Dear Aspirant,
Chemically, chloramphenicol is a simple structure consisting of a nitrobenzene ring bound with non-ionic chlorine.
It consists of two rare components one nitro group and one dichloroacetyl group.
The molecule has two asymmetric carbon atoms therefore four optical isomers are possible. Of these isomers one is antibioticly active.
Chloramphenicol is  broad antibiotic active against both gram-positive and gram-negative bacteria.

I hope this information helps you

All the best