Chemiexcitation without the Peroxide Bond? Replacing Oxygen with other Heteroatoms

Conical Intersection in Chemiluminescence of Cyclic Peroxides

Chemiluminescence (CL) utilizing chemiexcitation for energy transformation is one of the most highly sensitive and useful analytical techniques. The chemiexcitation is a chemical process of a ground-state reactant producing an excited-state product, in which a nonadiabatic event is facilitated by conical intersections (CIs), the specific molecular geometries where electronic states are degenerated. Cyclic peroxides, especially 1,2-dioxetane/dioxetanone derivatives, are the iconic chemiluminescent substances. In this Perspective, we concentrated on the CIs in the CL of cyclic peroxides. We first present a computational overview on the role of CIs between the ground (S₀) state and the lowest singlet excited (S₁) state in the thermolysis of cyclic peroxides. Subsequently, we discuss the role of the S₀/S₁ CI in the CL efficiency and point out misunderstandings in some theoretical studies on the singlet chemiexcitations of cyclic peroxides. Finally, we address the challenges and future prospects in theoretically calculating S₀/S₁ CIs and simulating the dynamics and chemiexcitation efficiency in the CL of cyclic peroxides.

C2H5NO Isomers: From Acetamide to 1,2-Oxazetidine and Beyond

This work documents the properties of a number of isomers of molecular formula C₂H₅NO from the most stable, acetamide, through 1,2-oxazetidine and including even higher energy species largely of a dipolar nature. Only two of the isomers have been detected in emissions from the interstellar medium (ISM); possible further candidates are identified, and the likelihood of their being detectable is considered. In general, hardly any of these compounds have been discussed in the existing chemical literature, so this work represents an important contribution extending the canon of chemical bonding which can contribute to machine learning, providing a more exacting test of AI applications. The presence in the ISM of acetamide, CH₃C(O)NH₂, is the subject of current debate with no clear and obvious paths to its formation; it is shown that a 1,3-[H]-transfer from (E,Z)-ethanimidic acid, CH₃C(OH)=NH, is feasible in spite of an energy barrier of 130 kJ mol^–1. It is speculated that imidic acid can itself be formed from abundant precursors, H₂O and CH₃C≡N, in an acid-induced, water addition, autocatalytic reaction on water–ice grains. H₃CC≡NH₃CC≡NH⁺ + H₂OH₃CC(O⁺H₂)=NHH₃CC(OH)=NH + H₃O⁺

Elucidating the chemiexcitation of dioxetanones by replacing the peroxide bond with S–S, N–N and C–C bonds

Replacing the peroxide bond of dioxetanone prevents chemiluminescence by making its thermolysis energetically unfavorable and without a singlet chemiexcitation pathway.