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A Level Chemistry > 3.3.3 Halogenoalkanes > Flashcards

3.3.3 Halogenoalkanes Flashcards

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1
Q

Why do halogenoalkanes contain polar bonds?

A

Halogen is > electroneg. than C.

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2
Q

What does a halogenoalkane being polar cause the C to be and what happens to it as a result?

A

Carbon becomes slightly e- deficient and will regularly be attacked by nucleophiles and the halogen is lost.

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3
Q

What is a nucleophile?

A

A molecule/ion with a lone pair of e-s that are attracted to the e- deficient carbon atom.

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4
Q

What usually results when a nucleophile attacks a C?

A

Replacement of an atom> group of atoms usually attached to the C.

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5
Q

What are the three nucleophiles we need to know?

A

OH- (with dots), CN- (with dots), NH3 (with dots).

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6
Q

Under what conditions do halogenoalkanes undergo nucleophilic substitution with OH-? What is formed?

A

Halogenoalkanes are warmed with aqueous sodium hydroxide or potassium hydroxide to form an alcohol.

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7
Q

What do the arrows in the mechanism have to touch?

A

The letter and the lone pair.

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8
Q

In a nucleophilic substitution with OH- what happens to the C-X(halogen) bond?

A

C-X is polar so the C δ+ attracts a lone pair of e-s from the OH- ion.

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9
Q

What happens to the C-X bond after the C δ+ attracts a lone pair? What is formed?

A

Br takes both e-s and a new bond between the C and the OH- forms, making an alcohol.

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10
Q

What happens to the C-X bond after the C δ+ attracts a lone pair? What is formed?

A

Br takes both e-s and a new bond between the C and the OH- forms, making an alcohol.

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11
Q

Under what conditions do halogenoalkanes undergo nucleophilic substitution with CN-? What is formed?

A

Halogenoalkanes are warmed with an alcoholic solution of potassium cyanide to form a nitrile.

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12
Q

Do all nucleophilic substitutions follow the same procedure?

A

Yes but with different ions.

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13
Q

Under what conditions do halogenoalkanes undergo nucleophilic substitution with NH3? What is formed?

A

Halogenoalkanes are warmed with an excess of ammonia in a sealed container to form a primary amine.

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14
Q

If the hydroxide is aqueous what does it act as and what is formed and how is it formed?

A

A nucleophile, forms an alcohol by nucleophilic substitution.

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15
Q

What can the hydroxide also act as? What does it do and how by? What does it form?

A

A base, removing a H and a halogen by an elimination reaction. Forms an alkene.

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16
Q

How can we tell if it’s an elimination rection?

A

Higher temp. and ethanol.

17
Q

How can we tell if it’s a substitution reaction?

A

Lower temperature and aqueous.

18
Q

What does CFC stand for?

A

Chlorofluorocarbon.

19
Q

What is a CFC?

A

A hydrocarbon where all the Hs have been subbed by both F and Cl.

20
Q

Why are CFCs very unreactive?

A

The bonding between C-F and C-Cl is very strong, making them unreactive.

21
Q

What is the molecular formula of ozone?

A

O3.

22
Q

What is ozone to oxygen?

A

An allotrope.

23
Q

Why is ozone destruction blamed on CFCs that make their way into the stratosphere?

A

Because they react with UV light (from the sun) to form very reactive Cl radicals, chemical reactions between the Cl radicals and ozone convert ozone gas to oxygen gas.

24
Q

What is the reaction for O and UV light?

A

O2 -> O• + O•

25
Q

How do O and O• react?

A

O2 + O• -> O3

26
Q

How does ozone and UV light react?

A

O3 -> O2 + O•

27
Q

What radicals destroy ozone?

A

Cl and Br.

28
Q

What are the propagation steps for Cl• reacting with O3?

A

Cl• + O3 -> ClO• + O2

ClO• + O3 -> 2O2 + Cl•

29
Q

What is the overall reaction for Cl•s reacting with O3?

A

2O3 -> 3O2, chlorine cancels out.

30
Q

What is replacing CFCs?

A

HCFCs/

31
Q

What does HCFC stand for?

A

Hydrochlorofluorocarbons.

32
Q

What do HCFCs contain?

A

A C-H bond.

33
Q

What makes HCFCs not destroy ozone?

A

Easily attacked by OH radicals in the lower atmosphere (troposphere), the products dissolve in the water and end up as rain so they don’t reach the stratosphere.

34
Q

What are uses of halogenoalkanes and what do they produce?

A

Anaesthetics, aerosol, solvents, refrigerants, insecticides. CFCs.

35
Q

How do you tell the difference between nucleophilic sub and electrophilic add?

A

Nucleophilic sub always involves a halogenoalkane, electrophilic add always involves an alkene.

36
Q

Explain why a cyclic structure is a weaker base.

A

Lone pair on N, spread into a ring, less available for donation.

A Level Chemistry (26 decks)

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