“…Figure presents the transient resonance Raman spectrum obtained for the 4-ethoxyphenylnitrenium ion obtained under similar conditions as the 4-methoxyphenylnitrenium ion in Figures and . Comparison of experimental vibrational frequencies to those predicted from density functional theory (DFT) or ab initio calculations forprobable photoproduct species has been used successfully to identify and assign time-resolved infrared (TRIR) and time-resolved resonance Raman (TR 3 ) spectra to arylnitrenium ions, arylnitrenes, and arylnitrene photoproducts. ,− , A similar methodology will be used to assign the TR 3 spectra observed in Figures −3. We note that the lifetimes of arylnitrenium ions measured previously by transient absorption or TRIR experiments showed no discernible difference when done in O 2 - and N 2 -purged solutions. , Thus, we do not expect that removal of O 2 is likely to make any difference in the observed transient Raman spectra shown in Figures −3.…”
Section: Resultsmentioning
confidence: 99%
“…Samples of the precursor compound (4-methoxyphenyl azide or 4-ethoxyphenyl azide) were prepared with concentrations of about 2.5 mM in a 60% water/40% acetonitrile mixed solvent by volume with an acetate buffer (2 mM) and a pH of 3.5. The transient resonance Raman spectra were obtained using an experimental apparatus and methods detailed previously so only a brief description will be presented here. ,, The harmonics of a pulsed Nd:YAG laser and their hydrogen Raman shifted laser lines were used for the pump (266 nm) and probe (320 nm) excitation wavelengths in the transient Raman experiments. An optical time-delay of approximately 10 ns between the pump and probe pulses was used in the experiments.…”
Section: Experimental and Computational Sectionmentioning
This paper presents a transient resonance Raman and density functional theory study of 4-methoxyphenylnitrenium and 4-ethoxyphenylnitrenium ions in a largely aqueous environment. The transient Raman bands observed in conjunction with the (U)BPW91/cc-PVDZ calculation results indicates these nitrenium ions are singlet state species. Both the 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions have significant iminocyclohexadienyl character to a degree very similar to that previously found for the 2-fluorenylnitrenium ion. The 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions also have significant oxocarbocation character and this influences both their properties and chemical reactivity. We compare the properties of the 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions to those previously found for other arylnitrenium ions.
“…Figure presents the transient resonance Raman spectrum obtained for the 4-ethoxyphenylnitrenium ion obtained under similar conditions as the 4-methoxyphenylnitrenium ion in Figures and . Comparison of experimental vibrational frequencies to those predicted from density functional theory (DFT) or ab initio calculations forprobable photoproduct species has been used successfully to identify and assign time-resolved infrared (TRIR) and time-resolved resonance Raman (TR 3 ) spectra to arylnitrenium ions, arylnitrenes, and arylnitrene photoproducts. ,− , A similar methodology will be used to assign the TR 3 spectra observed in Figures −3. We note that the lifetimes of arylnitrenium ions measured previously by transient absorption or TRIR experiments showed no discernible difference when done in O 2 - and N 2 -purged solutions. , Thus, we do not expect that removal of O 2 is likely to make any difference in the observed transient Raman spectra shown in Figures −3.…”
Section: Resultsmentioning
confidence: 99%
“…Samples of the precursor compound (4-methoxyphenyl azide or 4-ethoxyphenyl azide) were prepared with concentrations of about 2.5 mM in a 60% water/40% acetonitrile mixed solvent by volume with an acetate buffer (2 mM) and a pH of 3.5. The transient resonance Raman spectra were obtained using an experimental apparatus and methods detailed previously so only a brief description will be presented here. ,, The harmonics of a pulsed Nd:YAG laser and their hydrogen Raman shifted laser lines were used for the pump (266 nm) and probe (320 nm) excitation wavelengths in the transient Raman experiments. An optical time-delay of approximately 10 ns between the pump and probe pulses was used in the experiments.…”
Section: Experimental and Computational Sectionmentioning
This paper presents a transient resonance Raman and density functional theory study of 4-methoxyphenylnitrenium and 4-ethoxyphenylnitrenium ions in a largely aqueous environment. The transient Raman bands observed in conjunction with the (U)BPW91/cc-PVDZ calculation results indicates these nitrenium ions are singlet state species. Both the 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions have significant iminocyclohexadienyl character to a degree very similar to that previously found for the 2-fluorenylnitrenium ion. The 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions also have significant oxocarbocation character and this influences both their properties and chemical reactivity. We compare the properties of the 4-methoxyphenylnitrenium and the 4-ethoxyphenylnitrenium ions to those previously found for other arylnitrenium ions.
