

Use of lubricating oils and waxes

Lubrication and candles

Use of fuel oil

Fuel for Ships

Use of bitumen

Surfacing roads + roofing

Long hydrocarbon chains characteristics

Higher boiling points, More viscous, At bottom of fractionating column

Reasons for fracking

To release natural gas trapped within shale rock to generate electricity.

Process of fracking

1. Drill into shale rock forcing pressurised water mixed with sand into the shale causing the soft rock to break up/fracture.

2. Trapped gas is released and flows to the surface.

What chemicals are added to the water during fracking?

Hydrochloric acid (breaks up shale rock)

Methanol (prevents corrosion in the system)

Reasons for opposition towards fracking

• Ugly and obstructive infrastructure

• Large amounts of water used

• Chemical additions pollute water supplies

• Occasionally causes small earthquakes

• Burning natural gas produces CO₂ 

What is cracking?

Saturated hydrocarbon molecules are broken down into smaller hydrocarbon molecules by heat to obtain more useful alkanes/alkenes.

Reasons for cracking

Low demand fractions are converted into higher demand fractions

Useful hydrocarbons (alkenes) are produced which are not found in crude oil.

What changes bromine water from orange to colourless

Alkenes.

What burns with a smoky flame?

Alkenes

What are the two types of cracking?

Thermal cracking and Catalytic cracking

What do both thermal and catalytic cracking involve?

Breaking of C-C bonds as they are weaker than C-H bonds.

Conditions for thermal cracking

High temperature (700-1200K)

High pressure (up to 7000kPa)

What do the high temperatures in thermal cracking lead to?

The molecule breaks near the end of the chain, giving a high percentage of small alkenes such as ethene.

Conditions for catalytic cracking

Less high temperature (720K)

Slight pressure (slightly greater than atmospheric pressure)

Zeolite catalyst

Benefits of catalytic cracking compared to thermal cracking.

Cheaper and more efficient (lower temperature and pressure)

Zeolite catalyst favours formation of branched alkanes and cycloalkanes, which are widely used in motor fuels. Also produces aromatic hydrocarbons (e.g benzene)

What is reforming?

Process used to obtain more useful fractions from fractions of little use. Under conditions of heat and pressure,branched chain hydrocarbon molecules are formed from longer straight chained hydrocarbons.

Crude oil pollution

1. Crude oil contains traces of impurities from elements (sulphur) in the original plants + animals from which the crude oil was formed.

2. Sulphur burns in oxygen to form sulphur dioxide.

3. Sulphur further reacts with oxygen higher up in the atmosphere to form sulphur trioxide.

4. This reacts with water in the atmosphere forming dilute sulphuric acid

5. This falls as acid rain.

What pollutants are produced when alkanes are burned?

Carbon dioxide

Carbon monoxide

Sulphur dioxide

Nitrogen oxides

Carbon particulates

Unburnt hydrocarbons

Water vapour.

Problems caused by alkane pollutants

Carbon dioxide = greenhouse gas

Carbon monoxide = binds to haemoglobin reducing oxygen transport

Sulphur dioxide = acid rain

Nitrogen oxides = smog and acid rain

Carbon particulates = soot

Unburnt hydrocarbons = reacts with nitrogen oxide to form ground level ozone and smog

Water vapour = excess can enhance greenhouse effect

How can sulphur dioxide be removed from waste gases from furnaces?

Flue gas desulphurisation

Process of Flue gas desulphurisation

1. Slurry of calcium oxide and water is sprayed into flue gas

2. Formation of calcium sulphite

3. This is oxidised to produce calcium sulphate

4. This is widely used as a raw material for making products such as plaster.

What is used in the internal combustion engine?

Petrol (gasoline fraction) is used in the engine where alkanes are vaporised and combusted with air.

Pollutants produced by complete combustion in internal combustion engine

Carbon dioxide 

Water vapour

Pollutants produced by incomplete combustion in internal combustion engine

Carbon Monodixe

How is nitrogen oxide produced by the internal combustion engine?

From the react between N₂ and O₂ in the high temperatures

Pollutants produced by the internal combustion engine

Carbon dioxide, water vapour, carbon monoxide, nitrogen oxides, hydrocarbons (some do not burn)

What do catalytic converters do?

Remove the polluting gases and unburned hydrocarbons from the exhaust gases and turn them into less harmful products. (CO + NO_X + CH → CO₂ + N₂ + H₂O)

What are catalytic converters made of?

Cheap ceramic honeycomb coated with a thin layer of expeisve metals. The reactions take place on the metal-coated surface.

Why do catalytic converters only require small amounts of expensive metals?

The honeycomb shape gives a very large surface area.

Causes of global warming

Burning fossil fuels, deforestation, industrial activities, transportation, agriculture (livestock farming)