The isomers of cinnamic acid mainly include the following:

1. Cinnamic acid: the molecular formula is C9H8O2 and the molecular weight is 148.16. Compared with cinnamic acid, its The positions of the benzene ring and the vinyl group are interchanged, which is a stereoisomer of cinnamic acid.

2. Meta-cinnamic acid: The molecular formula is C9H8O2 and the molecular weight is 148.16. Compared with cinnamic acid, the hydrogen in the middle position of its benzene ring is replaced by a hydroxyl group, and it is an isomer of cinnamic acid.

3. Isocinnamic acid: The molecular formula is C10H10O2 and the molecular weight is 162.19. Compared with cinnamic acid, it has two methyl groups on its benzene ring and is an isomer of cinnamic acid.