Spectroscopy of the breaking bond: the diradical intermediate of the ring opening in oxazole

Abstract

Bond breaking is a challenging problem in both experimental and theoretical chemistry, due to the transient nature and multi-configurational electronic structure of dissociating molecules. We use anion photodetachment to probe the diradical interactions in the ring-opening reaction of oxazole and obtain a self-consistent picture of the breaking bond. Starting from the closed-shell cyclic molecule, the reaction is launched on the anion potential, as an attached electron cleaves a carbon-oxygen bond. In the photodetachment, two neutral potential regions are sampled. One corresponds to a completely dissociated bond, while the other - to the bond fragments separated by approximately 3 Å. At this chemically relevant distance, signatures of lingering through-space interactions between the radical centers are observed.

Unraveling the protonation site of oxazole and solvation with hydrophobic ligands by infrared photodissociation spectroscopy

“…[32][33][34][35][36] The geometric and spectroscopic properties of the planar Ox molecule have extensively been studied in its neutral S 0 state ( 1 A 0 ). [37][38][39][40][41][42][43][44][45][46] However, no experimental information is available for any neutral Ox-L n clusters, probably because the broad absorption spectrum prevents the application of convenient size-selective resonant ionization techniques. 47,48 Photoelectron spectra of Ox reveal that ionization into the planar ground electronic state ( 2 A 00 ) occurs by removal of an electron from a bonding p-orbital localized on the C4-C5 and O1-C2-N3 bonds.…”

HOCCO versus OCCO: Comparative spectroscopy of the radical and diradical reactive intermediates

“…This feature of anion photoelectron spectroscopy has been used to study a variety of exotic neutral species, including transient molecules, reactive intermediates, and even transition states, all of which are challenging to access using other methods. [1][2][3][4][5] Here, we present a comparative analysis of three glyoxal derivatives, the OHCCO and HOCCO radicals and the OCCO diradical, all three of which are generated via the photodetachment of the corresponding anions. The spectroscopy of HOCCO is reported for the first time, while the discussion of OCCO builds upon our recent brief report 6 of the discovery of this molecule.…”

Diradical Interactions in Ring-Open Isoxazole

“…The photoelectron spectra revealed signatures of both minima. 13 The corresponding neutral structures, 2 and 3 in Figure 1a, each possess their own state manifolds. These structures will be termed oxazole-2 and oxazole-3, respectively, while the cyclic ground-state structure 1 will be referred to for consistency, as oxazole-1.…”

“…Comparing the diradical structures of ring-open oxazole and isoxazole, we discuss two types of interactions between bond fragments, originally defined in the oxazole work: 13 the "through-space" and "through-bond" interactions. We expand their description and introduce a simple model, defining them in terms of Coulomb and bond integrals from the linear combination of atomic orbitalsmolecular orbital (LCAO-MO) theory.…”