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Chemistry > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

1
Q

What is a nucleophile?

A

An electron-rich species that can donate a pair of electrons

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2
Q

What is the meaning of a nucleophile?

A

Means ‘nucleus/positive charge loving’ as they are attracted to positively charged species

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3
Q

What is the nucleophile in the formation of alcohols?

A

The hydroxide ion OH-

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4
Q

What is used to form an alcohol?

A

An aqueous solution of sodium hydroxide or potassium hydroxide with ethanol

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5
Q

Why is the reaction mixture to form an alcohol warmed?

A

It is very slow at room temperature

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6
Q

What kind of reaction is the formation of an alcohol?

A

Hydrolysis

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7
Q

What does the rate of reaction of the formation of an alcohol depend on?

A

The type of halogen in the halogenoalkane - the stronger the CX bond, the slower the rate of reaction

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8
Q

Which halogenoalkanes don’t react in the formation of an alcohol and which do?

A

Fluoroalkanes don’t react but iodoalkanes react very quickly

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9
Q

Apart from the hydroxide ion, what can the formation of an alcohol from a halogenoalkane also use as the nucleophile?

A

Water - but it is very slow

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10
Q

Why is the hydroxide ion a better nucleophile than water in the formation of an alcohol?

A

OH- carries a full negative charge and the O in H2O only carries a partial negative charge

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11
Q

What will happen when halogenoalkanes react with water?

A

H2O is a weak nucleophile but will eventually substitute for the halogen and an alcohol will be formed

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12
Q

What happens if we add silver nitrate solution in ethanol to the reaction of halogenoalkanes with water?

A

The silver ions will react with the halide ions as soon as they form, giving a silver halide precipitate

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13
Q

What is the nucleophile in the formation of nitriles?

A

Cyanide ion CN-

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14
Q

What do we need to do in order to form a nitrile from a halogenoalkane?

A

An ethanolic solution of potassium cyanide (KCN in ethanol) is heated under reflux with the halogenoalkane

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15
Q

Give an example of the formation of a nitrile?

A

bromoethane + ethanol potassem cyanide = propanenitrile
CH3CH2Br + CN- = CH3CH2CN + Br-

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16
Q

What happens to the carbon chain in the formation of a nitrile?

A

It is extended by adding an extra carbon

17
Q

How can the formation of nitriles be used by chemists?

A

To make a compound with 1 more carbon atom than the best available organic starting material

18
Q

What is the nucleophile in the formation of primary amines?

A

Ammonia - NH3

19
Q

What do we need to do in order to form a primary amine from a halogenoalkane?

A

An ethanolic solution of excess ammonia is heated under pressure with a primary halogenoalkane

20
Q

Why is an excess of ammonia used in the formation of a primary amine?

A

The product is more reactive than ammonia so further substitutions could occur

21
Q

Give an example of the formation of a primary amine?

A

CH3CH2Br + NH3 = CH3CH2NH2 + HBr

22
Q

What do we need to do the formation of an alkene from a halogenoalkane?

A

The halogenoalkane is heated under reflux with ethanolic NaOH

23
Q

What happens as a result of heating the halogenoalkane under reflux to form an alkene?

A

The C-X bond breaks heterolytically, forming an X- ion and leaving an alkene as an organic product

24
Q

Give the equation for the formation of an alkene from a halogenoalkane?

A

Halogenoalkane + NaOH(ethanol) = alkene + water + NaX

25
Q

What kind of reaction is a nucleophilic substitution?

A

One in which a nucleophile attacks a carbon atom which carries a partial positive charge

26
Q

What is replaced by the nucleophile in nucleophilic substitution?

A

An atom that has a partial negative charge

27
Q

Why will halogenoalkanes undergo nucleophilic substitution?

A

Due to the polar C-X bond
X has higher electronegativity than C

28
Q

What is the mechanism when halogenoalkanes react with aqueous potassium hydroxide?

A

The OH- (nucleophile) displaces the Br- atom and donates 2 electrons to the carbon atom, forming an alcohol and bromine ion

29
Q

What is the mechanism when halogenoalkanes react with ammonia?

A
  • Lone pair on ammonia attacks partially positive carbon atom
  • C-X bond breaks
    -Second molecule of NH3 acts as a base and removes a proton
  • N-H bond breaks and lone pair is restored

Chemistry (10 decks)

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