systematic carbon chemistry

Learning Outcomes :

Systematic Carbon Chemistry

• Revision of homologous series including alkanes, alkenes, cycloalkanes, amines

• Reactions of alkenes including halogenoalkanes

• Systematic naming of hydrocarbons, including branched hydrocarbons.

Compounds in the same homologous series:-

• have a similar structure (functional group)

• fit a general formula

• have similar properties

• undergo the same reactions

Homologous series Examples of homologous groups include:

Homologous series

General formula

Functional group

Alkanes CnH2n + 2

Alkenes CnH2n C=C

Alkynes CnH2n - 2 C=C

Alkanols CnH2n + 1 OH R – OH

Alkanoic acids CnH2n + 1 COOH R – COOH

Alkanals CnH2n + 1 CHO R – CHO

Alkanes

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Alkanes

General formula CnH2n+2

Name No. C’s

Meth Eth Prop But Pent Hex Hept Oct

1 2 3 4 5 6 7 8

Alkanes

Full Structural formula

CH3CH2CH3

Shortened structural formula

Molecular formula

C3H8

C C C

H

H

H

H

H

H

H

H

Alkanes • Alkanes contain only single carbon to carbon

bonds they are described as saturated hydrocarbons.

• Alkanes are not very reactive (they do not react with acids, alkalis or bromine water).

• They do burn making them important fuels.

CH3CH3 + 3½ O2 2 CO2 + 3 H2O

H = - 1560 kJ mol -1

Structural Isomers

Isomers are compounds with the same molecular formula but different structural formulae.

H

H

C

H

H

H

H

C

H

H C

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.

Take care, the same molecule can be represented in different ways by:

•Drawing the branch below instead of above the carbon chain.

•Drawing the branch at the other end of the chain.

•By drawing a bend in the longest chain.

Isomers or not isomers?

Isomers: Boiling points

Use your understanding of structure and bonding to explain why the boiling point is increasing?

Isomers: Boiling points

As the amount of branching increases, the tendency is for the boiling point to decrease.

The structure is more compact, smaller surface area, weaker London's dispersion forces.

Notes: • Isomers

• Compounds with the same molecular formula but different structural formula

• May belong to different homologues series

• Usually have different physical properties.

Naming Compounds of Carbon

1. Identify the longest chain

2. 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

Worked examples

Naming Organic Compounds, Alkanes

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H

H

C

CH3

H

C

H

H

C

H

H H

H

C

H

2-methylbutane

H

CH3

C

CH3

H

C

H

H

C

H

H H

H

C

H

2,2-dimethylbutane

H

H

C

CH2

H

C

H

H

C

H

H

C

H

H

C

CH2

CH3

C

H

H

CH3 CH2

CH3

H

H

C

H

CH3

C

H

H

7-ethyl-3-methyldecane

H

H

C

H

C

H

C

H

C

H CH3

H

H

C

H

H

CH3

CH3

Draw full structural formula for 2,3,3-trimethylpentane

C2H5

CH3 CH3

CH3CHCHCHCH2CH3

3-ethyl-2,4-dimethylhexane

Problems for you to try:

1. Draw the shortened structural formulae of

a) 2,4-dimethylhexane

b) 4-ethyl-3-methyloctane

c) 2,2,4,4-tetramethylpentane

2. Work out the systematic names of the following compounds.

a) b) c)

Cycloalkanes

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Cycloalkanes:

Name Cyclopropane Cyclobutane Cyclopentane Cyclohexane Cycloalkane

Molecular Formula

C3H6 C4H8 C5H10 C6H12 CnH2n

Structural Formula

(CH2)n

have a ring structure and are saturated (contain only single bonds).

Branched Cycloalkanes

methylcyclopentane

1,4-dimethylcyclohexane 1,2-dimethylcyclohexane

Alkenes

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Alkenes Alkenes are hydrocarbons with the general formula CnH2n

Name No C’s

Eth Prop But Pent Hex Hept Oct

2 3 4 5 6 7 8

Alkenes

Full Structural formula

CH3CHCH2

Shortened structural formula

Molecular formula

C3H6

H

C

H

H

C

H H

C = H

Alkenes

Alkenes contain a carbon to carbon double bond they are described as unsaturated hydrocarbons.

