2.6 Halogenoalkanes Flashcards

1
Q

What are halogenoalkanes?

A

Halogenoalkanes are organic compounds where at least one hydrogen atom on an alkane has been replaced by a halogen.

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2
Q

What is a nucleophile?

A

A nucleophile is a species that donates a lone pair of electrons in a reaction.

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3
Q

What do the displayed, structural and skeletal formulae of the halogenoalkane with the molecular formula C2H5X look like?

A
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4
Q

What is the difference between primary, secondary and tertiary halogenoalkanes?

A
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5
Q

What is produced when a halogenoalkane reacts with an aqueous alkali, like KOH?

A

An alcohol is produced.
The OH- ion acts as a nucleophile and a nucleophilic substitution reaction takes place.

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6
Q

What is formed when a halogenoalkane reacts with ethanolic potassium hydroxide? What type of reaction takes place?

A

An alkene is produced.
The reaction is an elimination reaction.
(One of the reactions)

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7
Q

What is formed when a halogenoalkane reacts with warm ethanolic ammonia?

A

An amine is produced.
Ammonia acts as the nucleophile in a nucleophilic substitution reaction.

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8
Q

What is formed when a halogenoalkane reacts with alcoholic potassium cyanide?

A

A nitrile is produced.
The cyanide ion acts as the nucleophile in a nucleophilic substitution reaction.

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9
Q

Write the chemical equation for the reaction between bromoethane and ethanolic potassium hydroxide

A
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10
Q

What reaction can be carried out to increase the number of carbons in the halogenoalkane chain?

A

Nucleophilic substitution of the halogenoalkane with a cyanide ion in alcoholic conditions.
The cyanide ion, CN-, contains a carbon atom so the carbon chain increases by one unit.

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11
Q

How can halogenoalkanes be qualitatively identified?

A

Add ethanolic NaOH or KOH, followed by nitric acid then aqueous silver nitrate solution to the halogenoalkane. If a halogenoalkane is present then a silver halide precipitate will form in the solution.

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12
Q

What colour precipitate will form when chloroethane is added to silver nitrate?

A

AgCl - White precipitate

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13
Q

What colour precipitate will form when bromoethane is added to silver nitrate?

A

AgBr - Cream precipitate

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14
Q

What colour precipitate will form when iodoethane is added to silver nitrate?

A

AgI - Yellow precipitate

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15
Q

What is the name of the mechanism for the reaction between a halogenoalkane and ammonia?

A

Nucleophilic substitution

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16
Q

What is the condition required for a halogenoalkane to produce an alcohol rather than an alkene when it reacts with KOH?

A

The KOH needs to be aqueous.
If the KOH is ethanolic, an alkene will be produced.

17
Q

What is the trend in reactivity of primary, secondary and tertiary halogenoalkanes?

A

Tertiary > Secondary > Primary
The tertiary halogenoalkane is the most reactive and the primary halogenoalkane is the least reactive.

18
Q

What is the trend in reactivity of chloro-, bromo- and iodo- halogenoalkanes? Explain in terms of bond enthalpy

A

iodo- > bromo- > chloro-
Iodo- halogenoalkanes are the most reactive. This is because the C-I bond is the weakest (low bond enthalpy) and so it is broken easily.
Chloro- halogenoalkanes are the least reactive because the C-Cl bond has a high bond enthalpy and therefore requires a lot of energy to break

19
Q

What are some common uses of halogenoalkanes?

A
  • Solvents
  • Refrigerants
  • Anaesthetics
20
Q

Why are there tight regulations surrounding the use of halogenoalkanes?

A

Halogenoalkanes are toxic and have a negative impact on the environment, so their use is regulated.

21
Q

What are CFCs?

A

Chlorofluorocarbons.
These are organic compounds containing only carbon, chlorine and fluorine atoms.

22
Q

What is the environmental problem associated with the use of CFCs (chlorofluorocarbons)?

A

CFCs damage the ozone layer. The ozone is in the upper atmosphere and it absorbs a lot of UV radiation.
CFCs are broken down by UV light, releasing a chlorine radical. This chlorine radical reacts with ozone and breaks it down to oxygen. This means there is less protection from UV radiation.

23
Q

Give the equations for the reactions that take place between a chlorine free radical and ozone

A
24
Q

Explain the impact of the bonds C-H, C-F and C-Cl on the atmosphere in reference to the strength of the bond

A

The C-Cl bond is the weakest of the three bonds so it breaks first. This means the C-Cl bond has the greatest impact on the environment as the free radical is produced most easily. The C-H and C-F bonds are much stronger, with C-F having the highest bond strength.

25
Q

What is a reflux setup?

A

Reflux is the boiling setup with a vertical condenser that allows the vapours to return to the same mixture once they condense.