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OCR A level Chemistry > Alkanes > Flashcards

Alkanes Flashcards

1
Q

Define aliphatic

A

A compound containing carbon and hydrogen joined together in straight chains, branched chains, and non-aromatic rings

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2
Q

Define homologous series

A

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

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3
Q

Define functional group

A

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

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4
Q

Define alicyclic

A

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

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5
Q

Define aromatic

A

A compound containing a benzene ring

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6
Q

Define saturated

A

A compound containing only C-C single bonds

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7
Q

Define unsaturated

A

A compound containing at least one mutiple C-C bond

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8
Q

What is the general formula of an alkane?

A

C2H2n+2

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9
Q

Define structural isomer

A

Compounds with the same molecular formula but different structural formula

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10
Q

What are the 3 ways structural isomerism can occur?

A
  • chain isomers
  • position isomers
  • functional group isomers
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11
Q

Define hydrocarbon

A

A compound containing only carbon and hydrogen atoms

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12
Q

Are alkanes saturated or unsaturated hydrocarbons?

A

Saturated

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13
Q

What shape forms around the carbon atoms in an alkane?

A

Tetrahedral

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14
Q

What 2 factors affect the boiling points of alkanes?

A
  • chain length
  • extent of branching
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15
Q

As branch length increases, what happens to the boiling point?

A

Boiling point increases

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16
Q

Why does boiling point increase with chain length?

A
  • larger chain length means greater contact area betwen molecules
  • meaning London forces between molecules will be greater
  • so more energy is required to overcome the forces
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17
Q

What happens to the boiling point as branching increases?

A

Boiling point decreases

18
Q

Why does boiling point decrease as branching increases?

A
  • the more branched a molecule, the lower the contact area
  • weaker London forces between molecules
  • less energy is needed to overcome the intermolecular forces
19
Q

Why are alkanes relatively unreactive?

A

C-C bonds are non-polar

C-C and C-H bonds are strong

C-H bonds are non-polar as the elements have similar Pauling values

20
Q

What two reactions do alkanes undergo?

A
  • combustion with oxygen
  • reaction with halogens to form haloalkanes
21
Q

How can you tell complete combustion is occurring?

A

A blue flame is seen

22
Q

How can you tell incomplete combustion is occurring?

A

A yellow flame is seen and/or the formation of soot

23
Q

Give the equation for the complete combustion of methane

A

CH4 + 2O2 → 2H2O + CO2

24
Q

When does incomplete combustion occur?

A

When there is insufficient oxygen

25
Q

Why is incomplete combustion dangerous?

A

It produces CO which is a toxic gas

26
Q

What type of reaction is the reaction between alkanes and halogens?

A

Free radical substitution

27
Q

What are the conditions required for the reaction between alkanes and halogens?

A

UV radiation

28
Q

Define radical

A

A species with an unpaired electron

29
Q

Define homolytic bond fission

A

The breaking of a COVALENT bond in which one of the bonded electrons goes to each atom, forming 2 radicals

30
Q

What are the 3 stages of free radical substitution called?

A

Initiation, propagation, termination

31
Q

Why does homolytic fission produce radicals?

A

The bond is split so the electrons are shared equally, i.e both atoms end up with an unpaired electron

32
Q

Why is UV light required for the production of radicals in initiation?

A
  • provides activation energy
  • to break the halogen bond homolytically
33
Q

What is the key feature of initiation in terms of radicals?

A

Radicals are generated

34
Q

What is the key feature of propagation in terms of radicals?

A

For every radical used in a reaction, a new one is produced

35
Q

What is the key feature of termination in terms of radicals?

A

Two radicals react together to form a compound which doesn’t contain a radical

36
Q

Explain why there is more than one product produced by free radical substitution

A
  • Substitution of any of the hydrogens in the chain can occur
  • Multiple substitutions can occur
37
Q

What is the overall equation for the reaction of C5H12 with Br2 to produce C5H11Br

A

C5H12 + Br2 →C5H11Br + HBr

38
Q

What are the 3 limitations of using free radical substitution in organic synthesis?

A
  • Carbon chain length may vary
  • Further substitution can occur
  • Substitution at different positions of the carbon chain can occur
39
Q

What is the simplest alkane with at least one structural isomer?

40
Q

Why doesn’t the reaction of electrophilic substitution occur in the presence of visible light?

A

Visible light does not provide enough energy to homolytically break the halogen bond

OCR A level Chemistry (30 decks)

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