Complex sentence: In organic chemistry, "ortho" (along with "meta" and "para") is used to distinguish the three types of isomer of disubstituted benzenes: it indicates that the substituents are at locants 1 and 2.
Split into simpler sentences: In organic chemistry, the prefixes "ortho -", "meta -" and "para-" are used to distinguish the three types of isomer of disubstituted benzenes. The prefix "ortho -" indicates that the substituents are at locants 1 and 2.