Halogenoalkanes Flashcards
What is the definition of a primary halogenoalkane
A halogenoalkane which has one carbon atom directly bonded to the carbon atom that is bonded to the halogen
What is the definition of a secondary halogenoalkane
A halogenoalkane which has two carbon atoms directly bonded to the carbon atom that is bonded to the halogen
What is the definition of a tertiary halogenoalkane
A halogenoalkane which has three carbon atoms directly bonded to the carbon atom that is bonded to the halogen
What is the definition of reflux
Repeated boiling and condensing of a reaction mixture
What is the definition of miscibility
Liquids which mix in all proportions
i.e form a single layer
What is the definition of a nucleophile
An ion or molecule with a lone pair of electrons that attacks regions of low electron density
What is definition of substitution
Replacing one atom or group with a different atom of group
What is the definition of hydrolysis
Breaking up molecules by reaction with water
What is the definition of elimination
A reaction in which a small molecule is removed from a larger molecule
What is the general formula for a halogenoalkane
CnH2n+1 X
X = halogen atom
What are the physical properties of halogenoalkanes
⭕️ 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
How do the boiling points of halogenoalkanes compare to molecules of similar RFM
Higher bp
Due to presence of electronegative halogen - need more energy to break dipole dipole attractions
Describe the trend in bp as the halogen atom is changed
Increase in RFM
Increase in number of electrons
Stronger VDW forces
More energy to break
What happens to the bp of halogenoalkanes if the carbon chain increases
Bp increases
More electrons
Stronger VDW forces
More energy
Which has a higher bp, a primary or secondary halogenoalkane. Why
Primary
Halogen at end of molecule
Chain packs tightly together
Stronger VDW
In secondary:
Reduces contact between hydrocarbon chain
Weaker VDW
How do you prepare bromoalkane from primary alcohol
Substitution with HBr
Reflux mixture of H2SO4, NaBr, butan-1-ol
Why are chlorofluorocarbons bad for the ozone layer
⭕️ 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
How do you eliminate a halogen
Write the equation
What is produced
Ethanolic KOH
See notes
Alkene, KBr and H2O
How many steps are in an SN2 mechanism
Single step
What type of mechanism is the hydrolysis of a primary bromoalkane
SN2
What type of mechanism and how many steps are in the hydrolysis of a tertiary bromoalkane
SN1
2 step
Draw the mechanism for an SN1 mechanism
See notes
How does the rate of hydrolysis change as you go down the group
Easier to hydrolyse as you go down the group because bond enthalpy decreases down the group
Draw the mechanism for an SN2 mechanism
See notes