Structural Isomers Ethene has no isomers. Propene is isomeric with cyclopropene

Isomers of alkenes can arise for two reasons

• the position of the double bond in the chain can vary

• the chain can be straight or branched

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.

4. Pick the lowest number and give 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

Worked examples

Naming Organic Compounds, Alkenes

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but-1-ene

H

H

C

H

H

C

H

H

C

H H

C C C =

Naming Organic Compounds, Alkenes

Draw full structural formula for but-2-ene

H

H

C

H

H C

H

H

C

H H

C =

4-methylpent-2-ene

H

H

C

H

H

C

H

H

C

H CH3

C

H

C C C C = H

H

5,5-dimethylhept-2-ene

H

H

C

H

C2H5

C

H

H

C

H

CH3

CH3

C C

H

=

C2H5

C C CH3 C C =

Problems for you to try:

1. Draw the shortened structural formulae of

a) oct-4-ene

b) 3-ethylpent-1-ene

c) 4,4-dimethylhex-2-ene

2. Work out the systematic

names of the following

compounds.

Reactions of Alkenes Addition reactions involving:

• Hydrogen (Hydrogenation)

• Halogens (Halogenation)

• Hydrogen Halides

• Water (Hydration)

Addition Reactions of Alkenes Hydrogenation, the reaction of an alkene with hydrogen is an example of an addition reaction. (2 compounds combine to form a single molecule)

+ H-H

Propene Propane

C C C

H

H

H

H H

HH

HC C C

H

H

H

H H

H

Addition Reactions of Alkenes

Halogenation, the reaction with halogens is another example of an addition reaction

1,2-dibromopropane

colourless

+ Br-Br

orange/red

This can be used for a test for unsaturation

C C C

H

H

H

H H

H

colourless

C C C

H

H

H

Br Br

HH

H

propene

Reaction with Hydrogen Halides

+ H-I

2 -iodopropane

1 -iodopropane

or Normally the H from the halide attaches to the C

which already has the most hydrogen’s.

Reaction of Alkenes

C C C

H

H

H

H H

H

C C C

H

H

H HH

H

H I

C C C

H

H

H HH

H

HI

Alkenes with water • Concentrated sulphuric acid reacts with ethene

• The reaction is an example of Hydration.

• The overall effect of the acid is to combine water with ethene.

• At one time, this was the most important method for manufacturing ethanol from ethene. Nowadays, direct catalytic hydration of ethene is used.

Draw the full structural formulae for the hydration of ethene above.

CH2 = CH2 + H2O CH3CH2 OH

Conc Phosphoric acid

Addition reactions

Naming Halogenoalkanes

Worked examples

H

Br

C

H

Br

C H

H

1,2-dibromoethane

H

Br

C

H

Br

C H

H

1,1-dibromoethane

H

H

C

H

CH3

C

H

Cl

H

C

H

H

CH3

C

H

C

H

3-chloro-2,2-dimethylpentane

Halogen Derivatives (Haloalkanes)

Halogenalkanes and halogenalkenes

CHCl3

CCl4

CH3CCl3

CCl2=CCl2

CH2=CHCl CF2=CF2

CCl2F2

CCl2H2

Chloroform

Freon

Correcting fluid

Gortex, Teflon

Solvent for grease

Vinyl chloride

Paint Stripper

Degreasing agent

Anesthetic

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

CCl3F

CCl2F2

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 the atmosphere. So over time, CFC’s can reach the stratosphere. Here, UV radiation attacks the CFC’s forming free radicals ( ) .

Free radicals react with O3, the reaction is complex, but one Cl free radical can catalyse the break down 1 million O3 molecules. We will look at free radicals in more detail later in the unit!!!

ClO + O Cl + O2

CCl3F CCl2F + Cl U.V.light

Cl + O3 ClO + O2

When UV light breaks bonds, free radicals are formed. Free radicals have unpaired electrons and, as a result, are highly reactive.

Notes: The solubility, boiling point and volatility (ease of evaporation) of a compound can be predicted by considering: • the presence of O-H or N-H bonds, which implies

hydrogen bonding • the spatial arrangement of polar covalent bonds which

could result in a molecule possessing a permanent dipole

• molecular size which would affect London dispersion forces

• the polarities of solute and solvent. Polar or ionic compounds tend to be soluble in polar solvents, non-polar compounds tend to be soluble in non-polar solvents

•

06/02/2019

CfE Higher Chemistry

Unit 2: Natures Chemistry

Alcohols

06/02/2019

Learning Outcomes :

• Give systematic names, structural formulae and isomers for branch chained alcohols.

