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Chemistry > 3.3.3 - Haloalkenes > Flashcards

3.3.3 - Haloalkenes Flashcards

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1
Q

What are three types of attackers

A

Nucleophile

Electrophile

Free radicals

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2
Q

Explain what a nucleophile is, what it attacks and examples

A

Posses a lone pair of electrons (with which to form a bond )

Attack positive and delta positive

Examples :OH- , :CN- , :NH3

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3
Q

Explain what a electrophile is, what it attacks and example

A

Electron deficient short of electrons therefore has a positive charge or delta positive

Attacks electron rich areas (e.g. C=C)

Examples H+ , H delta +

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4
Q

Explain what free radicals are, what they attack and examples

A

Has an unpaired electron (very reactive )

Attacks everything e.g. C-C

Examples Cl• , Br•, •CH3

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5
Q

Describe single , non-polar bonds

A

No delta + or delta -
Therefore only attacked by free radicals

Eg alkanes

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6
Q

Describe single , polar bonds

A

An electronegative element causes C delta + therefore attacked by nucleophiles

Eg haloalkanes

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7
Q

Describe double bonds

A

C=C contains electron rich area therefore attacked by electrophile

Eg alkenes

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8
Q

Three types of reactions

A

Substitution
Elimination
Addition

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9
Q

Explain substitution

A

Single bonds one atom or a number of atoms is replaced by another

C-X +Y – C-Y + X

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10
Q

Explain elimination

A

Single bonds small molecules is removed from a larger molecule a single bond becomes a double bond.

XC-CY – C=C + XY

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11
Q

Explain addition

A

Double bonds a molecule is added to a molecule with double bonds a double bind becomes a single bond

C=C + XY – XC=CY

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12
Q

What do curly arrows represent

A

Movement of electron pairs

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13
Q

Why are haloalkanes attacked by nucleophiles

A

Halogen atoms are more electronegative than C so C become delta positive

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14
Q

What conditions are needed for NaOH to nucleophiliclly substitute a haloalkanes

A

Warm , aqueous

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15
Q

Nucleophilic substitution What happens when NaOH reacts

A

Replaced the halogen with OH group and produces a NaX compound

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16
Q

Nucleophilic substitution what condition are needed for KCN

A

Ethanolic, warm

17
Q

Nucleophilic substitution what happens when KCN reacts

A

Replaces halogen with CN group makes a nitrile and KX

18
Q

Nucleophilic substitution what conditions are needed for NH3 to react with haloalkane

A

Excess in ethanol and high pressure

19
Q

Nucleophilic substitution what happens when NH3 reacts with haloalkane

A

NH3 replaces halogen then further on it becomes NH2 which makes an amine

20
Q

How do you stop further substitution occurring in nucleophilic substitution with NH3

A

Use excess NH3

21
Q

What conditions are needed for a elimination reaction with NaOH

A

Alcoholic and reflux in alcoholic solution

22
Q

What happens in elimination when alcoholic NaOH is used

A

Removes a H atom and a halogen atom makes an alkene

23
Q

Why does the NaOH have to be alcoholic to make elimination occur

A

In alcohol the :OH- acts as a base and picks up protons

24
Q

Show diagram of elimination of haloalkanes

A 
|     | 
- C -  C -
    |     | 
    H   X 
   /
  /
OH
25
Q

What is initiation in radical reaction mechanisms

A

Molecules are exposed to UV light breaks apart to make radicals

26
Q

What happens in propagation of radical reaction mechanisms

A

Step 1
Alkane/Haloalkane + Haloradical makes a carbon radical and a HF (etc)

Step 2
Carbon radical + halomolecule make alkane haloalkane + haloradical

27
Q

What happens in the termination stage of radical reactions

A

Radicals react with each other to form stable compounds

28
Q

What is the ozone layer and what does it do

A

O3 formed naturally in upper atmosphere

Absorbs harmful UV radiation

29
Q

What are CFC’s

There decomposing characteristics

A

Chlorofluorocarbons
Very unreactive
Reach ozone layer before decomposing

30
Q

What has research showed us about CFCs

A

As we started using CFCs the ozone has depleted

31
Q

Alternative to CFC’s

A

HCFCs
Degrade before atmosphere

HFC
No Cl so no ozone depletion potential

32
Q

What is the mechanism that causes ozone depletion

A

Free radical substitution

33
Q

What is the initiation step for breaking down the ozone

A

C-Cl bonds are weakest bonds in compound so are broken

UV radiation homolytically produces free radicals

CF3Cl —- CF3 +•Cl

34
Q

What are the propagation steps of ozone depletion

A

Chlorine radicals react with O3 to make ClO radicals and oxygen molecules

O3 + •Cl —- ClO• + O2

Chlorine radicals then react with O3 to produce oxygen and chlorine radicals

ClO• + O3 —- 2O2 + Cl•

35
Q

What is the termination step of ozone depletion

A

Eventually 2 radicals react with each other which will stop the reaction

Cl•+Cl• —- Cl2

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