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AQA A-Level Organic Chemistry > 3.3 Halogenoalkanes > Flashcards

3.3 Halogenoalkanes Flashcards

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1
Q

What is a halogenoalkane?

A

Compounds which one or more hydrogen atoms in an alkane have been replaced by halogen atoms

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2
Q

What are the halogen prefixes?

A

Fluoro
Chloro
Bromo
Iodo

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3
Q

What are some nomenclature rules for halogenoalkanes?

A

The different halogens are listed alphabetically

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4
Q

What are some uses for halogenoalkanes?

A 
Refrigerator
Solvents
Anaesthetics
Aerosol propellants 
Insecticides
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5
Q

What is a primary, secondary and tertiary structure?

A

Primary- only has 1 other carbon attached to the carbon with the halogen attached

Secondary- has 2 carbons attached to the carbon with the halogen attached

Tertiary - has 3 carbons attached to the carbon with the halogen attached

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6
Q

What is the ozone layer?

A

O3 forms naturally in the atmosphere

It protects us from harmful UV radiation

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7
Q

What affects the ozone layer?

A

CFC’s - Chlorofluorocarbons

They form holes in the layer

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8
Q

What are used instead of CFC’s?

A

HFC’s - Hydrofluorocarbons

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9
Q

What happens when CFC’s reach the ozone layer?

A

Chlorine free radicals are formed when CFC’s are exposed to UV radiation

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10
Q

What reaction shows what happens to the ozone layer? Type of reaction?

A

O3 + Cl• -> ClO• + O2
ClO• + O3 -> 2O2 + Cl•

Chain reaction

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11
Q

Name the types of reactions that can take place with halogenoalkanes?

A

Free radical substitution
Nucleophilic substitution
Elimination

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12
Q

What is free radical substitution?

A

A chain reaction

Where one thing replaces another with 3 stages

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13
Q

What are the three stages of free radical substitution?

A

Initiation
Propagation
Termination

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14
Q

What is the initiation mechanism?

A

Cl2 ——> 2Cl•

With UV light over the arrow

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15
Q

What takes place in initiation?

A

Homolytic bond fission

When the bond breaks each atom takes an electron from the bond now called free radicals

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16
Q

What is meant by propagation step?

A

Where free radicals are used up and then regenerated

17
Q

What is the mechanism for propagation in free radical substitution? (Use CH4 and Cl)

A

CH4 + Cl• -> •CH3 + HCl

•CH3 + Cl2 -> CH3Cl + Cl•

18
Q

What is the mechanism for termination in free radical substitution? (Use CH4 and Cl)

A

Cl• + Cl• -> Cl2
•CH3 + Cl• -> CH3Cl
•CH3 + •CH3 -> C2H6

19
Q

In free radical substitution how can you make sure you get more of one particular product?

A

Use an excess of the reactant that will help produce more of the product

Therefore collisions are more likely between the one in excess and the other free radical

20
Q

What are the strongest to weakest bonds of carbon-halogens?

A 
Strongest 
C-F
C-Cl
C-Br
C-I
Weakest
21
Q

What is a nucleophile? What do they do?

A

Attracts positive charge

Attack a halogenoalkane and form a bond with it
As the carbon will have a delta + charge therefore the nucleophile will be attracted to it

22
Q

Examples of a nucleophile?

A

:OH- (hydroxide ion)
:NH3 (ammonia)
:CN- (cyanide ion)

23
Q

How do you know it’s likely nucleophilic substitution?

A

A polar molecule - nucleophilic

Saturated - substitution

24
Q

How does carbon-halogen bonds affect reactions?

A

The weaker the carbon-halogen bond the more reactive it will be

25
Q

In nucleophilic substitution how does a nucleophile react with a halogenoalkane? (Where do the arrows go)

A

From the lone pair of the nucleophile to the carbon

From the middle of the carbon halogen bond to the halogen

26
Q

In nucleophilic substitution what does the arrow from the middle of the carbon to the halogen show?

A

Shows the electrons that were in the bond but now broken they go to the carbon

27
Q

What are the products in nucleophilic substitution?

A

The nucleophile attached to the alkane
And
A free radical halogen

28
Q

What are the arrows of nucleophilic substitution if the reaction requires two steps? (Ammonia)

A

The arrow goes from the middle of the hydrogen/nitrogen bond on to the nitrogen

The arrow goes from the ammonia free radical to the hydrogen

29
Q

What are the final products in nucleophilic substitution of a halogenoalkane and ammonia?

A

The alkane with NH2 attached
Ammonium ion
The halogen free radical

30
Q

What is produced in the nucleophilic substitution of a halogenoalkane and ammonia in the first step?

A

An unstable intermediate that has to lose something in order to become a stable molecule

An alkane with NH3 attached

31
Q

What are the conditions for nucleophilic substitution?

A

In water or aqueous solution
Using ethanol to enable the reactants to mix together
Low temperature

32
Q

What are nucleophilic reactions useful for making?

A

Alcohols
Nitriles
Amines

Used for drugs in medicine

33
Q

What is used to heat any organic chemicals?

A

Reflux apparatus

34
Q

What is used in reflux apparatus?

A

A condenser

To prevent the liquid from evaporating therefore you have product to collect

35
Q

What is an elimination reaction?

A

A reaction between a halogenoalkane and an OH- ion

Something is lost and nothing is gained

36
Q

Where do the arrows go in elimination reactions?

A

From the :OH- to the hydrogen

From the middle of the c-h bond you drew the other arrow to - to the middle of the c-c bond

From the middle of the carbon-halogen bond to the halogen

37
Q

What is produced in elimination reactions?

A

An alkene
Water
A halogen free radical

38
Q

What conditions do elimination reactions need?

A

Ethanolic conditions and high temperature

AQA A-Level Organic Chemistry (14 decks)

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