Haloalkanes

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  • Created by: Heather
  • Created on: 09-03-15 12:45
What is the general formula for a haloalkane?
CnH2n+1X
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What are the four prefixes for each halogen?
Fluoro-, -Chloro-, -bromo- -iodo-
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Haloalkanes have a C-X bond. Why is this bond polar?
As the halogens are more electronegative than carbon so the carbon is delta positive and the halogen is delta negative,
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Describe the polarity of the C-X bond as we go down go down the elements?
They become less polar as we go down Group 7
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Are the haloalkanes soluble and why?
They arent soluble in water as the bonds aren't electronegative enough
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What are the intermolecular forces of attraction in C-X bonds?
-Dipole-dipole attraction, -Van der Waal forces
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Describe the boiling point of haloalkanes as we go down the group and why?
They increase as we go down the halogen group as there is an increase in carbon chain length so an increase in van der Waal forces
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However, what will lower the melting point of the haloalkanes?
If there is an increase in branching of the carbon chain,
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Why do haloalkanes have a higher boiling point than alkanes of a similar chain length?
As 1) they are more polar 2)They have a higher relative molecular mass
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What two factors affect how readily the C-X bond reacts?
The C-X bond polarity, -C-X bond enthalpy
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Why will the C-X bond have delta positive for carbon and delta negative for the halogen?
As X is more electronegative than C so the carbon is electron deficient,
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Which C-X bond would be the most reactive based on bond polarity?
The C-F bond as it is more polar
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For C-X enthalpies, describe their strength as we go down the group and why?
They get weaker as we go down the group as the shared electrons in the C-X bond gets further away from the halogen nucleus so the bond gets weakner
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So, based on bond enthalpies, which C-X bond would be most reactive?
C-I as it has the weakest bonds
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Which factor is more important, and overall, what is the trend of reactivity as we go down the group?
The bond entalphy is a more important factor than bond polarity so reactivity increase as we go down the group,
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What is the definition of a nucleophile?
An ion or group of atoms with a negative charfe that takes part in an organic reaction by attacking an elct
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What are three common nucleophiles?
-Hydroxide ion -:OH, -Ammonia :NH4 -The cyanide ion -:CN
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What do these nucleophiles do in a reaction and what is the reaction called?
They wil each repalce the halogen in a haloalkane, -Nucelophilic substitution,
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WHat is the general equation for nucleophilic substitution?
CH3X + :Nu- = CH3Nu + :X-
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For the reaction with the hydroxide ion, what conditions are used?
-Room temperature, -Ethanol,
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Why is ethanol used and what kind of reaction is it called due to its presence?
Ethanol is used as haloalkanes dont mix with water so used as a solvent -Hydrolysis reaction
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What is the overall reaction of a haloalkane with a nucleophile?
C-X + OH- = COH + X-
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What is the organic product formed?
An alcohol,
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Give an example of this reaction with bromoethane.
C2H5Br + OH- = C2H5OH + Br-
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With a reaction with a cyanide nucleophile, what it the product called?
A nitrile,
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Why is a nucelophilic substitution reaction using a cyanide ion useful?
As the product has one extra carbon in the chain than the starting haloakane which is useful,
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What is the general formula for a haloalkane reacting with ammonia?
C-X + 2NH3 = CNH2 + NH4X
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What are the conditions needed for nucleophilic substitution with ammonia?
-Pressure- Excess concentrated solution of ammonia,
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Why can ammonia still by used as a nucleophile even though it doesnt have a negative charge?
As it has a lone pair of electrons and the nitrogen atoms has a delta negative charge,
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What has to occur to allow ammonia to lose its neutral charge and what is this product called?
A protom ,H+ must be lost to form a primary amine,
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Why is nucleophilic substitution useful?
As it is a way of introducing new functional groups into organic compounds- Haloalkanes can be converted into alcohols, amines and nitriles,
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How are haloalkanes formed and under what conditions?
They are formed when a mixture of an alkane and a halogen are put into bright sunlight,
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What component of the light begins the reaction?
The UV rays of light begin the reaction,
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Give the reaction between hexane and bromine to form a haloalkane and another product.
C6H14(g) + Br2(l) = C6H13Br(l) + HBr(g)
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What is this reaction called?
Free radical substitution,
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What are three stages of this chain reaction?
-Initiation, -Propagation, -Termination,
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What does the first step initiation do?
It break the halogens X-X bond to form two single halodens, 2X
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How does the X-X bond break?
It absorbs the energy of a single quantum of ultraviolet (UV) light which has a greater energy than the X-X bond so it will break,
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Give the equation to show the inititation of Cl2 and include free radicals.
Cl-Cl -Ultraviolet-> 2Cl*
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What does the second step propagation do?
It is the chain part in the reaction where new free radical compunds are made from reacting with another free radical compound
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Give an exmaple of a propagation step using a chlorine free radical and methane.
Cl* + CH4 -> HCl + CH3
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What does the third step termination do?
It removes free radicals by two free radical compunds reacting together to produce a stable compund,
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Give an example of a termination process with two chlorine free radicals.
Cl* + Cl* -> Cl2
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What are CFCs?
Chloroflourocarbons are haloalkanes with no hydrogen atoms,
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Why were CFCs so useful for refridgerants and dry cleaning products?
They are very unreactive under normal conditions so they werent expected to pollute the atmosphere,
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However, waht was the problem with CFCs?
They eventually end up in the atmosphere and decompose to give chlorineatoms which decompose the ozone layer, O3
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Why is the ozone layer important?
It protects the Earth from the harmful exposure of ultraviolet rays which can lead to skin cnacer,
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GIve the equation to show chlorine reacting with the ozone layer.
Cl* + O3 -> ClO* + O2
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Give the equation to show how ClO* formed further reacts with the ozone layer.
ClO* + O3 -> 2O2 + Cl*
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Therefore, what does the chlorine act as the equations?
As a catalyst as the free radical isnt destroyed in the process
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Other cards in this set

Card 2

Front

What are the four prefixes for each halogen?

Back

Fluoro-, -Chloro-, -bromo- -iodo-

Card 3

Front

Haloalkanes have a C-X bond. Why is this bond polar?

Back

Preview of the front of card 3

Card 4

Front

Describe the polarity of the C-X bond as we go down go down the elements?

Back

Preview of the front of card 4

Card 5

Front

Are the haloalkanes soluble and why?

Back

Preview of the front of card 5
View more cards

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