Quantum-chemical Study of the Fragmentation Pathways of Chloramphenicol

The fragmentation mechanism of chloramphenicol (CAP) was studied with bond dissociation energy (BDE) calculation. The geometries of CAP and the BDEs of the correlative bonds in gas phase at 298.15 K were analyzed by density functional theory (DFT) at ROB3LYP /6-311 ++ G (2d, 2p)//B3LYP/ 6-31G (d) level. Based on the comparison of the calculated BDEs, the structure and the origin of each fragment ion appeared in the mass spectra of CAP were determined, and then the whole fragmentation pathway was deduced. The results indicate that the parent ion of CAP forms m/z 254, 192 and 157 fragment ions with the Cl, CHO, C₂H₂O and NH₂COCHCl₂ neutral groups lost. And there is a certain correlation between the relative abundances and the energy gaps (△E) of frontier molecular orbitals of the fragment ions. The results also indicate that the BDE analysis is a useful way to elucidate the fragmentation pathway of organic molecule.