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Chemistry (Organic) > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

1
Q

What is a halogenoalkane

A

An alkane with 1 or more halogens attached to it

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2
Q

State the trend in boiling points of halogenoalkanes as we go down the halide group

A

Boiling point of halogenoalkanes increases down the group

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3
Q

Explain the trend in boiling points of halogenoalkanes as we go down the halide group

A

Boiling point increases due to:
- Atomic size increases
- More electrons
- Greater number of electrons
- Stronger VDW forces
- More energy needed to overcome these IMF

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4
Q

How do halogens affect the polarity of a bond

A

Halogens are electronegative and so pull the pair of electrons in a covalent bond towards it, making it polar

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5
Q

What is a nucleophile

A

An electron pair donor

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6
Q

Give 3 examples of nucleophiles

A

:CN-
:NH3
::OH-

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7
Q

Why can halogenoalkanes be attacked by nucleophiles

A

They contain polar bonds

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8
Q

When a halogenoalkane is attacked by a nucleophile in a substitution reaction, where is the first arrow from and where does it go to

A

From the lone pair on the nucleophile to the delta positive carbon bonded to the halogen

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9
Q

What is the name of the mechanism whereby hydroxide ions react with a halogenoalkane using an aqueous solvent

A

Nucleophilic substitution

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10
Q

What are the conditions required for the substitution reaction of hydroxide ions with a halogenoalkane

A

Warm aqueous NaOH
Carried out under reflux

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11
Q

Draw the substitution mechanism for the reaction of hydroxide ions with chloroethane using an aqueous solvent

A
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12
Q

What is formed when hydroxide ions react with a halogenoalkane using an aqueous solvent

A

An alcohol

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13
Q

What is the general equation for the overall reaction between a halogenoalkane and hydroxide ions using an aqueous solvent

A

RX + NaOH –> ROH + NaX
R - alkyl group (CH3)
X - Halogen

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14
Q

What is formed when halogenoalkanes react with cyanide ions

A

Nitriles

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15
Q

What are the conditions required for the reaction of cyanide ions with a halogenoalkane

A

Warm ethanolic potassium cyanide
Carried out under reflux

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16
Q

Draw the mechanism for the reaction of cyanide ions with chloroethane

A
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17
Q

What is the general equation for the overall reaction between cyanide ions and a halogenoalkane

A

RX + KCN –> RCN + KX
R - alkyl group (CH3)
X - Halogen

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18
Q

What is the name of the mechanism whereby cyanide ions react with a halogenoalkane

A

Nucleophilic substitution

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19
Q

What is the name of the mechanism whereby ammonia reacts with a halogenoalkane

A

Nucleophilic substitution

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20
Q

What are the conditions required for the reaction between ammonia and a halogenoalkane

A

Heat with ethanolic ammonia
Must have excess ammonia

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21
Q

What is produce when ammonia reacts with a halogenoalkane

A

An amine and an ammonium ion

22
Q

Why do we need excess ammonia in the reaction between ammonia and a halogenoalkane

A

As in the second phase of the reaction another molecule of NH3 acts as a base by reacting with hydrogen

23
Q

Draw the mechanism for the reaction of ammonia with a halogenoalkane

24
Q

How can an amine be identified

A

Fishy smell

25
Q

State the trend in reactivity of halogenoalkanes as we go down the halogen group

A

Halogenoalkanes become more reactive as we go down the group

26
Q

What determines the reactivity of a halogenoalkane

A

Bond strength/Bond enthalpy
Lower bond enthalpies mean weaker bond, easier to break and so more reactive

27
Q

What is the name of the mechanism where hydroxide ions react with a halogenoalkane using an ethanol solvent

A

Elimination

28
Q

What are the conditions required for the elimination reaction between hydroxide ions and a halogenoalkane

A

Hot ethanolic sodium hydroxide
Carried out under reflux

29
Q

What is the main difference in the mechanism between the reaction of hydroxide ions with a halogenoalkane using an aqueous solvent vs an ethanol solvent

A

The nucleophile attacks the hydrogen on the carbon adjacent to the carbon with the halogen attached with an ethanolic solvent (elimination), rather than the carbon directly attached to the halogen with an aqueous solvent(substitution)

30
Q

Outline and name the mechanism for when hydroxide ions react with 2 chloropropane using an ethanol solvent

A

Elimination

31
Q

What is formed when hydroxide ions react with a halogenoalkane, using ethanol as a solvent

A

An alkene
Water
Halide ion

32
Q

What is the role of OH- in the reaction of hydroxide ions with a halogenoalkane when using ethanol as a solvent

A

OH- acts as a base

33
Q

What is the role of OH- in the reaction of hydroxide ions with a halogenoalkane when using an aqueous solvent

A

OH- acts as a nucleophile

34
Q

What is an aqueous solvent essentially

35
Q

When reacting NaOH with a halogenoalkane, when do we form an alkene

A

When ethanol is used as the solvent

36
Q

When reacting NaOH with a halogenoalkane, when do we form an alcohol

A

When water is used as the solvent

37
Q

What is a CFC

A

Chlorofluorocarbons
Molecules which have had all their hydrogens replaced by chlorine and fluorine

38
Q

What is the issue with CFC’s

A

They break down ozone in the atmosphere

39
Q

How do CFCs break down ozone

A

C-Cl bonds are broken down by UV radiation in the atmosphere
Radicals are then formed which catalyse the breakdown of ozone

40
Q

Why are C-Cl bonds broken by UV in CFC’s and not C-F bonds

A

Easier to break as they have the lowest bond enthalpy (its a weaker bond)

41
Q

What is the formula for ozone

42
Q

What occurs in the initiation stage of the formation of chlorine radicals which catalyse the breakdown of ozone

A

Sunlight (UV) breaks down the C-Cl bond in a CFC producing 2 radicals which react with ozone molecules

43
Q

What 2 equations occur in the propagation stage of the formation of chlorine radicals which catalyse the breakdown of ozone

A

1- Cl radical reacts with O3 to form a ClO radical intermediate and O2
2 - ClO radical reacts with more O3 to make O2 and a Cl radical (reformed so is a catalyst)

44
Q

What occurs in the termination stage of the formation of chlorine radicals which catalyse the breakdown of ozone

A

Two Cl radicals react to form Cl2

45
Q

In which stage is ozone broken down. Initiation Propagation or termination. Write down the equation for this breakdown

46
Q

Write the 3 stages showing the breakdown of ozone from CCl3F

47
Q

Why are CFCs now banned

A

The risks of ozone depletion meaning less absorption of harmful UV radiation outweigh the benefits of using them in fridges and as a propellant in deodorants

48
Q

Why is ozone depletion a concern

A

Ozone absorbs most harmful UV radiation that causes skin cancer, depletion increases the risk of this

49
Q

What do we now use as an alternative to CFCs and why

A

HFC’s
Do not contain any chlorine

50
Q

Does a higher temperature encourage elimination or substitution for the reaction between OH- and halogenoalkanes

A

Higher temperatures encourage elimination

51
Q

Does a higher concentration of OH- encourage elimination or substitution for the reaction between OH- and halogenoalkanes

A

Higher concentrations favour elimination.

Chemistry (Organic) (14 decks)

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