CH2 - Halogenoalkanes

  • Created by: zopetre_
  • Created on: 02-06-17 12:38

Describe the structure of halogenoalkanes

They are an homologous series in which one or more of the hydrogen atoms have been replaced by a halogen

General formula CnH2n+1X (x is a halogen)

Formula of a halogenoalkane often shown as RX

Contain a carbon to halogen bond, bond is polar and carbon is + halogenoalkane is -

Dipole means that halogenoalkanes are susceptible to nucleophilic attacks on the + carbon, leading to substitution 

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Describe nucleophilic substitution

A nucleophile has a lone pair of electrons that can be donated to an electron-deficient species


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Describe preparation of alcohols

Nucleophilic substitution is used to prepare alcohols from halogenoalkanes

Reflux is a process of continuous evaporation and condensation

Hydrolysis is a reaction with water to produce a new product

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What are the effects of changing the halogen?

Electronegativity, it decreases as the size of the halogen increases

Bond strength as the substitution reaction involves breaking carbon to halogen bond, stronger for the C-Cl bond as therefore it is the most difficult to break

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Describe the test for halogenoalkanes

RX + NaOH > ROH + Na + X-

X- + Ag+ > AgX

Chlorine - white precipitate

Bromine - cream precipitate

Iodine - yellow precipitate

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Describe the elimination reaction

One that involves the loss of a small molecule to produce a multiple bond


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What are the uses of halogenoalkanes as solvents?

They have a polar and non-polar section so can mix with a variety of polar and non-polar organic substances

They are non-flammable so is an advantage

Chlorocompounds are preferred as they are cheaper

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What are the uses of halogenoalkanes as anaestheti

Many can act as general anaethetics 

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What are the use of halogenoalkanes as refrigerant

Presence of permanent dipole-permanent dipole attraction means boiling temperatures are close to room temperature

Liquids tht can be easily evaporated or gases that can easily be liquified 

CFCs were used as refrigerants 

Non-flammability, non-toxicity and a suitable boiling temperature are important in making halogenoalkanes suitable for use

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Describe the regulation of halogenoalkanes

They are limited by statutory regulations as they have found to be toxic and damage earth's ozone layer

Damage to ozone layer allows UV light to reach earth and cause skin cancer

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