Low-Lying Electronic States of Cyclopentadienone

Abstract

We report a combined experimental and theoretical study of the low-lying electronic states of cyclopentadienone (C5H4O). The cyclopentadienone anion (C5H4O(-)) was generated in the gas phase via reaction of atomic oxygen radical anions (O(-)) with cyclopentanone (C5H8O). Photoelectron imaging was used to gain access to the first three electronic states of C5H4O, including the X (1)A1 ground state and the (3)B2 and (3)A2 excited states. The first two state assignments are supported by the Franck-Condon simulations of the vibrational progressions observed in the X (1)A1 and (3)B2 bands in the photoelectron spectra. The adiabatic electron affinity of cyclopentadienone in the ground state is determined to be EA(X (1)A1) = 1.06 ± 0.01 eV, and the corresponding values for the first two excited states are EA((3)B2) = 2.56 ± 0.02 eV and EA((3)A2) = 3.45 ± 0.01 eV. These experimental determinations are in excellent agreement with the CCSD(T) theory predictions, lending further confidence to the above state assignments. On the basis of these results, the lowest singlet-triplet splitting (between the X (1)A1 and (3)B2 states) in cyclopentadienone is ΔES-T = 1.50 ± 0.02 eV.

Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol

“…The C–H bond energy of the parent cyclopentadiene is 83 kcal mol –1 ; consequently, we expect that loss of H from hydroxyl-cyclopentadiene to generate the hydroxyl-cyclopentadienyl radical ( m / z 81) will require approximately 80 kcal mol –1 . Further decomposition of the C 5 H 4 OH radical leads to H atom and to the well-characterized ,− cyclopentadienone, C 5 H 4 O ( m / z 80).…”

“…Further decomposition of the C 5 H 4 OH radical leads to H-atom and to the well characterized48,[74][75][76][77] cyclopentadienone, C 5 H 4 =O (m/z 80).Fig. 5 is the 118.2 nm PIMS that is observed when a sample of catechol is heated in a pulsed, 1 mm SiC micro-reactor.…”

The ionisation energy of cyclopentadienone: a photoelectron–photoion coincidence study

“…The highest occupied (a 2 symmetry) molecular orbital is localised on the carbon atoms in the five membered ring, qualitatively resembling an out-of-phase combination of ethylenelike bonding π orbitals. A recent negative ion electron photodetachment study [9] indicates that the lowest state of the anion (and hence the lowest 'unoccupied orbital') has b 1 symmetry (π * ) and calculations suggest that this orbital is delocalised over the entire system. Figure 1 shows a summary of the molecular orbitals calculated for the ground state neutral ( X 1 A 1 ) species of C 5 H 4 =O on Hartree-Fock/ANO0 basis set [10].…”

Photodissociation of the Product from a Transition-Metal Center Allows the Catalytic Cycle to Proceed: The Rhodium(I)-Catalyzed [2+2+1] Carbonylative Cycloaddition of Diynes

“…The dual dπ–pπ* back-donation from a metal to the CPD (two enones) and the 4π-antiaromaticitiy properties of CPDs leads to the strong coordination of the CPD to a metal (Scheme ). Therefore, the catalytic synthesis of CPDs via the [2+2+1] carbonylative cycloaddition of two alkynes has not been effective, even when a rhodium complex is used as a catalyst, which typically functions well in versatile types of carbonylative cycloaddition transformations . The study presented here also affords an accessible and convenient method for the catalytic synthesis of CPDs (Scheme ).…”