4.5 Haloalkanes Flashcards

1
Q

What are haloalkanes ?

A

Haloalkanes are compounds containing carbon, hydrogen and at least 1 halogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are aliphatic haloalkanes ?

A

Halogen joined to a straight chain or branched carbon chain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a primary haloalkane ?

A

0/1 alkyl groups attached to carbon with halogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a secondary haloalkane ?

A

2 alkyl groups attached to the carbon atom with halogen attached.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a tertiary haloalkane ?

A

3 alkyl groups attached to carbon atom with halogen attached.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What type of bond is the halogen-carbon bond in a haloalkane ?

A

Polar bond are halogens are more electronegative than carbon so pair of electrons in the bond are closer to the halogen than the carbon.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why can carbon atom attract a nucleophile in haloalkane ?

A

Carbon has slight positive charge so attracts nucleophile, that acts as an electron pair donor.
Eg., OH-, H20, NH3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a nucleophile ?

A

A chemical species that can donate a pair of electrons to a different chemical species (generally to an electrophile) to form a chemical bond in a reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is nucleophilic substitution of haloalkanes ?

A

When primary haloalkanes react with a nucleophile in a substitution reaction, where the halogen is substituted for the nucleophile.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is hydrolysis of haloalkanes ?

A

Chemical reaction involving water or an aqueous solution that causes the braking of a bond in a molecule.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the first step in nucleophilic substitution ?

A

Nucleophile approaches carbon atom attached to the halogen from the opposite side of the molecule.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is minimised by the direction of attack in nucleophilic substitution ?

A

Minimises repulsion between nucleophile and delta negative halogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is attracted to carbon atom in nucleophilic substitution ?

A

Lone pair of electrons is attracted and donated to the delta positive carbon atom attached to the halogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What occurs when attraction is formed between lone pair of electrons and carbon atom of haloalkane ?

A

-Carbon-halogen bond is broken by heterolytic fission.
-New bond is formed between oxygen, from nucleophile, and carbon atom on haloalkane.
This forms new organic product, an alcohol, and a halide ion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the rate of hydrolysis determined by in a haloalkane ?

A

Depends on strength of carbon-halogen bond in haloalkane.
C-F bond is strongest
C-I bond is weakest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is rate of hydrolysis determined by bond strength in haloalkane ?

A

Less energy is requires to break weaker bonds so rate of hydrolysis is quicker.

17
Q

How do you measure rate of hydrolysis ?

A

The rate can be followed by presence of aqueous silver nitrate. As reaction takes place, halide ions are produced, which react with Ag+ to form a precipitate of a silver halide.

18
Q

Why are haloalkanes insoluble in water ?

A

They are unable to form hydrogen bonds with water, despite have polar bonds. Therefore, an ethanol solent is used in hydrolysis as it allows haloalkane to dissolve and mix with water to produce a precipitate.

19
Q

What is the property of boiling points of haloalkanes compared to their alkane counterparts ?

A

Higher boiling points due to increased London forces.

20
Q

What is the flammability of haloalkanes compared to their alkane counterparts ?

A

Less flammable due to fewer C-H bonds.

21
Q

Where are haloalkanes used ?

A

Used in electronic industry as a flame retardant (BFR’s).
CFC’s were used in refrigerators and air conditioning units, but now HFC’s are used for refrigerators.

22
Q

Where is the ozone layer ?

A

At the edge of the stratosphere, which is above the troposphere (lowest part of Earth’s atmosphere).

23
Q

What is stratospheric ozone ?

A

‘Good’ ozone as in this level, it acts to block UV radiation from the sun.

24
Q

What is tropospheric ozone ?

A

‘Bad’ ozone as this acts as a harmful pollutant to humans, animals and the environment due to it being close to Earth’s surface.

25
Q

Why are CFC’s stable ?

A

Stable due to carbon-halogen bond strength

26
Q

When do CFC’s remain stable until ?

A

Remain stable until they have reached the stratosphere, where they begin to break down, which forms chlorine radicals, which then react with ozone catalysing ozone depletion.

27
Q

Why is UV radiation bad when CFC’s reach the stratosphere ?

A

UV radiation provides enough energy to break the carbon-halogen bond by homolytic fission, so carbon-chlorine bond is broken.

28
Q

What is another ozone depletion reaction?

A

Nitrogen oxide also catalyses the breakdown of ozone as nitrogen oxide radicals are formed naturally during lightening strikes.