Dissociative Ionization and Thermal Decomposition of Cyclopentanone

Abstract

Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2H4, and C2H5, leading to daughter ions at m/z 56 and 55. Exploring the C5H8O. + potential energy surface reveals hydrogen tunneling to play an important role in low‐energy decarbonylation and probably also in the ethene‐loss processes, yielding 1‐butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl‐radical loss and a second ethene‐loss channel, respectively. A statistical Rice–Ramsperger–Kassel–Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed‐shell pyrolysis products, namely 1,3‐butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass‐selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies.

Nitrogen matters: the difference between PANH and PAH formation

“…This approach has been used in the identification and characterization of elusive reactive intermediates, 28 which help unveil complex reaction mechanisms in diverse reactive environments. [29][30][31] Ab initio calculations and kinetic modeling are performed to explore the potential energy surface and rationalize the experimental data. 32 Contrary to our expectations, based primarily on naphthalene formation in the analogous phenyl + vinylacetylene reaction, 23 we did not detect quinoline and argue that it may only be a minor reaction product.…”

Determination of highest occupied molecular orbital and cationic structures of cyclopentanone using high‐resolution vacuum ultraviolet mass‐analyzed threshold ionization mass spectrophotometry

“…1,2 In addition, since CP is a precursor for synthesizing fragrances, pharmaceuticals, and biologically active compounds, 3,4 its conformational structure and conformation-dependent reactivity have been investigated by various means. [5][6][7][8][9][10][11][12] It is known that CP exists at equilibrium as a twisted conformer with C 2 symmetry, and conformer interconversion occurs via pseudorotational or twisting motions. 5,6 Furthermore, it was proposed that interconversion between the twisted conformers occurs preferentially along the pseudorotational coordinate associated with the envelope transition conformation at the lower barrier of approximately 750 cm À1 rather than via the planar hilltop conformation (C 2V symmetry) at the higher barrier of approximately1400 cm À1 .…”

“…Subsequently, photoelectron spectroscopy and laser-induced ionization/dissociation techniques have been performed with the aim of understanding the mechanism of fragmentation via ring opening for the CP ion. [7][8][9][10][11][12] However, different dissociation pathways corresponding to the m/z = 56 products (C 3 H 4 O + and C 4 H 8 + ) of the CP cation were proposed. Thus, the details of the ionization/dissociation mechanisms regarding the formation of a CP fragment ion remain poorly understood.…”

“…Cyclopentanone (CP), which can be easily synthesized from furfural via one‐step hydrogenation, has received significant attention from the alternative fuel industry 1,2 . In addition, since CP is a precursor for synthesizing fragrances, pharmaceuticals, and biologically active compounds, 3,4 its conformational structure and conformation‐dependent reactivity have been investigated by various means 5–12 . It is known that CP exists at equilibrium as a twisted conformer with C 2 symmetry, and conformer interconversion occurs via pseudorotational or twisting motions 5,6 .…”

“…Furthermore, it was proposed that interconversion between the twisted conformers occurs preferentially along the pseudorotational coordinate associated with the envelope transition conformation at the lower barrier of approximately 750 cm −1 rather than via the planar hilltop conformation ( C 2V symmetry) at the higher barrier of approximately1400 cm −1 . Subsequently, photoelectron spectroscopy and laser‐induced ionization/dissociation techniques have been performed with the aim of understanding the mechanism of fragmentation via ring opening for the CP ion 7–12 . However, different dissociation pathways corresponding to the m / z = 56 products (C 3 H 4 O + and C 4 H 8 + ) of the CP cation were proposed.…”