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Chemistry - Module 4 > 15 - Haloalkanes > Flashcards

15 - Haloalkanes Flashcards

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1
Q

Define nucleophile

A

electron pair donor

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2
Q

Examples of nucleophiles

A

Hydroxide ions / water molecules / ammonia molecules

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3
Q

How are haloalkanes classifies

A

Same as alcohols = primary/secondary/tertiary

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4
Q

How do haloalkanes react

A

Nucleophilic Substitution

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5
Q

Why are haloalkanes reactive

A

• Halogens more reactive than carbons = polar bond
• Carbon = slightly positive so can attract species with lone pairs
• When a haloalkane reacts with a nucleophile, the nucleophile replaces the halogen in a substitution reaction = NUCLEOPHILLIC SUBSTITUTION

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6
Q

Define hydrolysis

A

involves water or aqueous solution of a hydroxide.

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7
Q

Product of hydrolysis of haloalkanes

A

Alcohols + sodium halide

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8
Q

Conditions for hydrolysis of haloalkanes

A

aqueous sodium hydroxide, heated under reflux (

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9
Q

Why do we heat under reflux

A

Reaction slow at room temp

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10
Q

Equation for 1-bromobutane reacting with sodium hydroxide

A

.1-bromobutane + NaOH -> butan-1-ol + NaBr

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11
Q

What type of haloalkane does nucleophilic substitution work on

A

Primary

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12
Q

How to draw nucleophilic substitution mechanism

A

• Only need to show the OH ion
• Draw dipole between C-X (halogens are more electronegative than C)
• Curly arrow from lone pair on OH- to C𝛅+
• Curly arrow from C-X bond to X
• Draw final product and the X- ion

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13
Q

Draw the mechanism for 1-bromoethane reacting with sodium hydroxide

A
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14
Q

What does the rate of hydrolysis depend on

A

C-X bond strength

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15
Q

Strengths of all relative bonds

A

• C-F = very strong bond = unreactive
• C-Cl = strong bond = relatively unreactive
• C-Br = weaker bond = reacts faster
• C-I = weakest bond = reacts even faster

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16
Q

Does the rate of hydrolysis increase or decrease as c-x bind strength increases

A

Decreases

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17
Q

Why does the rate of hydrolysis increases as the C-X bond strength decrease

A

as less energy is required to break the C-X bond.

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18
Q

How to measure the rate of hydrolysis in primary haloalkanes

A

• Undergo the reaction with aqueous silver nitrate
- add ethanol

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19
Q

What acts as the nucleophile in the reaction with aqueous silver nitrate

A

o water (from the nitrate) acts as a nucleophile

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20
Q

Why do we add ethanol

A

• Haloalkanes are insoluble in water = Need ethanol (solvent) to allow the water and haloalkane to mix (prevents the mixture from separating into two layers)

21
Q

What would we see in the reaction with silver nitrate

A

silver halide precipitate forms
• Ag+(aq) + X-(aq) = > AgX(s)

22
Q

Colours if precipitates

A

• Chlorine = white
• Bromine = cream
• Iodine = yellow

23
Q

Which precipitate forms more quickly

A

The yellow precipitate will form the fastest - Idiome

24
Q

Why would the yellow precipitate form the fastest

A

because the C-I bond has the lowest bond enthalpy, so it is the easiest to break and will cause the I- ions to form the fastest

25
Q

Strength of c-x bond not only factor effecting rate of hydrolysis?

A

Structural isomers

26
Q

Do Tertiary haloalkanes more readily accept OH - ion

A

Yes = because more stable than primary

27
Q

How does the c-x bond break

A

heterolytic fission

28
Q

Draw the mechanism for 2-chloro-2-methyl propane

A
29
Q

Define organohalogen

A

at least one halogen atom joined to carbon chain

30
Q

Uses of organohalogen

A

General solvents, dry cleaning solvents, making polymers, flame retardants, refrigerants, pesticides

31
Q

Why have they become a focus of concern

A

• Unnatural and not broken down by environment

32
Q

Where is the ozone layer found

A

in the outer edge of the stratosphere

33
Q

• Only a tiny fraction of gases making up the ozone layer is

A

ozone (O3)

34
Q

Function of ozone gas

A

absorbs most of the UV-B from sun

35
Q

What is UV-B

A

biologically damaging, causes sunburn

36
Q

Therefore, why is the depletion of the ozone layer dangerous

A

More UV-B = could lead to increased genetic damage and/or an increased risk of skin cancer.

37
Q

R/s between ozone + UV

A

• Ozone is continually formed and broken down by UV

38
Q

Equation for ozone continually being formed and broken down by UV

A

• O = RADICAL

THIS IS NORMAL

39
Q

Initially, what breaks down to get the O radical

A

high energy UV O2 -> 2O

THIS IS NORMAL

40
Q

What are CFC’s

A

are very stable as C-X bond is strong

41
Q

CFC’s remain stable until..

A

they reach the stratosphere

42
Q

What happens when the CFC come into con tact with UV

A

• UV radiation provides enough energy to break C-X bond by homolytic fission

43
Q

What forms after the C-X bond is broken by homolytic fission

A

Chlorine radicals

44
Q

Effect of chlorine radicals = catalyse break down of ozone layer

A
45
Q

Initial step

A

• Photodissociation – triggered by UV radiation
• CF2Cl2 -> CF2Cl∙ + Cl∙
• C-Cl bond has lowest enthalpy thus is the bond that breaks

46
Q

Propagation step

A

• Very reactive Cl∙ reacts with ozone in 2 step process:
• Cl∙ + O3 -> ClO∙ + O2
• ClO∙ + O -> Cl∙ + O2
• OVERALL: O3 + O ->2O2
• This repeats in a cycle = chain reaction.

47
Q

Effect of nitrogen oxide

A

oxide radicals (NO∙) are formed naturally during lightning strikes and from aircraft travel in stratosphere
• Breakdown of ozone is similar reaction to chlorine radicals

48
Q

Probation step with nitrogen oxide

A
  • NO∙ + O3 -> NO2∙ + O2
  • NO2∙ + O -> NO∙ + O2
  • OVERALL: O3 + O -> 2O2
49
Q

why are oxygen radicals called diradicals

A

each atom has 2 unpaired electrons

Chemistry - Module 4 (10 decks)

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