Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry > AS - Halogenoalkanes > Flashcards

AS - Halogenoalkanes Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What is a halogenoalkane?

A

An alkane with at least on halogen atom in place of a hydrogen atom.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is the C-H bond in halogenoalkanes polar?

A

Halogen atoms are much more electronegative compared to carbon atoms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a nucleophile?

A

An electron-pair donor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Give three examples of nucleophiles. Name these.

A
  1. OH- / hydroxide ion
  2. CN- / cyanide ion
  3. NH3 / ammonia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe what happens in a nucleophilic substitution reaction with a halogenoalkane.

A

The lone pair of electrons of a nucleophile is attracted towards a partially positively charged carbon atom, attacking the carbon atom.

The C-X bond breaks (X being the halogen atom).

The halogen leaves the molecule becoming a halide ion with the lone pair of electrons. The nucleophile takes the place of the halogen molecule in the alkane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are curly arrows used to show in organic reactions?

A

How electron pairs move.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Halogenoalkanes react with hydroxides to form what?

What type of reaction is this?

A

Alcohols.

Nucleophilic substitution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Halogenoalkanes reacts with cyanide to form what?

What type of reaction is this?

A

Nitriles.

Nucleophilic substitution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What cyanide reactant must be used in the nucleophilic substitution reaction with a halogenoalkane?

What conditions are necessary for the reaction?

A

Ethanolic potassium cyanide (potassium cyanide dissolved in ethanol).

Needs to be warmed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the functional group in nitriles?

A

-C-N where the - between C and N is a triple bond.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

In a nitrile, how is the -CN group counted?

A

Counted as part of the group so the product has one extra carbon in the chain than the starting halogenoalkane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

A reaction between a halogenoalkane and ammonia forms what?

What type of reaction is this?

A

An amine.

Nucleophilic substitution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What reagent is used in the reaction between a halogenoalkane and ammonia?

What conditions are necessary for the reaction?

A

Ethanolic ammonia (ammonia dissolved in ethanol).

Ethanolic ammonia needs to be concentrated, warmed, in excess and under pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What happens in the second step in the nucleophilic substitution reaction between a halogenoalkane and ammonia?

What products are formed?

A

An ammonia molecule takes a hydrogen from the NH3 group of the product formed from the first step to form an ammonium ion and an anime.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can the amine act as a nucleophile from the product of the nucleophilic substitution reaction between a halogenoalkane and ammonia?

A

Because the amine group in the product still has a lone pair of electrons so can react with the halogenoalkane molecules itself.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What determines the reactivity of halogenoalkanes in nucleophilic substitution reactions?

Which halogenoalkanes react faster and why?

A

The C-X bond strength.

The C-F bond reacts more slowly than other halogenoalkanes because it’s bond is the strongest.

The C-I bond has the lowest bond enthalpy so it’s easier to break and reacts more quickly than other halogenoalkanes.

17
Q

If different conditions are used, what other reaction may occur with a halogenoalkane other than nucleophilic substitution?

What conditions are necessary for this to occur?

A

Elimination reactions occur in anhydrous conditions (no water present).

18
Q

What is produced in an elimination reaction with a halogenoalkane?

A

An alkane, water and a halogen molecule or ion.

19
Q

How does the hydroxide ion act in an elimination reaction with a halogenoalkane?

A

As a base, removing an H+ ion from the halogenoalkane.

20
Q

Explain what happens during the elimination reaction mechanism between 2-bromopropane and potassium hydroxide.

A
  1. The OH- nucleophile from potassium hydroxide uses its lone pair of electrons to form a bond with one of the hydrogen atoms on the carbon next to the C-Br bond.
  2. The electron pair from the C-H bond now becomes part of the carbon-carbon double bond.
  3. The bromine takes the pair of the electrons in the C-Br bond and leaves as a bromide ion to eventually form potassium bromide.
21
Q

What conditions are necessary for an elimination reaction of a halogenoalkane?

A

Warm the hydroxide ions in ethanol.

Anhydrous conditions.

Heat the mixture under reflux to prevent losing volatile substances.

22
Q

What two ways might a hydroxide ion react with a halogenoalkane?

A

As a nucleophile or a base.

23
Q

Halogenoalkanes are classified as primary, secondary and tertiary. How do you determine this?

A

Primary - halogen atom is at the end of the hydrocarbon chain.

Secondary - the halogen atom is in the body of the chain.

Tertiary - the halogen atom is on a branch of the chain.

24
Q

How can you influence a substitution or elimination reaction?

What conditions favour each reaction?

A

By changing the conditions.

Substitution favoured - aqueous conditions with OH-, using water as the solvent and warmed under reflux.

Elimination favoured - anhydrous conditions with OH-, using ethanol as the solvent and heating under reflux.

25
Q

What happens if a mixture of water and ethanol are used as solvents in reactions with OH- and a halogenoalkane?

A

Both elimination and nucleophilic substitution will occur forming a mixture of the two products.

26
Q

What are CFCs?

A

Chlorofluorocarbons- halogenoalkanes containing chlorine, fluorine and carbon atoms but no hydrogen.

27
Q

Ozone is formed naturally in the upper atmosphere. Why is this beneficial?

A

It absorbs UV radiation.

28
Q

What is the formulae for ozone?

A

O3.

29
Q

What are the dangers of the ozone layer not absorbing UV radiation?

A

Ultraviolet radiation can cause sunburn and skin cancer as it is ionising.

30
Q

How is ozone formed naturally?

Give the two equations for this process.

A

An oxygen molecule is broken down into two free radicals by UV radiation.

O2 —(UV)—> O• + O•

The free radicals attack other oxygen molecules forming ozone.

O2 + O• —> O3

31
Q

What were CFCs used for in the past?

A

Used as coolant gas in fridges, as solvents and as propellants in aerosols.

32
Q

How were CFCs contributing to the hole in the ozone layer?

A

UV radiation causes C-Cl bonds in CFCs to break, forming chlorine free radicals.

Chlorine free radicals catalyse the decomposition of ozone, contributing to the hole in the ozone layer.

33
Q

Give the equa bc tion for the reaction of a chlorine free radical with ozone, and the reaction between the intermediate of this reaction and ozone.

A

Cl• + O3 —> O2 + ClO•

ClO• + O3 —> 2O2 + Cl•

Chemistry (34 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions