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Chemistry AS Module 2 > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

What is the functional group?

A

C-X

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2
Q

What is the general formula?

A

CnH2n+1X

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3
Q

What are primary, secondary and tertiary halogenoalkanes?

A

Primary - One carbon attached to the carbon bonded directly to the halogen
Secondary - Two “”
Tertiary - Three “”

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4
Q

What do strong electronegativity values in C-F and C-Cl give rise to? except when what?

A

Permanent dipole-dipole forces of attraction. Except when the molecule is symmetrical then it is non-polar.

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5
Q

What forces of attraction are between all halogenoalkanes?

A

Van der Waals

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6
Q

Why does 1-chlorobutane have a higher m.p than hexane

A

Hexane only has Van der Waals whereas 1-chlorobutane has both permanent dipole-dipole and Van der Waals

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7
Q

From chloromethane to Iodomethane what happens to the b.p?

A

Increases because the number of electrons increases, therefore Van der Waals increases.

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8
Q

What happens to the b.p when the carbon chain increases

A

Increases because the number of electrons increases therefore the number of induced dipoles increases and Van Der Waals increases

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9
Q

What happens when it becomes branched?

A

Becomes slightly less as they are unable to make as much contact with eachother.

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10
Q

What are some other properties of halogenoalkanes

A

1) They have a sweet, sickly smell

2) They are immiscible with water and form two distinct layers.

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11
Q

How are halogenoalkanes prepared

A

Prepared by reacting an alcohol with a hydrogen halide.

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12
Q

Show the preparation of 1-bromobutane from butan-1-ol

A

CH3CH2CH2CH2OH + HBr –> CH3CH2CH2CH2Br + H2O

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13
Q

How is the Hydrogen bromide generated?

A

In situ from the reaction of sodium bromide with concentrated sulfuric acid.
NaBr + H2SO4 → HBr + NaHSO4

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14
Q

What are the three types of reactions that produce halogenoalkanes?

A

1) From alkanes
Alkane + Halogen → Halogenoalkane + Hydrogen halide
Conditions - UV light
Mechanism - Free radical photochemical substitution

2) From alkenes
Alkene + Hydrogen halide → Halogenoalkane
Conditions - none
Mechanism - electrophilic addition

3) From alcohols
Alcohol + HX → Halogenoalkane + H2O
Conditions - HBr generated in situ from NaBr and H2SO4
Mechanism - Substitution

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15
Q

What happens when a halogenoalkane is reacted with an alkali, OH-?

A

It forms an alcohol + the halogen

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16
Q

What are the conditions necessary for a halogenoalkane to react with an alkali

A

Heat under reflux with aqueous Sodium Hydroxide and a small quantity of ethanol for 1 hour

17
Q

What is the mechanism?

A

Nucleophilic substitution / hydrolysis

18
Q

How do you acid hydrolyse a halogenoalkane? Whats the equation?

A

Heat the substance under reflux with dilute mineral acid.
With H+ written above the arrow
C2H5Br + H2O → C2H5OH + HBr

19
Q

How do you base catalyse a halogenoalkane? Whats the equation?

A

Heat the substance with dilute alkali

C2H5Br + NaOH → C2H5OH + NaBr

20
Q

What is the mechanism for the above two reactions?

A

Nucleophilic substitution

21
Q

What is the order of bond length and what does this mean?

A

C-I In order of decreasing bond length
C-Br
C-Cl

This means C-I bonds will hydrolyse more easily than C-Br and C-Br more easily than C-Cl.

22
Q

How do you demonstrate this experimentally?

A

Add 1㎤ of each halogenoalkane to a test tube, add 2㎤ of ethanol and 1㎤ of silver nitrate solution to each. Place them into hot water. First a yellow ppt, then a cream ppt, the lastly a white ppt. Yellow = I, Cream = Br and White = Cl

23
Q

What is the equation for the reaction of a halogenoalkane with ammonia

A

Forms an amine and a hydrogen halide

C2H5Br + NH3 → C2H5NH2 + HBr

24
Q

What conditions are required ?

A

Heated with ethanolic ammonia in a sealed tube

25
Q

What is the mechanism?

A

Nucleophilic substitution

26
Q

What is the reaction of a halogenoalalkane and Cyanide ions

A

Forms a nitrile and the halide ion

C2H5Br + CN- →C2H5CN + Br-

27
Q

What are the conditions necessary for cyanide ions to react with a halogenoalkane

A

Halogenoalkane dissolved in ethanol dropped into an aqueous solution Potassium Cyanide KCN

28
Q

What is the mechanism?

A

Nucleophilic substitution

29
Q

What is the reaction of sodium/potassium hydroxide in ethanol?

A

Halogenoalkane + KOH → Alkene + KX + H2O
Conditions - Halogenoalkane treated with hot ethanolic potassium hydroxide solution
Elimination reaction as a H and Br is eliminated

30
Q

Draw the hydrolysis of a primary halogenoalkane

A

in book

31
Q

Draw the hydrolysis of a tertiary halogenoalkane

A

in book

32
Q

What effect do CFCs have on ozone?

A

Ozone absorbs UV light. The chlorine free radical reacts with O3 forming a ClO• radical and oxygen gas.
The ClO• radical reacts with more O2 forming 2O2 and Cl• and the cycle continues. This means that there is less and less O3 in the atmosphere so more UV light gets through.

Chemistry AS Module 2 (11 decks)

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