what is the content of the sunflower seed shells that caused the grass to die?

Question

i got the idea from one of your answers in the question of some people.

Answer 1

Sunflowers are allelopathic plants, this means they shed poisons on the floor to avoid competition on nutrients by other species, just like eucalyptus does.
The chemical compounds are:
phenols, terpens, flavons, alkaloids and others

Answer 2

Are we talking seeds that you plant or did you chew a bunch and spit them on your lawn and it caused a dead spot? For the Former, the 1st answer is good, the later would be good old salt