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Chemistry > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

How are halogenoalkanes classified

A

They are either primary, secondary or tertiary depending on the number of Carbon atoms that the carbon bonded to the halogen is bonded to

Primary 1
Secondary 2
Tertiary 3

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2
Q

What are the products of a free radical substitution mechanism

A

A halogenoalkane and a hydrogen halide

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3
Q

What is step 1 of free radical substitution

A

Initiation

UV light provides energy to break the Cl2 bond the halogen bond

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4
Q

What is step 2 of free radical substitution

A

Propagation (part 1)
The Cl free radical reacts with CH4 to form a CH3 free radical (methyl radical) and HCl

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5
Q

What is step 3 of free radical substitution

A

The CH3 free radical react with chlorine molecules o for, chloromethane and more chlorine free radicals

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6
Q

What is step 4 of free radical substitution

A

Termination
Free radicals react with each other to form stable molecules

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7
Q

How do you write the overall equation for free radical substitution

A

By combining the 2 equations from the propagation stage

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8
Q

What does Ozone do? (3)

A

It reduces the amount of UV radiation that reaches the earth which is useful because too much causes skin cancer, eye damage and possible harm to crops

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9
Q

What destroys the Ozone

A

Chemicals called CFC’s (chlorofluorocarbons)

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10
Q

What are 3 properties of chlorofluorocarbons

A

Less reactive than alkanes since C-F bond is so strong

They diffuse into the upper atmosphere unchanged

Under the influence of intense ultraviolet radiation in the stratosphere they decompose to from radicals

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11
Q

Describe the chemical reaction between Ozone and CFC’s
(5)

A

UV causes chlorine atom to break away from CFC molecule

The free chlorine atom hits an Ozone molecule

The chlorine atom pulls one Oxygen atom away

A free oxygen atoms hits the chlorine monoxide molecule

Another free radical chlorine atom is formed

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12
Q

What does chlorine acts as in the breakdown of Ozone

A

A catalyst as its not used up in the reaction and is regenerated
It also is not shown in the overall equation

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13
Q

What are safer alternatives to CFC’s and why are they safer alternatives

A

Hydrochlorofluorocarbons (HCFC)
Hydrofluorocarbons (HFC)

They are safer because the C-F bond us stronger than the C-H bond so they can’t produce free radicals as ,Amy break down before even reaching the stratosphere

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14
Q

How have aerosols been made safer

A

They use pump spray systems or use nitrogen as the propellant

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15
Q

How have industrial fridges been made safer

A

They use ammonia or hydrocarbons as the coolant gas

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16
Q

How are foamed polymers made safely

A

They use carbon dioxide or pentane to make them

17
Q

What are nucleophiles

A

They are lone pair donors to electron deficient carbons / species

18
Q

When hydroxide ions are the nucleophile, what is they reagent and the condition

A

Potassium hydroxide

Warm aqueous solvent

19
Q

When cyanide ions are the nucleophile in nucleophilic substitution, what is the reagent and the conditions

A

Potassium cyanide CN-

Ethanol solvent

20
Q

When ammonia is the nucleophile in nucleophilic substitution, what is the reagent and the conditions

A

Ammonia is reagent

Excss ammonia in a warm ethanol solvent in a sealed tube

21
Q

Why is excess ammonia used in nucleophilic substitution when used as a nucleophile

A

Because it forms prpan -1- amine which also has a lone pair and can therefore act as a nucleophile and react with unreacted halogenoalkanes the excess ammonia minimises further substitutions from occurring

22
Q

What 2 factors affect how easily the carbon-halogen bond breaks/ the reactivity halogenoalaknes in terms of nucleophilic substitution and which one is the more important factor

A

The Polarity of the carbon-halogen bond (more polar means easily attacked by nucleophiles)

The strength of tye carbon halogen bond (weaker bond means breaks easier and is more reactive)

More important is the bond enthalpy as experiments show reactivity increases down the halogen group

23
Q

What are the products when halogenoalkanes undergo elimination reactions (3)

A

Alkenes
Water
A salt

24
Q

What reaction conditions favour elimination (3)

A

Ethanolic solvent

Higher temperatures

Increased branching

25
Q

What reaction conditions favourite substitution

A

Aqueous solvent

Lower temperatures

Little / No branching

26
Q

What does the hydroxide ion act as in elimination reactions and why
What must you remember when outlining elimination mechanisms

A

A base because it’s dissolved in ethanol

The hydrogen us removed from the carbon next to a carbon bonded to the halogen

27
Q

What happens if the carbon chain length is 4 or more in terms of elimination

A

A mixture of positional isomers may be formed when it undergoes elimination reactions

Chemistry (23 decks)

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