Complex sentence: For imides derived from amines (vs. ammonia), the "N"-substituent is indicated by a prefix, e.g., N-ethylsuccinimide is derived from succinic acid and ethylamine.
Split into simpler sentences: For imides derived from amines (as opposed to ammonia), the "N"-substituent is indicated by a prefix. For example, N-ethylsuccinimide is derived from succinic acid and ethylamine.