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Organic Chemistry > Haloalkanes > Flashcards

Haloalkanes Flashcards

(53 cards)

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1
Q

What mechanism is used to form haloalkanes

A

Free radical substitution

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2
Q

Conditions for radical substitution

A

UV light

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3
Q

What does free radical substitution produce

A

A haloalkane and a hydrogen halide

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4
Q

What are the 4 stages of free radical substitution?

A

Initiation
1st propagation
2nd propagation
Termination

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5
Q

What is a free radical?

A

A very reactive species with an impaired molecule

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6
Q

Describe initiation

A

X-X bonds are weaker than C-H bonds so are broken first
UV light causes covalent bond to break between halogen molecules, creating 2 halogen radicals

X2 —> 2X•

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7
Q

Equation for CH4 in first propagation stage of free radical substitution

A

CH4+X• —> •CH3 + HX

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8
Q

Equation for CH4 in second propagation stage of free radical substitution

A

•CH3 + X2 —> CH3X + X•

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9
Q

There is a chain of first and second propagations. When does this chain end?

A

Once you run out of halogen molecules or alkanes

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10
Q

What is termination?

A

The remaining unstable species combining to make neutral molecules

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11
Q

What are the 3 possible termination steps?

A

X•+X• —> X2

  • CH3 + X• —> CH3X
  • CH3 + •CH3 —> CH3CH3
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12
Q

What is the alkyl radical from CH4?

A

•CH3

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13
Q

What happens if an excess of the halogen is added to a free radical substitution?

A

Further substitution is possible, leading to the formation of CH2X2, CHX3, or CCl4

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14
Q

How can you reduce the chance of further substitution?

A

Using an excess of the alkanes

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15
Q

What do curly arrows represent?

A

The movement of an electron pair

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16
Q

Where must curly arrows always start?

A

At a bond or a lone electron pair

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17
Q

Define nucleophile

A

A species that donates a lone pair of electrons

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18
Q

Define Electrophile

A

Accepts a lone pair of electrons

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19
Q

What a carbon - halogen bonds?

A

Polar

The halogen has a greater electronegativity so is delta negative
The C is delta positive

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20
Q

Why is the C readily attacked by a nucleophile?

A

The C is delta positive

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21
Q

Describe the 3 steps of nucleophilic substitution

A

Lone pair of nucleophile forms a Covalent bond with delta positive C atom

Electrons on C-halogen bond move onto halogen atom, breaking the C-X bond, and forms a halide ion

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22
Q

Order C- halogen bonds from strongest to weakest

Comment on the reactivity

Study These Flashcards
A

C-F
C-Cl
C- Br
C- I

Reactivity increases as you go down the group

23
Q

Give reagents and conditions for nucleophilic addition to form alcohols

Study These Flashcards
A

Reagents: NaOH
Conditions: warm, aqueous

24
Q

Are haloalkanes polar?

25
Give reagents and conditions for nucleophilic addition to form nitriles How does this affect the C chain
KCN Aqueous ethanol (CN- adds an extra carbon to the chain)
26
Name CH3CH(CN)CH3
2-methyl propane nitrile
27
Give reagents and conditions for nucleophilic addition to form primary amines
Excess NH3
28
Why is excess NH3 used to form primary amines
To avoid further substitution
29
How can RNH2 act as a nucleophile?
There is a lone pair on N
30
How to get a high yield of quaternary ammonium salt
Use a large excess of haloalkane
31
What are quaternary ammonium salts used for?
Hair products
32
What is the basic structure of a quaternary ammonium salt?
A N+ surrounded by 4 carbon chains
33
3 rules for forming quaternary ammonium salts
Any C chains on the N at the start of he reaction will remain on the N All Hs directly bonded to the N are removed A halide ion from the haloalkane will also be produced
34
Give the reagents and conditions for elimination
NaOH | hot, in ethanol
35
What is the role of NaOH or OH- ions in elimination?
As a base (they accept H+)
36
What are the 3 stages of elimination?
1: OH- removes a H atom from an adjacent C to the halogen atom 2: the e- in the C-H bond move into the C-C bond to create a C=C bond 3: e- in the C-halogen bond move onto the halogen atom, breaking the bond and creating a halide ion
37
When naming an alkene what must you always check for?
E-Z isomerism
38
If the alkene product of elimination shows geometrical isomerism, which isomers will be formed?
Both E and Z
39
Do primary haloalkanes favour elimination or substitution?
Substitution
40
Do secondary haloalkanes favour elimination or substitution?
Both
41
Do tertiary haloalkanes favour elimination or substitution?
Elimination
42
How does the strength of the base affect the chances of elimination?
As the strength of the base increases the chances of elimination increase
43
What is a CFC
A chlorofluorocarbon
44
Do CFCs usually contain Hydrogen
No
45
What state are shirt chain CFCs usually in? What are long chain ones used for?
Gaseous, used in refrigerators Dry cleaning and degreasing solvents
46
Why is O3 important?
Absorbs UV radiation which causes cancer
47
Why are CFCs bad?
In UV light Cl• are produced which decompose O3
48
What is the overall equation to show ozone break down?
2O3 —> 3O2
49
Why can we say Cl• is a catalyst?
It is not destroyed and is regenerated
50
Give the 2 propagation steps of Cl• decomposing O3
Cl• + O3 —> ClO• + O2 ClO• + O3 —> 2O2 + Cl•
51
Why are CFC alternatives safer?
They do not contain Cl atoms so no Cl• can be produced Or They will break down before they reach the ozone layer
52
Why is the ozone layer important
It absorbs harmful UV radiation which can cause cancer by damaging DNA in skins cells
53
Why can we say Cl• is a catalyst
It is regenerated

Organic Chemistry (12 decks)

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