Halogenoalkanes

Question 1

What is the definition of a primary halogenoalkane

Answer 1

A halogenoalkane which has one carbon atom directly bonded to the carbon atom that is bonded to the halogen

Question 2

What is the definition of a secondary halogenoalkane

Answer 2

A halogenoalkane which has two carbon atoms directly bonded to the carbon atom that is bonded to the halogen

Question 3

What is the definition of a tertiary halogenoalkane

Answer 3

A halogenoalkane which has three carbon atoms directly bonded to the carbon atom that is bonded to the halogen

Question 4

What is the definition of reflux

Answer 4

Repeated boiling and condensing of a reaction mixture

Question 5

What is the definition of miscibility

Answer 5

Liquids which mix in all proportions

i.e form a single layer

Question 6

What is the definition of a nucleophile

Answer 6

An ion or molecule with a lone pair of electrons that attacks regions of low electron density

Question 7

What is definition of substitution

Answer 7

Replacing one atom or group with a different atom of group

Question 8

What is the definition of hydrolysis

Answer 8

Breaking up molecules by reaction with water

Question 9

What is the definition of elimination

Answer 9

A reaction in which a small molecule is removed from a larger molecule

Question 10

What is the general formula for a halogenoalkane

Answer 10

CnH2n+1 X

X = halogen atom

Question 11

What are the physical properties of halogenoalkanes

Answer 11

⭕️ polar - electronegative halogen - permanent dipole dipole attractions 
⭕️ don’t dissolve in water 
⭕️ denser than water - forms two layers
⭕️ presence of halogen raises bp 
⭕️ soluble in organic

Question 12

How do the boiling points of halogenoalkanes compare to molecules of similar RFM

Answer 12

Higher bp

Due to presence of electronegative halogen - need more energy to break dipole dipole attractions

Question 13

Describe the trend in bp as the halogen atom is changed

Answer 13

Increase in RFM
Increase in number of electrons
Stronger VDW forces
More energy to break

Question 14

What happens to the bp of halogenoalkanes if the carbon chain increases

Answer 14

Bp increases
More electrons
Stronger VDW forces
More energy

Question 15

Which has a higher bp, a primary or secondary halogenoalkane. Why

Answer 15

Primary
Halogen at end of molecule
Chain packs tightly together
Stronger VDW

In secondary:
Reduces contact between hydrocarbon chain
Weaker VDW

Question 16

How do you prepare bromoalkane from primary alcohol

Answer 16

Substitution with HBr

Reflux mixture of H2SO4, NaBr, butan-1-ol

Question 17

Why are chlorofluorocarbons bad for the ozone layer

Answer 17

⭕️ ozone allotrope of oxygen - absorbs UV
⭕️ layer over Antarctica reduced - more UV reaching earth - melt caps
⭕️ C-F and C-Cl don’t break down in lower atmosphere
⭕️ in upper atmosphere homolytic fission occurs - chlorine radicals - photochemical chain reactions
⭕️ chlorine radicals break down ozone layer

Question 18

How do you eliminate a halogen
Write the equation
What is produced

Answer 18

Ethanolic KOH
See notes
Alkene, KBr and H2O

Question 19

How many steps are in an SN2 mechanism

Answer 19

Single step

Question 20

What type of mechanism is the hydrolysis of a primary bromoalkane

Answer 20

SN2

Question 21

What type of mechanism and how many steps are in the hydrolysis of a tertiary bromoalkane

Answer 21

SN1

2 step

Question 22

Draw the mechanism for an SN1 mechanism

Answer 22

See notes

Question 23

How does the rate of hydrolysis change as you go down the group

Answer 23

Easier to hydrolyse as you go down the group because bond enthalpy decreases down the group

Question 24

Draw the mechanism for an SN2 mechanism

Answer 24

See notes