Chemistry AQA AS Unit 2 Haloalkanes

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created on: 02-09-13 13:35
Preview of Chemistry AQA AS Unit 2 Haloalkanes

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Haloalkanes
GENERAL FORMULA
CnH2n+1X
NAMING HALOALKANES
F ­ Fluro
Cl- Chloro
Br- Bromo
I - Iodo
BOND POLARITY
Haloalkanes have a C ­ X bond.
The bond is polar, C + and X ­ as halogens are more electronegative than carbon.
SOLUBILITY
The polar bonds are not polar enough to make the Haloalkanes soluble in water.
Main IMF is dipole-dipole attractions and V.D.W.
BOILING POINT
Increases with increased chain length...
Increases as going down the halogen group...
This is due to increased V.D.W. from increasing no. of electrons.
Increased branching lowers boiling point.
Haloalkanes have higher boiling points than alkanes of similar chain lengths because a) have higher
relative molecular mass b) more polar.
REACTIVITY OF THE C ­ X BOND
The carbon is ELECTRON DEFICIENT.
The halogen is a NUCLEOPHILE (an atom with a partially negative charge that takes part in an
organic reaction by attacking an electron deficient area in another reactant). The halogen attacks the
carbon reagents that are electron rich or have electron rich areas.
RADICAL SUBSTITUTION
FORMATION OF HALOALKANES...
e.g. CH + BR BrCH + HBr (colourless)
SUBSTITUTION: Replacing a group of atoms with another group of atoms.
OBSERVATIONS: Fumes of HBr, and Bromine goes from orange to colourless.
Alkanes are very stable and alkenes are more reactive. So where as alkenes react with Br (aq)
bromine water, alkanes require liquid bromine Br (l) and UV light.
REACTION MECHANISM: It is the name given to a sequence of steps in a reaction.
The reaction of halogens with alkanes is a chain reaction.
Mechanism for this reaction is FREE RADICAL (atom of molecule with
unpaired electron)

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INITIATION STEP:
U/V light for high energy. It breaks the halogens covalent bond.
This is HOMOLYTIC FISSION where the bond is broken evenly
to form 2 free radicals. Each atom acquires one electron from the covalent bond.
PROPAGATION STEP
2 parts that can continue until 1 reaction runs
out.
The halogen atom (radical) can react with either
the alkane or the Haloalkanes produced in their
reactions and therefore a mixture of the
products are made.…read more

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Alkyl Halide Aq NaOH
AgNO (aq) + X (aq) AgX (s) + NO (aq)
Precipitate
MECHANISM: Nucleophilic
HETEROLYTIC FISSION: Uneven breaking of a covalent bond resulting in a positive and negative ion.
CURLY ARROW ­ movement of pair of es
Starts at the lone pair or bond, goes to the symbol.
STEP 1: Nucleophile is attracted to slightly positive C where it donates a pair of electrons to make a
new covalent bond.…read more

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Conditions: Excess ammonia, under pressure.
ELIMINATION REACTION
Removing an atom/group of atoms.
From a haloalkane to an alkene.
Use ethanoic Na/KOH (a solution in
ethanol)
Anhydrous (no water present, only
given as product)
Heat it
Mechanism:
1) The electron pair are withdrawn to Br
2) The Nucleophile donates a lone pair of es to the H on the adjacent C atom.
3) The e pair becomes a part of a C=C double bond.…read more

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