StemUp: OCR A A level Chemistry M4 4.1 Basic concepts and hydrocarbons

Define Homologous Series (1)

A series of organic compounds having the same functional group but with each successive member differing by CH2

Define Hydrocarbon (1)

A compound consisting of ONLY Hydrogen and Carbon

Define General Formula (1)

The algebraic formula for homologous series E.g Cn H2n

State the difference between displayed and skeletal formulae (2)

Displayed- Every bond is drawn

Skeletal - Carbon to Hydrogen bonds are not drawn

Define Functional group (1)

A group of atoms responsible for the characteristic reactions of a compound

Define Molecular formula (1)

The actual number of atoms of each element in the compound

What does the term structural formula mean? (2)

- It shows the arrangement of atoms in a molecule without showing every bond

- E.g CH3CH2CH3 - Structural formula for propane

Define aliphatic (2)

A compound containing Carbon and Hydrogen joined together in straight chains, branched chains or non-aromatic rings

Define alicyclic (2)

An aliphatic compound arranged in non-aromatic rings with or without side chains

Define aromatic compounds (1)

A compound containing a benzene ring(s)

Functional group, prefix, and suffix of an alcohol (4)

- Functional group: OH

- Prefix: Hydroxy-

- Suffix: -ol

- Example: Ethanol

Functional group, prefix, and suffix of aldehydes (4)

- Functional group =

- Prefix: formyl-

- Suffix -al

- E.g Ethanal

Functional group, prefix and suffix of ketones (5)

Functional group:

- Prefix: oxo-

- Suffix: -one

- E.g propone

Functional group and suffix of carboxylic acids (3)

- Functional group:

- Suffix: -oic acid

- E.g Ethanoic acid

Functional group and suffix of esters (2)

- Functional group:

- Suffix: -yl oate

- E.g Methyl ethanoate

Functional group and prefixes of haloalkanes (6)

Functional group: C-X

- Prefix: fluoro-, chloro-, bromo-, idodo-

- E.g Chloropropane

What does nomenclature mean? (1)

The system used for naming organic compounds

What does the displayed formula tell us? (1)

The relative positioning of atoms and the bonds between them

Define structural isomers (1)

Compounds that have the same molecular formula but different structural formula

What are the 3 ways in which structural isomers can be formed? (3)

- Alkyl groups can be in different places

- Functional groups can be bonded to different parts

- There can be different functional groups

Define chain isomers (1)

Compounds with the same molecular formula but different arrangement of Carbon atoms

Define positional isomers (2)

- Compounds with the same molecular formula but different position of functional group

- e.g propan-1-ol and propan-2-ol

Define functional group isomers (1)

Compounds with the same molecular formula but different functional group

Define saturated (2)

Saturated means only single C-C bond

Define unsaturated (2)

Multiple carbon-carbon bonds e.g C=C and C≡C

What 3 factors affect the boiling points of a homologous series? (3)

1. Length of the main chain

2. Surface area of contact

3. Branching

Give 2 reasons why alkanes are mostly unreactive (2)

- C-C and C-H have high bond enthalpies

- Very low bond polarity (essentially non polar) as there is a very small difference in electronegativites between C and H in C-H

What is the general formula for a cycloalkane? (1)

CnH2n

Define Radical (1)

A reactive species with an unpaired electron

What is homolytic fission and what does it form? (2)

- Covalent bond breaks

- With each bonded atom getting an electron forming radicals ( the electrons are equally split, one of the bonded electrons goes to each atom)

What is heterolytic fission? (1)

- When a covalent bond breaks

- With one bonded atom getting both of the shared pair of electrons ( unequal splitting of electrons)

What type of bond fission is Radical Substitution? (1)

Homolytic fission

State the 3 steps of radical substitution (4)

- Initiation

- Propagation

- Termination

Give 2 limitations with radical substitution (2)

- Further substitution of termination products

- Lots of termination steps lead to impurities

Describe the condition needed for initiation to occur in radical substitution e.g reacting methane with chlorine (2)

