Chemical benefit is rejected - better go to ground (8)
I believe the answer is:
sulphide
'chemical' is the definition.
(I've seen this before)
'rejected better go to ground' is the wordplay.
'rejected' says the letters should be written in reverse.
'better' becomes 'plus' (I can't justify this - if you can you should believe this answer much more).
'go to ground' becomes 'hide' (I've seen this before).
'plus' reversed gives 'sulp'.
'sulp'+'hide'='SULPHIDE'
'benefit is' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sulphide that I've seen before include "compound" , "chemical" .)