• The structure of diols, triols and the effect of hydrogen bonding on properties of these molecules.

• Classification of alcohols as primary, secondary and tertiary.

Alcohols

Alcohols

• Homologous Series containing the hydroxyl (-OH) functional

group

• General formula: CnH2n+1OH

*Draw the full structural formula for: Methanol, CH3OH Ethanol C2H5OH Propanol C3H7OH

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Isomers

Propanol has 2 isomers, propan-1-ol and propan-2-ol.

Straight chain isomers of Alkanols:

propan-1-ol

propan-2-ol

C C C

H

H

H

H

H

H

OH

H

C C C

H

H

H

H

OH

H

H

H

* Draw the full structural formula of propanol*

Practice Question

butan-1-ol

H

H

C

H

H

C

H

H

H

C

OH

H

H

C

Naming Alkanols

Practice Question

octan-2-ol

CH3(CH2)5CHOHCH3

Naming Alkanols

Practice Question

3-ethylhexan-2-ol

CH3CH2CH2CH(C2H5)CHOHCH3

Naming Alkanols

Practice Question

3-methylbutan-1-ol

H

H

C

H

H

C

H

H

H

C

OH

H

CH3

C

Naming Alkanols

Other Alcohols Cycloalcohols Cyclohexanol

Diols (dihydric) Ethan-1,2-diol (Anti freeze)

Triols (trihydric) e.g. propan-1,2,3-triol or glycerol is used in cosmetics, paints and nitroglycerine explosives.

*Draw the full structural formula for glycerol*

C

C

C

C

C

C

H

H

H OH

H

H

H

H HH

H

H

C C

OH

H

H H

H

OH

Ethanol C2H5OH

Functional group -OH Hydrogen bonding allows ethanol to dissolve in water,( pH 7. b.p. 78 oC.)

This effect decreases in alcohols as the length of the hydrocarbon chain increases.

C C H

H

H

H OH

H

Hydroxyl group

Ethanol is a good solvent, it behaves both like water and other hydrocarbon solvents.

H

H H

O R O - +

+

-

+

Uses of Alcohols

Uses of Ethanol Solvents: In varnishes (as it evaporates easily), dyes, perfumes and drugs

Cleaning products: Meths is ethanol with added methanol.

Drinks: Ethanol is a natural product of fermentation. Ethanol cannot be more than 15% of the fermentation mixture, as ethanol is a poison and will kill the yeast. In the UK 8 g of ethanol is 1 UNIT.

CH3CH2OH + 3 O2 2 CO 2 + 3 H2O H = - 1367 kJ mol -1

Uses of ethanol Fuel: Increasingly seen as an important fuel.

• Ethanol can be used as a fuel in cars.

• Produced by fermentation

• e.g. sugar cane. It has an

• octane rating of 111. In Brazil about 20% of their ‘petrol’ is ethanol

Uses of methanol Methanol again burns to form carbon dioxide and water.

Methanol can be used as petrol additive or as a fuel in its own right. Octane rating of 114, also ‘clean’ burning. Toxic and corrosive

Classification of Alcohols

In alcohols the Carbon attached to the –OH can be attached to 0, 1, 2 or 3 other Carbon atoms

• 0 or 1 makes it primary as the OH is on the end carbon

• 2 is secondary (the OH is in the middle of a chain)

• 3 is tertiary (in the middle of a chain, opposite a branch)

R1, R2 and R3 can represent Hydrogens or any sized length of carbon chain, like a branch .They are referred to as alkyl groups

R2

R1 C O H

R3

Classification of Alkanols

Classification of Alkanols

C C OH

H

H

H

H

H

C CC

OH

H

H

HH

H

H H C CC

OH

H

H

CH3H

H

H H

primary secondary tertiary

*Give the systematic name for each of the alcohols above*

Practice Question Problems for you to try:

Classify the following as primary, secondary or tertiary alcohols:

A. CH3CH2CH2OH

B.

C.

D.

