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Organic Chemistry > Haloalkanes > Flashcards

Haloalkanes Flashcards

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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

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

A

Reagents: NaOH
Conditions: warm, aqueous

24
Q

Are haloalkanes polar?

A

Yes

25
Q

Give reagents and conditions for nucleophilic addition to form nitriles

How does this affect the C chain

A

KCN
Aqueous ethanol

(CN- adds an extra carbon to the chain)

26
Q

Name CH3CH(CN)CH3

A

2-methyl propane nitrile

27
Q

Give reagents and conditions for nucleophilic addition to form primary amines

A

Excess NH3

28
Q

Why is excess NH3 used to form primary amines

A

To avoid further substitution

29
Q

How can RNH2 act as a nucleophile?

A

There is a lone pair on N

30
Q

How to get a high yield of quaternary ammonium salt

A

Use a large excess of haloalkane

31
Q

What are quaternary ammonium salts used for?

A

Hair products

32
Q

What is the basic structure of a quaternary ammonium salt?

A

A N+ surrounded by 4 carbon chains

33
Q

3 rules for forming quaternary ammonium salts

A

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
Q

Give the reagents and conditions for elimination

A

NaOH

hot, in ethanol

35
Q

What is the role of NaOH or OH- ions in elimination?

A

As a base (they accept H+)

36
Q

What are the 3 stages of elimination?

A

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
Q

When naming an alkene what must you always check for?

A

E-Z isomerism

38
Q

If the alkene product of elimination shows geometrical isomerism, which isomers will be formed?

A

Both E and Z

39
Q

Do primary haloalkanes favour elimination or substitution?

A

Substitution

40
Q

Do secondary haloalkanes favour elimination or substitution?

A

Both

41
Q

Do tertiary haloalkanes favour elimination or substitution?

A

Elimination

42
Q

How does the strength of the base affect the chances of elimination?

A

As the strength of the base increases the chances of elimination increase

43
Q

What is a CFC

A

A chlorofluorocarbon

44
Q

Do CFCs usually contain Hydrogen

A

No

45
Q

What state are shirt chain CFCs usually in?

What are long chain ones used for?

A

Gaseous, used in refrigerators

Dry cleaning and degreasing solvents

46
Q

Why is O3 important?

A

Absorbs UV radiation which causes cancer

47
Q

Why are CFCs bad?

A

In UV light Cl• are produced which decompose O3

48
Q

What is the overall equation to show ozone break down?

A

2O3 —> 3O2

49
Q

Why can we say Cl• is a catalyst?

A

It is not destroyed and is regenerated

50
Q

Give the 2 propagation steps of Cl• decomposing O3

A

Cl• + O3 —> ClO• + O2

ClO• + O3 —> 2O2 + Cl•

51
Q

Why are CFC alternatives safer?

A

They do not contain Cl atoms so no Cl• can be produced

Or

They will break down before they reach the ozone layer

52
Q

Why is the ozone layer important

A

It absorbs harmful UV radiation which can cause cancer by damaging DNA in skins cells

53
Q

Why can we say Cl• is a catalyst

A

It is regenerated

Organic Chemistry (12 decks)

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