“…Figure shows an expanded view of the transient resonance Raman spectrum of the 4-acetamidophenylnitrenium ion presented in Figure . Comparison of the experimental band vibrational frequencies and intensities to those predicted from density functional theory (DFT) or ab initio calculations for probable photoproduct species have been used to successfully assign time-resolved infrared (TRIR) and time-resolved resonance Raman (TR 3 ) spectra to arylnitrenium ions, arylnitrenes, and other chemical intermediates. ,− ,− A similar methodology will be used to assign the TR 3 spectra shown in Figures and . 1 Examples of a typical 266 nm pump-only spectrum in the probe wavelength region (A), a 320 nm probe-only Raman spectrum (B), a pump−probe spectrum (C), and the resulting transient resonance Raman spectrum (D) of the 4-acetamidophenylnitrenium ion.…”
Section: Resultsmentioning
confidence: 99%
“…Samples of 4-acetamidophenyl azide were prepared with concentrations of about 2.5 mM in a 60% water/40% acetonitrile mixed solvent by volume with an acetate buffer (2 mM) and a pH of 3.5. The transient resonance Raman spectrum was obtained using an experimental apparatus and methods described elsewhere, ,,− so only a short description will be given here. The harmonics of a pulsed Nd:YAG laser and its hydrogen Raman-shifted laser lines provided the pump (266 nm) and probe (320 nm) excitation wavelengths for the transient Raman experiments.…”
Section: Experimental and Computational Sectionmentioning
This paper reports a transient resonance Raman and density functional theory study of the 4-acetamidophenylnitrenium ion in a mostly aqueous solvent. The transient Raman bands combined with results from density functional theory calculations indicate that the spectrum should be assigned to the singlet state of the 4-acetamidophenylnitrenium ion. The 4-acetamidophenylnitrenium ion was found to have a substantial iminocyclohexadienyl character comparable to previously studied para-phenyl-substituted phenylnitrenium ions and noticeable charge on both the acetamido and nitrenium moieties. The structure and properties of the 4-acetamidophenylnitrenium ion are compared to those of other arylnitrenium ions. We briefly discuss the chemical reactivity and selectivity of the para-acetamido-substituted phenylnitrenium ions compared to para-phenyl- or para-alkoxy-substituted phenylnitrenium ions.
“…The ns-TR 3 measurements were done using an apparatus described previously in ref . A 266 nm pump and 416 and 341.5 nm probe excitation wavelengths were used in the experiments and generated from the harmonics of a 10 Hz pulsed Nd:YAG laser and/or their hydrogen Raman-shifted laser lines.…”
Section: Experimental and Computational Methodsmentioning
[reaction; see text] Picosecond and nanosecond time-resolved resonance Raman (TR(3)) spectroscopy was employed to investigate the deprotonation/ionization reaction of p-hydroxyacetophenone (HA) after ultraviolet photolysis in water solution. The TR(3) spectra in conjunction with density functional theory (DFT) calculations were used to characterize the structure and dynamics of the excited-state HA deprotonation to form HA anions in near neutral water solvent. DFT calculations based on a solute-solvent intermolecular H-bonded complex model containing up to three water molecules were used to evaluate the H-bond interactions and their influence on the deprotonation reaction and the structures of the intermediates. The deprotonation reaction was found to occur on the triplet manifold with a planar H-bonded HA triplet complex as the precursor species. The HA triplet species is generated within several picoseconds and then decays with a approximately 10 ns time constant to produce the HA triplet anion species after 267 nm photolysis of HA in water solution. The triplet anion species was observed to decay with a time constant of about 90 ns into the ground-state anion species that was found to have a lifetime of about 200 ns. The DFT calculations on the H-bonded complexes of the anion triplet and ground-states species suggest that these anion species are H-bonded complexes with planar quinonoidal structures containing two water molecules H-bonded, respectively, with oxygen lone pairs of the carbonyl and deprotonated hydroxyl moieties. A deactivation scheme of the photoexcited HA in regard to the deprotonation reaction in neutral water solutions was proposed. With the above dynamic and structural information available, we briefly discuss the possible implications of the model HA photochemistry in water solutions for the photodeprotection reactions of related p-HP phototrigger compounds in aqueous solutions.
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