Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theory.
4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.
Kanawati
Basem
B
Max-Planck Institute for Chemistry, Atmospheric Chemistry Division, PO Box 3060, D-55020 Mainz, Germany. kanawati.b@gmail.com
Joniec
Seweryn
S
Winterhalter
Richard
R
Moortgat
Geert K
GK
D000838:Anions / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D005030:Ethylenes / Q000737:chemistry; D006358:Hot Temperature; D006878:Hydroxides / Q000737:chemistry; D007651:Keto Acids / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D000432:Methanol / Q000737:chemistry; D008958:Models, Molecular; D010421:Pentanoic Acids / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods*; D014835:Volatilization; D014867:Water / Q000737:chemistry
C531471:4-oxopentanoic acid; D000838:Anions; D005030:Ethylenes; D006878:Hydroxides; D007651:Keto Acids; D007659:Ketones; D010421:Pentanoic Acids; D012997:Solvents; D014867:Water; D002245:Carbon Dioxide; C031356:hydroxide ion; C008223:ketene; D000432:Methanol