Revision MaterialsCardiff High School
2.6 Halogenoalkanes
a) / Define what is meant by the following:i)Elimination
ii)Nucleophile
iii)Nucleophilic eliminiation
State the reagents used and any conditions necessary to convert a halogenoalkanes to alkenes.
Give the mechanism for the formation of the following:
i)Propene from 1-bromopropene
ii)But-2-ene and but-1-ene from 2-bromobutane
b) / Define what is meant by the following:
i)Substitution
ii)Nucleophilic substitution
State the reagents used and any conditions necessary for a nucleophilic substitution reaction.
Outline the mechanism for the following reactions, including any relevant dipoles, lone pairs and charges:
i)Chloromethane with aqueous sodium hydroxide
ii)Iodoethane with potassium cyanide
iii)Bromoethane with ammonia
iv)Chloroethane with sulphuric acid
State which of the above reactions could also be considered a hydrolysis reaction.
c) / Using ideas about bond enthalpies predict the relative rates of reactions i, ii, iii, iv in the question above.
Using ideas about bond polarity make separate predictions about the relative rates of these reactions.
Explain why the actual reactivities follow the trends predicted according to bond enthalpies and not bond polarity. (Hint: Consider the relative influence of both factors)
d) / Samples of iodoethane, 2,2-dichlorobutane and 1,2,3-trichloromethane are found unlabelled in a laboratory. Give an initial test including any expected observations and reagents that could be done to identify these chemicals.
Give a further test that could be conducted to unequivocally deduce the identity of each of these samples.
e) / Evaluate the usefulness of halogenoalkanes. Your answer should consider the following:
- Their uses
- Environmental issues
- Reasons for regulation
f) / Define what is meant by CFCs
Explain why the use of CFCs is now severely limited. Include in your answer any relevant equations.
Describe why HFCs are used as replacement for CFCs. Your answer should consider the relative bond enthalpies of the carbon to halogen bonds found in each molecule.
g) / Label the apparatus and annotate the diagram below to describe how reflux can be used to heat a reaction in a controlled environment.