Final answer:
Nucleophilic substitution occurs at the less hindered carbon atom in an asymmetrical epoxide.
Step-by-step explanation:
Nucleophilic substitution reactions occur when a group attached to an sp3 carbon is substituted for a more nucleophilic one. For asymmetrical epoxides, substitution typically occurs at the less hindered carbon atom.
This is because the less hindered carbon is more accessible to nucleophiles. The nucleophile attacks the less hindered carbon, resulting in a substitution reaction.