In the box I delivered a chemical compound (5)
I believe the answer is:
oxide
'a chemical compound' is the definition.
(oxide is a kind of chemical compound)
'in the box i delivered' is the wordplay.
'in' says the answer is hidden in the clue.
'OXIDE' can be found hidden inside 'box i delivered'.
(Other definitions for oxide that I've seen before include "Rust is iron -" , "Compound of two elements, one with atomic number 8" , "Rust, for instance" , "Eg, rust" , "Compound of oxygen and one other element" .)