6.4 Halogenoalkanes Flashcards
Classifying, nucleophillic substitution + mechanism, hydrolysis, reactivity
What are haloalkanes?
Saturated organic compounds that contain carbon atoms and at least one halogen atoms
Are halogenoalkanes soluble in water?
Insoluble as C-H bonds are non-polar, not compensated for enough by C-X bond polarity
Do halogenoalkanes have a polar bond? Why?
Yes polar, as halogen has a higher electronegativity than C (halogen is δ-, carbon is δ+)
What type intermolecular forces do halogenoalkane have? Why?
Permanent dipole-dipole and London forces of attraction
C-X bond polarity creates permanent dipoles
When would halogenoalkanes have higher boiling points?
Increase Carbon chain length
Halogen further down group 7
How would the mass of a haloalkane compare with the mass of an alkane of the same chain length?
Greater as mass of halogen > mass of H
What is the most important factor in determining halogen reactivity?
The strength of carbon halogen bond
What would bond polarity suggest the order of reactivity would be?
C-F would be most reactive as most polar bond
What would bond enthalpies suggest the order of reactivity would
be?
C-I would be most reactive as lowest bond enthalpy
What is the trend in reactivity of primary, secondary and tertiary haloalkanes?
● The tertiary halide produces a precipitate almost instantly.
● The secondary halide gives a slight precipitate after a few seconds.
● The primary halide takes considerably longer to produce a
precipitate.
Define nucleophile
Electron pair donor
Give 3 examples of nucleophiles
:OH -
:CN -
:NH 3 -
What is nucleophilic substitution?
A reaction where a nucleophile donates a lone pair of electrons to δ+ C atom, δ− atom leaves molecule (replaced by nucleophiles)
What is hydrolysis?
A reaction where water is a reactant
What reactant often produces hydroxide ions for hydrolysis?
Water
What fission does water undergo to produce OH- ?
Heterolytic fission
What are the conditions/reactants needed for the elimination reaction of haloalkanes?
NaOH or KOH dissolved in ethanol (no water present)
Heated
What is formed in the elimination reaction of haloalkanes?
An alkene, water and halogen ion
How can you convert a haloalkane into an amine?
Reagent: NH 3 dissolved in ethanol
Conditions: Heating under pressure in a sealed tube
Mechanism: Nucleophilic Substitution
Type of reagent: Nucleophile - ammonia
How do you convert halogenoalkane into alkene?
Use ethanolic potassium hydroxide to produce alkenes (where the hydroxide ion acts as a base)
How do you produce nitriles from haloalkane?
Use potassium cyanide to produce nitriles (where the cyanide ion acts as a nucleophile)
How can you compare the rate of hydrolysis of haloalkanes?
Aqueous silver nitrate is added to a halogenoalkane and a silver halide precipitation is formed. The quicker the precipitate is formed the faster the rate of
hydrolysis.
AgI (s) - yellow precipitate [fastest]
AgBr(s) – cream precipitate
AgCl(s) – white precipitate
