a. SN2 leads to a racemization of sterechemistry due to the nucleophile attacking from the backside and the leaving group leaving.
b. A primary alkyl halide will tend to react through an SN2 mechanism because there is little hindrance to backside attack and a primary carbocation is not very stable.
c. 1-bromopentane will undergo substitution through an SN2 mechanism.
d. If R-3-bromo-3-methylhexane is allowed to react with OH-, the product will be a 50%/50% mixture of R-3-methyl-3-hexanol and S-3-methyl-3-hexanol.
e. SN1 leads to a racemization of sterechemistry due to the nucleophile attacking from the backside and the leaving group leaving.