Adiabatic and Nonadiabatic Bond Cleavages in Norrish Type I Reaction

Abstract

One of the fundamental photoreactions for ketones is Norrish type I reaction, which has been extensively studied both experimentally and theoretically. Its α bond-cleavage mechanisms are usually explained in an adiabatic picture based on the involved excited-state potential energy surfaces, but scarcely investigated in terms of a nonadiabatic picture. In this work, the S(1) α bond-cleavage reactions of CH(3)OC(O)Cl have been investigated by using the CASSCF and MRCI-SD calculations, and the ab initio based time-dependent quantum wavepacket simulation. The numerical results indicate that the photoinduced dissociation dynamics of CH(3)OC(O)Cl could exhibit strong nonadiabatic bond-fission characteristics for the S(1) α C-Cl bond cleavage, while the dynamics of the S(1) α C-O bond cleavage is mainly of adiabatic characteristics. This nonadiabatic mechanism for Norrish type I reaction of CH(3)OC(O)Cl is uncovered for the first time. The quantum wavepacket dynamics, based on the reduced-dimensional coupled potential energy surfaces, to some extent illustrates the significance of the nonadiabatic effect in the transition-state region on the dynamics of Norrish type I reaction.

Photoinduced Formation of H-Bonded Ion Pair in HCFC-133a

“…Finally, Cl – release can in principle take place in related compounds, as some chloro-carbonyl compounds, − as long as (i) the R-CH 2 and Cl open-shell doublet radicals are present not very far from each other, during photodissociation of the parent compound, and (ii) the excitation energy is high enough to achieve the ion pair channel.…”

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

“…Increasing interest in photochemistry is often attributed to the ability to access radical intermediates that are otherwise difficult or impossible to obtain by classical chemistry but that can achieve unique chemical reactions complementary to two-electron processes [72][73][74][75][76][77]. However, the adoption of photochemistry into the toolbox of the synthetic organic chemist has been hindered by three phenomena: i) simple organic-molecule targets typically do not absorb (or have very small extinction coefficients for) visible light, which is among the most abundant in the solar distribution [78,79], instead absorbing only short wavelengths of UV light, ii) the photoexcitation of simple organic molecules by requisite high-energy UV photons populates higher-order excited states that undergo uncontrolled photodecomposition, such as Norrish-type cleavage reactions [80] and 1,5-HAT [81] and iii) the excited state of the simple organic molecule target can possess an ultrashort lifetime [82] that precludes photochemistry in favor of photophysical or nonradiative deactivation, e.g., fluorescence or internal conversion (IC).…”

Quantum Chemical Investigation on Photochemical Reactions of Nonanoic Acids at Air–Water Interface

“…Table collects TD-B3LYP-D3 and B3LYP-D3 computed vertical excitation energies of NA and its two water complexes to the lowest two excited states, that is, S 1 and T 1 . Electronic structure analysis shows that these two singlet and triplet states are of n π* character as found in many similar saturated carbonyl compounds. ,,− In addition, it can be found that water hydration has small influence on vertical and adiabatic excitation energies to these two singlet and triplet states. The vertical and adiabatic excitation energies of water-hydrated NA molecules are merely blue-shifted a little compared with those of isolated NA molecule.…”

“…Therefore, NA will first hop to the T 1 state via the S 1 → T 1 intersystem crossing at the Franck−Condon region as already observed in many similar carbonyl compounds. 34,49,52,54 In the T 1 state, the CO bond fission of isolated NA from its T 1 minimum 1* is still inefficient because the T 1 energy of the TS(1−2) transition state, that is, 105.2 kcal/mol at B3LYP-D3 level, is close to available total energy (exp. 106 kcal/mol; red lines in Figure 5).…”