OCR B - halogenoalkanes

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HALOGENOALKANES
It is an alkane with at least one halogen atom in
place of a hydrogen atom.
Naming halogenoalkanes- the prefixes are listed in alphabetical order.
Bonds are PERMANENT-PERMANENT DIPOLE because carbon
and halogen together is a polar molecule. Their boiling points depends
on the size and number of halogen atom present; the bigger the halogen atom and
the more halogen atoms there are higher the boiling point. For e.g. halogenoalkane
with a Cl or Br atom has higher boiling point than F.
BUT
these
larger Halogenoalkanes can cause GREAT ENVIRONMENTAL DAMAGE.
For e.g. chlorofluorocarbons (CFC') are Halogenoalkanes where all the hydrogen
atoms are replaced by chlorine and fluorine atom. They are used for lots of things
because they are very Unreactive. They are used for dry cleaning and degreasing
but this causes damage to the ozone layer.
Key terms
Nucleophile (Nu-) ­ molecule or negatively charged ion with a lone pair of e-s that
it can donate to form a covalent bond (OH-, NH3, H2O, -CN)
Substitution ­ when one group is replaced by another
Mechanism ­ Shows the stages of a reaction
Curly arrows ­ show movement of e-s to make/break bonds
single headed - 1 e-
double headed ­ pair of e-s
CHEMICAL REACTIONS OF HALOGENOALKANES
Reactions of Halogenoalkanes involve breaking C-H bonds. The bond can
break homolytically or heterolytically

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UV) is absorbed by the halogenoalkane. This occurs when
Halogenoalkanes reach the stratosphere, where they are exposed to intense
UV radiation. This is how Cl damages ozone layer
heterolytic fission- this is common under laboratory conditions when
reactions of Halogenoalkanes tend to be carried out in a polar solvent such
as ethanol and water
Reaction condition (Halogenoalkanes are usually hydrolysed
by heating under reflux with NaOH. Often ethanol is added
to act as a solvent) can determine how a bond breaks.…read more

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ORGANIC SYNTHESIS
This involves four stages:-
1. reaction
Things to consider...
Reactants
Solvent
Concentrations
Heat/reflux?
Catalyst?
2. separation
Separating funnel - separates water and aqueous impurities from
product
Anhydrous sodium sulphate - removes final traces of water (can also
use CaSO4 or MgSO4)
3. purification
Final impurities must be
removed by...
Re-crystallisation
Chromatography
Distillation
4.…read more

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Nuclear magnetic resonance (NMR)
Melting point
Volatile liquids (one with low boiling points), these are hard to work with in
reactions. Liquid evaporates before it had a chance to react. You can use reflux
condensers for volatile liquids. The volatile liquid evaporates but then condenses
and drips back into the flask.…read more

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