These reactions are favoured when they occur at a sterically hindered carbon centre. For 10 points each:
[10m] Name this reaction mechanism, in which a leaving group is replaced [emphasise] after the formation of a carbocation intermediate, giving a rate law that is considered independent of the concentration of the incoming species.
ANSWER: SN1 [or unimolecular nucleophilic substitution; accept nucleophilic substitution 1; prompt on partial answer, do not accept or prompt on SN2 or bimolecular etc.]
[10h] Because they stabilise both the charged intermediate and the leaving group, speeding up the reaction, solvents for SN1 reactions are commonly chosen to have these [emphasise] two properties.
ANSWER: polar and protic [do not accept or prompt partial answers]
[10e] Common reactants in SN1 reactions include secondary and tertiary haloalkanes, in which an alkane has a hydrogen substituted by an element from group 7. Because its anion is a good leaving group, this element, below chlorine and above iodine in the periodic table, is a common choice.
ANSWER: bromine [or Br; accept bromide or Br- (“B R minus”)]