Haloalkanes and Alkenes

Question 1

Primary halogenoalkanes

Answer 1

One carbon attached to the carbon atom adjoining the halogen.

Question 2

Secondary halogenoalkanes

Answer 2

Two carbon atoms attached to the carbon atom adjoining the halogen

Question 3

Tertiary halogenoalkanes

Answer 3

Three carbons attached to the carbon atom adjoining the halogen

Question 4

What to remember when drawing the nucleophilic substitution mechanism?

Answer 4

Double headed arrows

Goes behind the carbon which the halogen is attached to

Make sure to draw in the dipoles

Make sure the curly arrow comes from the lone pair which is drawn in

remember about the halogen that is displaced

Question 5

What nucleophiles do Halogenoalkanes undergo nucleophilic substitution?

Answer 5

OH-, CN- and NH₃.

Question 6

What is the most unreactive and most reactive haloalkane and why?

Answer 6

Unreactive = Fluoroalkanes

Reactive = Iodoalkane

Iodoalkanes have more electrons and so have a larger atomic radius and so there is less attraction between the halogen and the carbon. They have a lower bond enthalpy.

Question 7

Hydrolysis

Answer 7

The splitting of a molecule by reaction with water.

Question 8

What colour is Silver Chloride?

Answer 8

White precipitate

Question 9

What colour is Silver Bromide?

Answer 9

Cream Precipitate

Question 10

What colour is Silver Iodide?

Answer 10

Yellow Precipitate

Question 11

How can the rate of reaction be determined from the precipitate?

Answer 11

The faster the precipitate is formed, the faster the rate of reaction.

Question 12

Conditions needed to substitute a halogen with an OH- ion?

Answer 12

Potassium hydroxide in an aqueous solution under heat.

Question 13

Conditions needed for nucleophilic substitution of a CN- ion?

Answer 13

Ethanolic (dissolved in ethanol) Potassium Cyanide

Under heat

Question 14

Conditions needed for Nucleophilic substitution of a haloalkane by NH3?

Answer 14

Excess Ethanolic Ammonia

Under heat and pressure

Question 15

What happens in an elimination reaction?

Answer 15

A nucleophile attacks a hydrogen atom and such as a hydroxide nucleophile and forms an alkene and water and the halide ion.

Question 16

What is ozone?

Answer 16

Ozone is an allotrope of oxygen which is found in the upper atmosphere and is beneficial as it filters out lots of the sun’s harmful UV radiation.

Question 17

What are the three types of radiation from the sun?

Answer 17

UV-A (none absorbed by the ozone)
UV-B (most absorbed by the ozone)
UV-C (all absorbed by the ozone)

Question 18

What is the condition needed for the decomposition of ozone?

Answer 18

Chlorine radicals which come from uv light breaking down the C-Cl bond

Question 19

What are some examples of where CFCs were used and why were they banned?

Answer 19

They were used in fridges, degreasing circuit boards, as propellants in aerosols

They were banned as they were found to be damaging the ozone layer.

Question 20

What are the three steps of free radical substitution and what are the conditions needed for each?

Answer 20

Initiation (UV light)
Propagation
Termination

Question 21

Under UV light what does trichlorofluoromethane break down to?

Answer 21

Chlorine radicals and a dichlorofluoromethane radical

Question 22

What to remember when drawing an elimination mechanism?

Answer 22

Remember to draw the base attacking an adjacent hydrogen and to show all the electron pairs moving.

Show water and halogen ion.

Question 23

Conditions needed for electrophilic addition for Br2, Cl2 and HBr?

Answer 23

No conditions needed.

Question 24

Conditions needed for catalytic addition with H2.

Answer 24

Nickel catalyst at 150°C

Question 25

Conditions needed for electrophilic addition with H2O?

Answer 25

300°C 60ATM and H₃PO₄

Question 26

Explain why Bromine, a non polar molecule, is able to react with propene?

Answer 26

The double bond is electron rich and forms and induced dipole with Bromine.

Question 27

What features of the double bond in an alkene stop it from switching between isomers?

Answer 27

Restriction in rotation.

Question 28

What to remember when drawing the electrophilic addition mechanism?

Answer 28

remember that there are three steps

make sure to draw the arrow coming from the double bond and going to the less electronegative atom

make sure to draw the carbon cation

show dipoles and temporary charges

Question 29

What is the major product of any electrophilic addition?

Answer 29

The tertiary then secondary then primary

Question 30

Why does electrophilic addition happen?

Answer 30

As the electrophile approaches the molecule the electron rich double bond pushes the electrons away in the electrophile molecule and it splits up.

Question 31

What is a nucleophile?

Answer 31

A nucleophile is a reactant that provides a pair of electrons to form a new covalent bond.

Question 32

What is an electrophile?

Answer 32

An electrophile is a species that accepts a pair of electrons to form a new covalent bond

Question 33

What specifically happens when a haloalkane reacts with an ammonia nucleophile?

Answer 33

To start with the ammonia acts like any other nucleophile but forms an ammonia part which has a positive charge and so another ammonia molecule which now acts as a base comes along and and grabs and electron from a hydrogen to make an ammonium molecule as well.

https://www.youtube.com/watch?v=akbSB6fRlj4

Question 34

Where are chlorofluoroalkanes used?

Answer 34

They are used in solvents.

Question 35

How do chlorine radicals deplete the ozone layer and what are the propagation steps?

Answer 35

Cl⠈+ O₃ = O₂ + OCl⠈

OCl⠈ + O₃ = 2O₂ + Cl⠈

Question 36

How can you differentiate between an E and a Z isomer?

Answer 36

E isomers have a greater atomic mass diagonally from each other

Z isomers have a greater atomic mass adjacent horizontal to each other

Question 37

What happens in the electrophilic addition of H2SO4 with an alkene?

Answer 37

A hydrogen splits away from the H2SO4 and OSO2OH is left which attaches to the final open bond.

Then in step 2 water is added and the compound is hydrolysed into an alcohol and also sulfuric acid in the end.

Question 38

What is the role of sulfuric acid in its electrophilic addition?

Answer 38

It acts as a catalyst

Question 39

What is the structure of an alkene in terms of sigma and pi bonds?

Answer 39

The double bond contains one pi bond and one sigma bond, the pi bond is exposed and is electron rich which is what the electrophiles are attracted to.

Question 40

Problems with polymers being unreactive?

Answer 40

They don’t decompose and if they are burnt then they release carbon dioxide which contributes to the greenhouse effect.

Question 41

What are the conditions needed for elimination?

Answer 41

A strong base

hot ethanolic conditions

Question 42

What to remember when drawing a repeating unit?

Answer 42

dont put down an n
You will get marked down

C-C single bond (not double)

Bonds passing through brackets

Question 43

What solubility is silver fluoride?

Answer 43

Soluble in water so silver nitrate cannot be used to test for fluoride ion as there will be no colour change.

Question 44

What to remember when talking about the quantity of products of a mechanism?

Answer 44

When talking about the quantity of product produced remember to mention both types of product and in what quantity and the differences in the cation intermediate.