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AS CHEMISTRY > HALOGENOALKANES > Flashcards

HALOGENOALKANES Flashcards

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1
Q

Define primary halogenoalkane

A

One carbon attached to the at in atom adjoining the halogen

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2
Q

Define secondary halogenoalkane

A

Two carbons attached to the carbon atom anointing the halogen

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3
Q

Define tertiary halogenoalkane

A

Three carbons attached tot the carbon stoma joining the halogen

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4
Q

What are the two reactions halogenoalkanes can undergo

A

Substitution

Elimination

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5
Q

Define substitution

A

Swapping a halogen atom for another atom or groups of atoms

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6
Q

Define nucleophile

A

Electron pair donor

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7
Q

Give an example of a nucleophile

A

:OH-

:NH3

CN-

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8
Q

Outline nucleophilic substitution

A

The nucleophile attack the (delta) positive carbon atom

The carbon has a small positive charge because of the electronegativity difference between carbon and the halogen

The nucleophile replaces the halogen on the alkane

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9
Q

How is the rate of a substitution reaction affected by the strength of the carbon-halogen bond?

A

The weaker the bond
The easier it is to break
And the faster the reaction

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10
Q

What is the trend in rate of a substitution reaction of halogenoalkanes?

A

Iodo alkanes substitute the fastest

Fluoroalkanes substitute the slowest

Because C-I bonds have the weakest bond enthalpy

And C-F bonds have the strongest bond enthalpy

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11
Q

Define hydrolysis

A

Splitting a molecule by reaction with water

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12
Q

Describe water as a nucleophile

A

Water is a POOR nucleophile

But reacts slowly with haloalkanes in a substitution reaction

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13
Q

Describe the reaction between aqueous silver nitrate and haloalkanes

A

Halide group combined with silver ion to form a silver halide precipitate

I- + Ag+ -> AgI

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14
Q

Describe the colour of silver ha life precipitates

Which form fastest?

A

AgI (yellow) forms fastest
AgBr (cream)
AgCl (white) forms slowest

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15
Q

Describe the conditions of nucleophilic substitution with aqueous hydroxide ions

A

Potassium (or sodium) hydroxide reagent

Aqueous solution

Heat under reflux

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16
Q

Describe the change in halogenoalkane when substituted in aqueous hydroxide ions

A

Forms an alcohol

17
Q

Why is the aqueous condition important in nucleophilic substitution with hydroxide ions

A

Ethanol would trigger an elimination reaction

18
Q

Outline tertiary halogenoalkane nucleophilic substitution

A

The halogen breaks away from haloalkane

To form a carbocations intermediate

The hydroxide nucleophile then attacks the positive carbon

19
Q

Describe the conditions of nucleophilic substitution with cyanide ions

A

KCN dissolved in ethanol/water mixture reagent

Heating under reflux

20
Q

Outline the change in rules for naming nitriles

A

Nitriles have to be at the end of a chain

Start numbering the chain from the c in CN

Include the e (butanenitrile not butannitrile)

21
Q

Describe the conditions of nucleophilic substitution with ammonia

A

NH3 dissolved in ethanol reagent

Heating under pressure

22
Q

Outline nucleophilic substitution with ammonia

A

The ammonia attack the (delta) positive carbon atom

The ammonia replaces the halogen on the alkane producing a halogen radical

Excess ammonia then reacts with the hydrogen on the positive charged nitrogen

23
Q

Why must excess ammonia be used in nucleophilic substitution

A

To minimise a lower yield due to further substitution reactions occurring

24
Q

Define elimination

A

Removal of small molecule (often water) from the organic molecule

25
Q

Outline the conditions for elimination with alcoholic hydroxide ions

A

Potassium (or sodium) hydroxide reagent

In ethanol

With heat

26
Q

Outline elimination with alcoholic hydroxide ions

A

The radical reacts with a hydrogen bonded to a neighbouring carbon to the halogen

The bond between mentioned hydrogen and carbon breaks to form a double bond between carbon carbon atoms

The halogen group forms a negative ion

And H2O

27
Q

What types of reaction are likely to occur between primary and tertiary halogenoalkanes

A

Primary tends toward substitution

Tertiary tends toward elimination

28
Q

What are some of the uses of halogenoalkanes

A

Chloroalkane a and chlorofluoroalkanes can be used as solvents in dry cleaning

Refrigerants

Pesticides

Aerosol propellants

29
Q

Why have many uses of halogenoalkanes been stopped?

A

Toxic

Detrimental effects on the atmosphere

30
Q

Why is the ozone layer benefitial

A

Filters out harmful UV radiation

31
Q

What does ozone in the lower atmosphere do

A

Pollutes

Contributes toward smog formation

32
Q

Outline the conditions for nucleophilic substitution of halogenoalkanes with aqueous hydroxide ions

A

Potassium/Sodium hydroxide

Aqueous solution heat under reflux

Neucleophile OH-

AS CHEMISTRY (17 decks)

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