OH

CfE Higher Chemistry

Unit 2: Natures Chemistry

Carboxylic Acids

06/02/2019

Learning Outcomes :

CARBOXYLIC ACIDS

• In this section you can learn about the characteristic

chemical properties of the family of carboxylic acids,

and find out how they are put to good use in everyday

consumer products.

Carboxylic Acids

• Vinegar’s chemical name is ethanoic acid, sometimes called acetic acid.

• It is a member of a group of compounds called carboxylic acids, which contain the carboxyl functional group (-COOH).

• If it is a straight chain hydrocarbon containing the carboxyl functional group it is known as an alkanoic or carboxylic acid.

Carboxylic (Alkanoic) Acids •They contain the CARBOXYL functional group –COOH

•They have the general formula

CnH2n+1COOH

•Because of the ability of lower molecular sized carboxylic acids to form hydrogen bonds, they are soluble in water.

• They have high b.p.’s for the same reason.

•They also have a sharp smell. Human sweat contains a mixture of these compounds.

Testing Carboxylic Acids (2.2)

ACTIVITY: Testing carboxylic acids. Test a selection of carboxylic acids to for smell, pH and reactivity. NOTES • Show what functional group a carboxylic acid contains and what

the members of the alkanoic acid homologous series look like by drawing the full structural formulae and chemical formulae for the first four members of the alkanoic acid homologous series.

• After completing the experiments make a note of your observations. In particular you should record any trends in smell, pH and reactivity as the length of the carbon chain increases.

Reactions of Carboxylic Acids (2.3) • ACTIVITY: Neutralisation of carboxylic acids.

Neutralise ethanoic acid using sodium hydroxide, using pH paper to check it is no longer acidic. Evaporate off the water to leave the salt, sodium ethanoate.

• NOTES • Write a note on the formation of salts from

carboxylic acids. • Write a word equation and a chemical equation for

the formation of sodium ethanoate from the neutralisation of ethanoic acid and sodium hydroxide.

C H

H

C

H

H

C O - H

H O

propanoic acid

Naming Organic Compounds, Alkanoic acids

C H

CH3

C

H

H

C

H

H

C O - H

CH3 O

3-methylpentanoic acid

Naming Organic Compounds, Alkanoic acids

C H

CH3

C

H

H

C

H

H

C O - H

CH3 O

3,3-dimethylbutanoic acid

Naming Organic Compounds, Alkanoic acids

heptanoic acid

CH3(CH2)5COOH

Naming Organic Compounds, Alkanoic acids

Alkanoic Acids Properties: Acids have a pH below 7. Alkanoic acids are weak acids, so can react with some metals and alkalis.

2 CH3COOH + Mg (CH3COO)2Mg + H2

CH3COOH + NaOH CH3COONa + H2O

Magnesium ethanoate

Sodium ethanoate

CH3COOH + K2CO3 2 CH3COOK + H2O + CO2

Potassium ethanoate

Notes: • Carboxylic acids can react with bases:

metal oxide + carboxylic acid → a salt + water

metal hydroxide + carboxylic acid →salt + water

metal carbonate + carboxylic acid → salt + water + carbon dioxide

06/02/2019

Uses of Carboxylic Acids

Uses for Carboxylic acids

Carboxylic acids are used in:

• some food items. Vinegar is dilute ethanoic acid. This is used in preparations for pickles, salads, sauces, etc.

• the manufacture of soaps. Sodium salts of fatty acids are used in soap and detergent industries.

• medicines. Ethanoic acid is used in making aspirin.

• industrial solvents.

• preparing perfumes and artificial essences used in food manufacturing.

• are produced in your sweat glands. Dogs can track humans by detecting the characteristic blend of these acids in your sweat.

Food preservation Vinegar has been used for

millennia to preserve foods.

There are many other foods where a proportion of ethanoic acid is added not only to enhance flavour, but also to help prevent food spoilage.

Removing lime-scale • The ability of carboxylic acids to react with carbonates

to form salts is exploited in some lime-scale removers. • Lime-scale forms when hard water (water containing

soluble calcium and magnesium salts) is boiled or allowed to evaporate. Under these conditions the soluble salts are changed into insoluble ones. • For example, a water supply containing calcium

hydrogen carbonate will deposit calcium carbonate when boiled.

Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(g)