Kawa Constituents- — Hansel 
307 
H 
Fig. 12. Mass spectrum of kawain (Pailer et al., 1965). 
agreement with observations on other open 
chain enone systems. Since the enone system 
exists in the ring, where it is rigidly maintained 
in the energetically favorable s -trans conforma- 
tion, the position and magnitude of the absorp- 
tion change only insignificantly when we go 
to the corresponding open chain enone system. 
In other words, we can compare PSS with cis- 
crotonic acid and dihydromethysticin (DHM) 
with tetrahydromethystinic acid (Fig. 15). 
If we substitute the ring of DH-MTL with 
a phenylethyl or with a styryl radical instead of 
