Conformational Landscape, Infrared Characterization, and UV-Induced Reactivity of 3-Chloromethyl-5-(3-Methoxyphenyl)-1,2,4-Oxadiazole Isolated in a Nitrogen Matrix

İsa Sıdır; António J. L. Jesus; Rui Fausto

doi:10.53941/ps.2026.100022

Abstract

In this study, we present a comprehensive analysis of the conformational landscape, vibrational properties and photochemistry of monomeric 3-chloromethyl -5-(3-methoxyphenyl)-1,2,4-oxadiazole (CMPO). This molecule can adopt eight different conformers, but only four of these (the skew conformers, with the chlorine atom tilted out of the oxadiazole ring plane) have significant populations in the gas phase. Comparison of the infrared spectrum of monomers of CMPO isolated in solid N₂ at 15 K with B3LYP/6-311++G(d,p) vibrational calculations, supports the presence of the four skew conformers in the as-deposited low-temperature N₂ matrix. UV measurements in various solvents reveal an intense absorption near λ = 255 nm, which TD-DFT calculations assign primarily to a S₀ →S₂ π → π* transition. UV irradiations of the matrix-isolated compound, using both narrowband (λ = 255 nm) and broadband (λ > 220 nm) light, induce N–O bond cleavage and ring opening, yielding carbodiimide (the favored species) and cyanamide as the isomerization photoproducts. No spectroscopic evidence of diazirine, nitrilimine, or 1,3,4-oxadiazole intermediates was detected. Photodecomposition also occurs, leading to the formation of isocyanate and 2-chloroacetonitrile. All the photoproduced species were identified by comparing the emerging IR bands with the computed vibrational spectra of the putative photoproducts.

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