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AS Chemistry - Unit 2 > Unit 3.2.8 - Haloalkanes > Flashcards

Unit 3.2.8 - Haloalkanes Flashcards

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1
Q

What mechanism makes chloroalkanes from alkanes?

A

Free radical substitution

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2
Q

Draw the mechanism for the free radical substitution reaction between methane and chlorine.

A

See Flash Card

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3
Q

What are the five steps for a free radical substitution mechanism?

A

initiation step, first propagation step, secondary propagation step, termination step and minor termination steps.

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4
Q

What is an essential condition for free radical substitution?

A

UV light

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5
Q

Why is UV light essential during free radical substitution?

A

It is required to break the covalent bonds and form free radicals.

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6
Q

What is a free radical?

A

A species which contains an unpaired electron.

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7
Q

What are free radicals caused by?

A

Homolytic fission of a covalent bond.

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8
Q

What is Homolytic fission?

A

Breaking of a covalent bond in such a way that one electron goes to each atom.

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9
Q

What happens if excess chlorine is used during free radical substitution between methane and chlorine?

A

Further substitution happens until all the hydrogen bonds have been substituted out.

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10
Q

How do you ensure chloromethane is the major product during free radical substitution between methane and chlorine?

A

Use excess methane.

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11
Q

What can chloroalkanes and chlorofluroalkanes be used for?

A

Solvents

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12
Q

What is the main use of CFCs?

A

Aerosols and old fridges.

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13
Q

What happens to CFCs when the are realised into the atmosphere and how does this lead to the breakdown of the ozone layer?

A

CFCs undergo homolytic fission to produce cholorine free radicals and these break down the ozone layer.

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14
Q

Draw the mechanism for how CFCs break down the ozone layer.

A

See flash card

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15
Q

What about haloalkanes means they attract nucleophiles?

A

The CX bond is polar which means the carbon is positively charged.

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16
Q

What is a nucleophile?

A

A species with a lone pair of electrons which can be used to bond with a +ve carbon atom.

17
Q

Name three common nucleophiles and state their formula.

A 
Hydroxide ions (OH-)
Cyanide ions (CN-)
Ammonia (NH3)
18
Q

What reaction happens between haloalkanes and nucleophiles?

A

Nucleophilic substitution.

19
Q

Draw the mechanism for the nucleophilic substitution between a haloalkane and a hydroxide ion.

A

See flash card

20
Q

What is produced when cyanide ions react with haloalkanes?

A

Nitriles

21
Q

Draw the mechanism for the nucleophilic substitution between a haloalkane and a cyanide ion.

A

See flash card

22
Q

When haloalkanes are heated with ethanolic ammonia what do they produce?

A

A primary amine

23
Q

Draw the mechanism for the nucleophilic substitution between a haloalkane and ammonia.

A

See flash card

24
Q

Name the two mechanisms that an OH- ion can have with a haloalkane.

A

Nucleophilic substitution and elimination.

25
Q

What does elimination of a haloalkane produce?

A

Alkene

26
Q

Draw the mechanism for the elimination reaction between a haloalkane and a hydroxide ion.

A

See flash card

27
Q

During elimination where is the hydrogen atom lost from?

A

From the carbon atom next to the carbon attached to the halogen.

28
Q

Why can different products be formed during elimination?

A

It depends which carbon atom the hydrogen is lost from.

29
Q

What decides whether nucleophilic substitution or elimination happens?

A

The conditions.

30
Q

What saying can be used to decide whether a reaction is a nucleophilic substitution or elimination?

A

Cheet pawn

31
Q

What does Cheet Pawn stand for?

A 
Concentrated NaOH
Hot
Ethanol solvent
Elimination
Tertiary/secondary

Primary
Aqueous solvent
Warm
Nucleophilic

32
Q

During elimination what does the hydroxide ion act as?

A

A base.

33
Q

What is a base?

A

A proton acceptor

34
Q

During nucleophilic substitution what does the hydroxide ion act as?

A

Nucleophile

35
Q

How does the rate of reaction change between halogen alkanes?

A

Iodo alkanes > Bromo alkanes > Chloroalkanes > Fluoralkanes

36
Q

Why are Iodo alkanes the most reactive?

A

The C-I bonds are long and easier to break making them more reactive.

37
Q

During elimination which product will be the major one?

A

The one where the carbon atoms in the C=C bond are attached to the most carbons

38
Q

Why is the major product of elimination the one where the carbon atoms in the C=C are attached to the most carbon atoms?

A

It is the most stable

AS Chemistry - Unit 2 (11 decks)

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