Premium
Photodissociation of protonated β‐diketones in the gas phase
Author(s) -
Reents W. D.,
Murray K. J.,
Freiser B. S.
Publication year - 1980
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210151005
Subject(s) - protonation , photodissociation , chemistry , photochemistry , absorption spectroscopy , absorption (acoustics) , ion , medicinal chemistry , materials science , organic chemistry , physics , quantum mechanics , composite material
The gas phase photodissociation spectra of four protonated β‐diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4‐pentanedione was observed to undergo the photodissociation process [C 5 H 9 O 2 ] + +hν → [CH 3 CO] + +C 3 H 6 O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4‐hexanedione was observed to undergo the photodissociation processes [C 6 H 11 O 2 ] + +hν → [CH 3 CO] + +C 4 H 8 O and [C 6 H 11 O 2 ] + +hν → [C 2 H 5 CO] + +C 3 H 6 O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3‐methyl‐2,4‐pentanedione was observed to undergo the photodissociation process [C 6 H 11 O 2 ] + +hν → [CH 3 CO] + +C 4 H 8 O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1‐trifluoro‐2,4‐pentanedione was observed to undergo the photodissociation process [C 5 H 6 F 3 O 2 ] + +hν → CF 3 H+[C 4 H 5 O 2 ] + with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH 3 CO] + and [C 2 H 5 CO] + produced photochemically with the first three ions react to regenerate the protonated β‐diketone leading to a photostationary state. Photodissociation of the protonated alkyl β‐diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1‐trifluoro‐2,4‐pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented.