Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (<b>1</b>), 2,1,3-benzothiaselenazolium (<b>3</b>), and 1,2,3-benzodiselenazolium (<b>4</b>) (Herz cations), namely, [<b>1</b>]­[BF₄], [<b>1</b>]­[SbCl₆], [<b>3</b>]­[BF₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[SbCl₆], and [<b>4</b>]­[GaCl₄], were prepared from the corresponding chlorides and NaBF₄, GaCl₃, or SbCl₅. It was found that [<b>1</b>]­[SbCl₆] and [<b>3</b>]­[SbCl₆] spontaneously transform in MeCN solution to [<b>1</b>]₃[SbCl₆]₂[Cl] and [<b>3</b>]₃[SbCl₆]₂[Cl], respectively. [<b>1</b>]­[BF₄], [<b>1</b>]₃[SbCl₆]₂[Cl], [<b>3</b>]­[BF₄], [<b>3</b>]₃[SbCl₆]₂[Cl], and [<b>4</b>]­[GaCl₄] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF₄]⁻ and [GaCl₄]⁻ salts as well as [<b>1</b>]­[GaCl₄], [<b>2</b>]­[GaCl₄], [<b>3</b>]­[GaCl₄], [<b>3</b>]­[Cl], and [<b>4</b>]­[Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph₃Sb and characterized by EPR. Cations <b>1</b>–<b>4</b> and radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b> were investigated computationally at the density functional theory (DFT) and second-order Møller–Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of <b>1</b>–<b>4</b>; an increase in the basis set size to cc-pVQZ results in only minor changes. For both <b>1</b>–<b>4</b> and <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>, the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals <b>1</b>^<b>•</b>–<b>4</b>^<b>•</b>. For the cations <b>1</b>–<b>4</b>, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from −5.5 ppm to −6.6 ppm for the carbocycles, and from −14.4 ppm to −15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers <b>[1</b>^<b>•</b><b>]</b>₂–[<b>4</b>^<b>•</b><b>]</b>₂ revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase

2‑Hydroxyterpenylic Acid: An Oxygenated Marker Compound for α‑Pinene Secondary Organic Aerosol in Ambient Fine Aerosol

An oxygenated MW 188 compound is commonly observed in substantial abundance in atmospheric aerosol samples and was proposed in previous studies as an α-pinene-related marker compound that is associated with aging processes. Owing to difficulties in producing this compound in sufficient amounts in laboratory studies and the occurrence of isobaric isomers, a complete assignment for individual MW 188 compounds could not be achieved in these studies. Results from a comprehensive mass spectrometric analysis are presented here to corroborate the proposed structure of the most abundant MW 188 compound as a 2-hydroxyterpenylic acid diastereoisomer with 2<i>R</i>,3<i>R</i> configuration. The application of collision-induced dissociation with liquid chromatography/electrospray ionization-ion trap mass spectrometry in both negative and positive ion modes, as well as chemical derivatization to methyl ester derivatives and analysis by the latter technique and gas chromatography/electron ionization mass spectrometry, enabled a comprehensive characterization of MW 188 isomers, including a detailed study of the fragmentation behavior using both mass spectrometric techniques. Furthermore, a MW 188 positional isomer, 4-hydroxyterpenylic acid, was tentatively identified, which also is of atmospheric relevance as it could be detected in ambient fine aerosol. Quantum chemical calculations were performed to support the diastereoisomeric assignment of the 2-hydroxyterpenylic acid isomers. Results from a time-resolved α-pinene photooxidation experiment show that the 2-hydroxyterpenylic acid 2<i>R</i>,3<i>R</i> diastereoisomer has a time profile distinctly different from that of 3-methyl-1,2,3-butanetricarboxylic acid, a marker for oxygenated (aged) secondary organic aerosol. This study presents a comprehensive chemical data set for a more complete structural characterization of hydroxyterpenylic acids in ambient fine aerosol, which sets the foundation to better understand the atmospheric fate of α-pinene in future studies