Mechanisms of Photoelimination Reactions of Alkyl Benzohydroxamates

Abstract

Abstract— Photolysis at 254 nm of alkyl benzohydroxamates [C, H, CONHOR: R = CH3 H2CH3 CH(CH3)2, CH2C6H5 CH(CH3)C2H5 CH(CH3)‐n‐C6H13] in acetonitrile or hydrocarbon solvents gives benzamide. These reactions can be sensitized by benzophenone (at ca. 350 nm) and are quenched by cis‐piperylene. Racemization occurred when 2‐octyl (+)‐benzohydroxamate was irradiated in cyclohexane. These results are consistent with a mechanism involving a triplet biradical. Photolysis of phenyl benzohydroxamate [C6H5CONHOC6H5] and benzyl N‐methylbenzohydroxamate [C6H5CON‐(CH3)OCH2Q6H5] cannot be quenched with ris‐piperylene and appear to be singlet reactions.

Photodecomposition of N-hydroxyurea in argon matrices. FTIR and theoretical studies

“…32 These bands appear at 2681.0 and 2679.0 cm 21 after deuterium substitution, showing the same 2951 cm 21 deuterium shift within experimental error, as observed in the NH 2 OH molecule (H/D = 1.35). The 1613.4 cm 21 band appears in the region of the NH 2 bending vibration of NH 2 OH (1598.9 cm 21 ) and shows a very similar deuterium shift to dNH 2 in the monomer (2429 cm 21 shift is observed for the 1613.4 cm 21 band and 2428 cm 21 is reported for the 1598.9 cm 21 absorption). 32 The 1148.3 cm 21 band is observed in the vicinity of the NH 2 wagging vibration of the NH 2 OH molecule (1117.0 cm 21 ).…”

“…The broad band at ca. 2234 cm 21 is also observed in the vicinity of the n as NCO vibration of the HNCO monomer. The annealing experiments show the sensitivity of this band to the matrix temperature: the 2234 cm 21 band becomes more intense while the 2264 cm 21 one decreases upon the matrix annealing to 30 K for several minutes.…”

“…33 In the studied spectra the most characteristic band within 1 band set is a broad absorption at ca. 2264 cm 21 , in the region of n as NCO. After deuterium substitution a narrow band at 2222.8 cm 21 appears in this region and is assigned to the perturbed NCO antisymmetric stretching vibration of DNCO.…”

“…All new bands that appear in the spectra of photolysed matrices are assigned to HU photodissociation products and are collected in Table 1. New vibrational features are observed in the typical regions of water absorptions (3700-3600 cm 21 and 1650-1580 cm 21 ), isocyanic acid (HNCO) (2280-2200 cm 21 ), carbon monoxide (CO) (2160-2130 cm 21 ) and hydroxylamine (NH 2 OH) (3630-3600 cm 21 and 1150-1100 cm 21 ). The performed experiments allowed us to distinguish three main groups of bands, labelled as 1, 2a and 2b, which respond in different ways to the photolysis of HU/Ar matrices and to annealing processes.…”

“…Benzyl N-methylbenzohydroxamate was suggested to undergo photoelimination in the singlet state through a mechanism involving N-O bond cleavage. 21 In addition to the photolytic N-O bond scission, other mechanisms of the photolysis of hydroxamic acids have also been reported. The photoirradiation of selected naphthalenehydroxamic acids 22 suggests that photoirradiation of these compounds leads to acylaminoxyl radical generation and not to the scission of the N-O bond.…”