- UV light

- UV light supplies enough energy to break the Cl-Cl bonds by homolytic fission

Describe what happens in the termination step in Radical substitution (1)

All radicals meet other radicals

Methane reacts with Chlorine by radical substitution Describe fully, with equations, the mechanism for this reaction (6)

What is a σ bond (1)

The direct overlap of orbitals between the bonding atoms

What is a π bond (with a diagram)

The sideways overlap of adjacent p orbitals to form a π bond above and below the plane of the molecule

Give 2 differences between a π bond and a σ bond (3)

- π bond has a lower bond enthalpy than a σ bond

- σ bond has electron density between bonding atoms AND π bond has electron density above and below bonding atoms

- σ bond has direct overlap of orbitals but π bond has sideways overlap

What is a stereoisomer? (1)

Compounds with the same structural formula but with a different spatial arrangement of atoms

What 2 things are required for E-Z stereoisomerism to arise? (2)

1. A double C=C bond - which provides limited rotation

2. Two different groups on each Carbon atom around the double bond

Describe what occurs during propagation in radical substitution of Methane with Chlorine (3)

- Chlorine radicals remove H atoms from the Methane to form methane radicals

- These react with Cl2 molecules to form Chloromethane and Cl•

- The new radical continues the chain reaction

What is E/Z isomerism? (3)

- An example of stereoisomerism where

- There is a C=C which provides restricted rotation

- There are 2 priority groups attached to each carbon of the C=C

What is cis-trans isomerism? (1)

A special case of E/Z isomerism ( stereoisomerism in general) where a substituent group on carbon of the C=C group is the same as the other carbon

How would you try reduce further substitution from happening in radical substitution? (1)

Use an excess of the alkane

Why are alkenes more reactive than alkanes? (2)

- The pi bond has a lower bond enthalpy than the σ bond

- Hence more energy is required to overcome the σ bond compared to the pi bond

Define electrophile (1)

A species that accepts a lone pair of electrons

What is the hydration of alkenes and its conditions? State the mechanism. (4)

- Mechanism: Electrophilic addition

- Forming alcohols from alkenes

- Conditions: Steam, H3PO4 catalyst, high temperature and high pressure

- Example: C2H4 + H2O → C2H5OH

What is the mechanism for hydration, hydrogenation and halogenation? (1)

Electrophilic Addition

What is the test for unsaturated compounds? (2)

1. Add bromine water

2. If the bromine water turns orange to colourless there is a C=C bond present

Draw and describe the electrophilic addition between bromine and ethene (3)

1. The Br2 molecules approaches the alkene

2. Electrons in the pi bond induce a temporary dipole in Br2 causing the Br+ to attack the electron dense pi bond whilst also the Br-Br bond breaks by heterolytic fission

3. The positive carbon on the primary carbocation intermediate attracts the Br- ion

What is Markovnikovs rule used for? (1)

Used to determine the major and minor products of electrophilic addition between hydrogen halides and alkenes

What is a primary carbocation? (1)

The positive charge on a carbon atom is attached to 1 alkyl group

What is a secondary carbocation? (1)

The positive charge on a carbon atom is attached to 2 carbon chains (2 alkyl groups)

What is a tertiary carbocation? (1)

The positive charge on a carbon atom is attached to 3 alkyl groups

What type of bond fission occurs when C2H4 reacts with Br2 (2)

The Br-Br bond breaks by heterolytic fission

Draw the polymerisation of ethene into (poly)ethene

What is addition polymerisation? (1)

The joining/adding of momomers to form a polymer

What is the requirement for the monomer to have to become an addition polymer? (1)

Has to contain a C=C bond

Draw the equation for the formation of (poly)but-1-ene

What shape and bond angle do alkanes have? Explain why (5)

- Tetrahedral

- 109.5 degrees

- Electron pairs repel

- C has 4 bonding pairs and 0 lone pairs

- Bonding pairs repel equally

What reactions will alkanes undergo? (1)

Combustion and reactions with halogens

What is incomplete combustion and what does this form? (1)

