3',5'-Dimethoxybenzoin (DMB) is an important photoremovable protecting group. The primary photoreactions of DMB acetate and fluoride following photoexcitation by a subpicosecond laser flash were investigated by pump probe spectroscopy. The primary photoproduct is identified as a preoxetane biradical intermediate that decays by different pathways depending on solvent polarity. In polar solvents, the biradical decays by releasing acetate or fluoride with a lifetime of about 2 ns. Thus, DMB is an excellent protecting group for the investigation of fast processes such as protein folding.
COBISS.SI-ID: 28844549
Dihydrogen trioxide is formed nearly quantitatively in the low-temperature (-70 oC) methyltrioxorhenium(VII) – catalysed transformation of silyl hydrotrioxides an some acetal hydrotrioxides in various solvents, as confirmed by 1H and 17O NMR spectroscopy. The calculated energetics for the catalytic cycle, using H3SiOOOH as a model system, is consistent with the experimental observations. This type of transformation appears to represent a convenient and general method for the preparation of HOOOH, suitable for further studies, without the interfering presence of hydrotrioxides and HOOOH.
COBISS.SI-ID: 29900293
Photolysis of 2-fluoro-1,2-diphenylethanone in MeCN or MeOH produces 2-phenylbenzofuran. In trifluoroethanol only 3% of 2-phenylbenzofuran and 13% of the a-ketocation solvent adduct are formed. The observed triplet state in nanosecond experiment at low temperature has been confirmed in femtosecond experiment. The triplet is formed quite fast at 370 nm (rise time 4.5 ps in acetonitrile and 22 ps in trifluoroethanol) and is stable up to 1.9 ns (a lifetime of 20 ns has been determined by quenching experiments with naphthalene).
COBISS.SI-ID: 29743621
We found that the hydrotrioxide of benzaldehyde is formed in an exothermic reaction involving the 1,3-dipolar insertion of ozone into the C-H bond of benzaldehyde. This intermediate forms benzoic acid and singlet oxygen. Because of the low barrier for the formation of hydrotrioxide this intermediate is not observed. A theoretical investigation of the involvement of still another intermediate, a cyclic tetraoxide formed as a primary product in the 1,3-dipolar cycloaddition of ozone to the carbonyl group of the aldehyde was also investigated.
COBISS.SI-ID: 30098181
CCSD(T) and MP2 calculations have been carried out to determine the relative stabilities of the protonation sites in HOOOH. We have shown that the terminally protonated species, HOOO(H)H+, is thermodynamically favored and is stabilized by water solvent molecules. The formation of the protonated species provides the lowest energy decomposition pathway for HOOOH. All attempts to detect HOOO(H)H+ intermediate by 17O NMR spectroscopy were unsuccessful, which also implies a rapid decomposition of this species to form the thermodynamically favored reaction products of O2 and water.
COBISS.SI-ID: 34295813