Ferulic acid dimers structure

In the case of ferulic acid, dimers are known one of these has a difuran structure and another a benzofuran structure. 

Dimeric forms of ferulic and p-coumaric acids also occur in bound form within plant cell walls. The most common of these is didehydroferulic acid 23, which has been isolated from some plants of the Gramineae (53,54) and spinach cell cultures (7). While no such p-coumaric acid 2 derived dimer (i.e., C5-C5 linked) has ever been reported, cell walls of Lolium multiflorum contain another intriguing structural variation, namely 4,4 -dihydroxytruxillic acid 24 (5,55). 

---