Combustion under limited oxygen forming CO and/or C (soot)

What are the problems of combusting polymers? (2)

- Can lead to toxic fumes (e.g HCl)

-Or emission of CO2 which can increase global warming and enhance the greenhouse effect

Give 3 ways of dealing and processing waste polymers? (3)

1. Combustion for energy production

2. Use as an organic feedstock for the production of plastics and other organic chemicals

3. Removal of toxic waste products

Suggest how the HCl can be removed from the gases during the combustion of PVC (3)

1. React with an alkali in order to neutralise

2. React base/carbonate

3. Bubble the HCl through water to make HCl (aq)

What are biodegradable polymers? (2)

Polymers in which micro-organisms recognise specific parts of a molecule and decomposes it

What are the benefits to the environment of developing biodegradable and photodegradable polymers? (2)

1. Reduced dependency of finite resources

2. Reduce problems from disposal e.g Emission of CO2, toxic gases, plastic waste

What does a curly arrow show? (1)

The movement of an electron pair

What bond is broken during addition polymerisation? (1)

Pi bond

What carbocation intermediate is the most stable? (1)

Tertiary carbocation

Why is HBr an electrophile? (1)

HBr breaks by heterolytic fission to form H+ which accepts a lone pair of electrons

What type of bond fission occurs when alkenes react with halogens via electrophilic addition? (1)

Heterolytic fission

Disposal of polymers causes environmental damage. Describe 2 ways in which chemists can reduce this environmental damage (1)

- Develop use of photodegradable polymers

- Develop use of biodegradable polymers

State 2 ways in which chemists are trying to minimise the damage to the environment caused by the disposal of halogenated plastics (3)

- Develop and increase use of biodegradable polymers

- Remove HCl by reacting with an alkali/base/bubbling through water

What is an essential condition for the hydration of alkenes? (2)

- Temperature ≥ 100oC

- As you are reacting the alkene with steam

What is a homologous series? (1)

A series of organic compounds having the same functional group but with each successive member differing by CH2

If a compound contains a benzene ring then it is? (1)

Aromatic

If a compound does not contain a benzene ring then it is (1)

aliphatic

If an aliphatic compound contains a non-aromatic ring then it is (1)

alicyclic

What is the reaction between an acid and a base called (1)

A neutralisation reaction

What are isomers? (1)

Two molecules with the same molecular formula but a different arrangement of atoms

What are structural isomers? (1)

Two molecules with the same molecular formula different structural formula

What forces act between alkane molecules? (1)

London forces

Why do longer chained hydrocarbons have stronger London forces? (1)

There are more surface contact areas and more electrons to interact

Why do branched chained alkanes have lower boiling points? (1)

Cannot pack closely together So, smaller molecule surface area

Why is producing carbon monoxide a problem? (3)

- Carbon monoxide binds to haemoglobin

- Less oxygen can be carried around the body

- Oxygen deprivation

What is breaking a covalent bond called? (1)

Bond fission

What is heterolytic fission? (3)

- Bond breaks unevenly

- One bonded atom receives both electrons from COVALENT bond

- Two different substances are formed

What is homolytic fission? (3)

- Bond breaks evenly

- Each bonding atom receives one electron from COVALENT bond

- Two uncharged radicals are formed

What are radicals? (1)

Species with an unpaired electron

Why are radicals very reactive? (1)

They have an unpaired electron

What do Halogens react with Alkanes to form? (1)

Haloalkanes

What is a free radical substitution reaction? (1)

When a hydrogen atom is substituted by chlorine or bromine

Why is a lack of reactivity in everyday polymers an issue? (1)

Makes them non biodegradable and so difficult to dispose of

When is landfill used? (2)

- Plastic is difficult to separate

- Too difficult to recycle

How can plastics be reused? (4)

- Recycled by melting and remoulding

- Cracked into monomers and used as organic feedstock

- Combustion for energy production

Why is burning carefully controlled? (1)

To reduce toxic gases e.g HCl

What do scrubbers do? (1)

They neutralise gases such as HCl allowing them to react with base