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chemistry paper 2 > halogenoalkanes > Flashcards

halogenoalkanes Flashcards

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1
Q

What do halogenoalkanes contain

A

Polar bonds

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2
Q

How do you name halogenoalkanes

A

The halo part of the name comes first, along with a number to indicate where the halogen is -(if needed). If there is more than one type of halogen put the prefixes in alphabetical order.

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3
Q

How can haloalkanes be classified

A

o Primary
o Secondary
o Tertiary

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4
Q

Why is something a haloalkane

A

The Haloalkanes are alkanes that contain a halogen, F, Cl, Br, I

One or more H atoms have been replaced by a halogen

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5
Q

What is a primary haloalkane

A

• In a primary haloalkane the halogen is attached to a C, which is only attached to one other C.

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6
Q

What is a secondary haloalkane

A

• In a secondary haloalkane the halogen is attached to a C, which is only attached to two other C’s.

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7
Q

What is a tertiary haloalkane

A

• In a tertiary haloalkane the halogen is attached to a C, which is attached to three other C’s.

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8
Q

An alkane with a halogen needs what to form into a haloalkane

A

Uv light

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9
Q

What is the reaction called that goes from an alkane to a halo alkane

A

Substitution reaction

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10
Q

Define a free radical

A

A free radical is a species which has a single unpaired electron.

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11
Q

Cl2 -> 2Cl .

Why is UV light needed to start the reaction?

A

UV light provides the energy needed to break THE Cl-Cl bond.

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12
Q

What is homolytic fission

Cl2 -> 2Cl .

A

Both Cl atoms have donated one pair of electrons into the covalent bond, and when the bond breaks they each take back their electron.

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13
Q

Define a Nucleophile

A

Can donate a lone pair of electrons, a lone pair donor
E.g OH–, CN– and NH3

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14
Q

What is a Nucleophilic substitution

A

The replacement of a halogen by a nucleophile

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15
Q

What are the 3 reactions of the haloalkanes

A

Nucleophilic substitution by hydroxide ions (OH-, hydrolysis)
Nucleophilic substitution by cyanide ions (CN-)
Nucleophilic substitution with ammonia (NH3)

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16
Q

Haloalkane -> Nitrile

What is the reaction
What is the reagent
What is the condition

A

Nucleophilic substitution by cyanide ions (CN-)

KCN
Water & ethanol

17
Q

Haloalkane -> Amine

What is the reaction
What is the reagent
What is the condition

A

Nucleophilic substitution with ammonia (NH3)

NH3
Excess

18
Q

Haloalkane -> Alcohol

What is the reaction
What is the reagent
What is the condition

A

Nucleophilic substitution by hydroxide ions (OH-, hydrolysis)

NaOH
Aqueous solvent, heat under reflux

19
Q

What is the nucleophilic substitution of a haloalkane using hydroxide ions called

A

Hydrolysis

20
Q

Explain why the carbon–halogen bond enthalpy influences the rate of reaction

Bond Strength (kJ mol-1)
C-F -> + 467
C-Cl -> +340
C-Br -> +280
C-I -> +240

A

As the bond enthalpy (strength or heat energy needed to break a bond) decreases it is easier to break the
C – Halogen bond.

The stronger the bond the harder it is to break and the slower the rate of reaction will be as more energy is required to break it.

The weaker the bond the faster the rate will be.

21
Q

Explain why the c-I bond is the weakest and the C-Cl bond is the strongest

Bond Strength (kJ mol-1)
C-F -> + 467
C-Cl -> +340
C-Br -> +280
C-I -> +240

A

C – I​- weakest bond so fastest reaction, less energy require to break the bond

C – Cl ​- strongest bond so slowest reaction, more energy required to break the bond

22
Q

Where is ozone formed naturally

A

Ozone is formed naturally in the upper atmosphere (stratosphere) by free radical reactions

23
Q

What are replacements for CFC’s which are chlorine free

A

Alkanes, HFC’s hydrofluorocarbons and HCFC’s hydrochlorofluorocarbons are used frequently.

Carbon dioxide is used as a replacement for blowing agents for expanded polymers (as in polystyrene).

24
Q

Where are chlorine atoms formed and how

A

formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break

25
Q

How do CFC’s damage the ozone layer

A

Spec - Cl. Acts as a catalyst in the decomposition of ozone. One Cl. Radical breaks down many ozone molecules.

26
Q

What are the useful properties of CFC

A

• non-toxic
• inert gases
• volatile

27
Q

What are the replacements for CFC’s

A

Trichlorofluoromethane -> Refrigeration Air conditioning
Dichlorodifluromethane -> aerosol propellants, blowing agent for polystyrene
1,1,1 trichloro 2,2,2 trifluoroethane -> dry cleaning agents, degreasing agents for circuit boards

28
Q

How does chlorine atoms catalyse decomposition of ozone
What are the two equations you need to know

A

Spec based - Cl• + O3 → ClO• + O2 and ClO• + O3 → 2O2 + Cl•

29
Q

What is the role of the hydroxide ion in an elimination reaction

A

A base, as it is removing a hydrogen from the molecule

30
Q

Haloalkane -> Alkene

What is the reaction
What is the reagent
What is the condition

A

Elimination

KOH or NaOH
Ethanolic, reflux

chemistry paper 2 (14 decks)

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