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A synchrotron based vacuum ultraviolet absorption spectrum for γ-pyrone has been interpreted in terms of singlet excited electronic states using a variety of coupled cluster, configuration interaction, and density functional calculations. The extremely weak spectral onset at 3.557 eV shows eight vibrational peaks, which following previous analyses, are attributed to a forbidden 1A2 state. A contrasting broad peak with a maximum at 5.381 eV has a relatively high cross-section of 30 Mb; this arises from three overlapping states, where a 1A1 state dominates over progressively weaker 1B2 and 1B1 states. After fitting the second band to a polynomial Gaussian function and plotting the regular residuals over 20 vibrational peaks, we have had limited success in analyzing this fine structure. However, the small separation between these three states clearly shows that their vibrational satellites must overlap. Singlet valence and Rydberg state vibrational profiles were determined by configuration interaction using the CAM-B3LYP density functional. Vibrational analysis using both the Franck–Condon and Herzberg–Teller procedures showed that both procedures contributed to the profiles. Theoretical Rydberg states were evaluated by a highly focused CI procedure. The superposition of the lowest photoelectron spectral band on the vacuum ultraviolet spectrum near 6.4 eV shows that the 3s and 3p Rydberg states based on the 2B2 ionic state are present; those based on the other low-lying ionic state (X2B1) are destroyed by broadening; this is a dramatic extension of the broadening previously witnessed in our studies of halogenobenzenes. [ABSTRACT FROM AUTHOR]

Application of the [1,2]-Wittig rearrangement and cyclisation approach to 3-arylphthalides has been evaluated for the synthesis of three bioactive natural products. While this is successful in the case of crycolide, providing the second synthesis of this compound, the more sterically demanding targets isopestacin and cryphonectric acid prove not to be amenable to this approach, with the 2,6-disubstituted aryl groups causing the failure of the rearrangement and alkylation steps, respectively. Direct oxidation of the substituted benzhydrols resulting from [1,2]-Wittig rearrangement using MnO2 provides a new route to 3-aryl-3-hydroxyisoindolinones, and this method has been used in the synthesis of two 3-aryl-3-benzyloxyisoindolinone anticancer agents. [ABSTRACT FROM AUTHOR]

The title compound and its hydroxymethyl precursor have been fully characterised for the first time. The IR spectra, fully assigned 1H and 13C NMR spectra, and X-ray structures are presented for both compounds. Both compounds form hydrogen-bonded dimers in the crystal structures. [ABSTRACT FROM AUTHOR]

A synchrotron-based vacuum ultraviolet absorption spectrum (VUV) of quadricyclane (QC) is reported with energies up to 10.8 eV. Extensive vibrational structure has been extracted from the broad maxima by fitting short energy ranges of the VUV spectrum to high level polynomial functions and processing the regular residuals. Comparison of these data with our recent high-resolution photoelectron spectral of QC showed that this structure must be attributed to Rydberg states (RS). Several of these appear before the valence states at higher energies. Both types of states have been calculated by configuration interaction, including symmetry-adapted cluster studies (SAC-CI) and time dependent density functional theoretical methods (TDDFT). There is a close correlation between the SAC-CI vertical excitation energies (VEE) and both Becke 3-parameter hybrid functional (B3LYP), especially Coulomb-attenuating method-B3LYP determined ones. The VEE for several low-lying s-, p, d-, and f-RS have been determined by SAC-CI and adiabatic excitation energies by TDDFT methods. Searches for equilibrium structures for 11,3A2 and 11B1 states for QC led to rearrangement to a norbornadiene structure. Determination of the experimental 00 band positions, which show extremely low cross-sections, has been assisted by matching features in the spectra with Franck–Condon (FC) fits. Herzberg–Teller (HT) vibrational profiles for the RS are more intense than the FC ones, but only at high energy, and are attributed to up to ten quanta. The vibrational fine structure of the RS calculated by both FC and HT procedures gives an easy route to generating HT profiles for ionic states, which usually require non-standard procedures. [ABSTRACT FROM AUTHOR]

A simplified synthesis of the title compound is reported and its 1H and 13C NMR data are fully assigned including determination of H–H and C–H coupling constants. Its X-ray structure has been determined for the first time. NMR data are also presented for the oxygen analogue. [ABSTRACT FROM AUTHOR]

A synchrotron-based photoionization spectrum up to 27 eV represents a considerable improvement in resolution over early He(I) and He(II) spectra. Symmetry-adapted coupled cluster calculations of the ionic state sequence give the sequence of state vertical ionization energies (VIE) as 12B2 < 12B1 < 12A2 < 22B1 < 12A1. Generally, these symmetry-adapted cluster configuration interactions VIE match reasonably well with the experimental spectrum over this wide energy range. Density functional calculations of the corresponding adiabatic terms (AIE) were also performed. Higher energy ionic states were determined by complete active space self-consistent field methods; these include all π-ionizations and some σ-ionic states. These were analyzed by Franck–Condon (FC) procedures and compared with an experiment. The spectral onset is complex, where two states, later shown to be the 12B2 and 12B1 states, are strongly overlapping. The superposition of the FC vibrational structure in the 12B2 and 12B1 states accounts for most of the peaks arising at the onset of the photoelectron spectra. However, the small separation between these two ionic states makes vibronic interaction fairly inevitable. In the absence of Herzberg–Teller analyses for ionic states, we have sought and determined a transition state between the 12B2 and 12B1 states, showing that vibronic coupling does occur. The lack of degradation in the vibrational envelope of the higher of the two states contrasts with our previous work on the halogenobenzenes, where overlapping state envelopes led to considerable widening of the line width at half-height of the higher energy states. [ABSTRACT FROM AUTHOR]

A new vacuum ultraviolet absorption (VUV) spectrum of azulene vapor has been obtained by using a synchrotron radiation source. The onset of the ultraviolet spectrum, previously reported by Sidman et al., has been analyzed in detail by Franck–Condon (FC) and Herzberg–Teller (HT) methods. The photoelectron spectral profile identifies the 3px-Rydberg state 00 band to be 131 cm−1 from the VUV maximum. Excited state energy levels were calculated by three independent methods: the wide scan VUV spectrum was correlated with symmetry adapted cluster configuration interaction calculations. The low energy portion of the spectrum was studied by both time dependent density functional theoretical methods (TDDFT) and multi-reference multi-root CI (MRD-CI). Equilibrium structures were determined for valence states at the TDDFT level. Rydberg states were determined by both TDDFT and MRD-CI. The FC + HT analyses were performed on the TDDFT wave-functions. The HT intensity profiles are generally low in intensity, relative to the FC ones; however, HT is dominant in the second singlet state (S2, 11A1). As a result, numerous non-symmetric modes, their overtones, and combination bands show considerable intensity in that band. Energies obtained from use of extremely diffuse s-, p-, d-, or f-character functions enabled realistic extrapolation to the IE1 for many Rydberg states (RS). The lowest RS (3b13s) based on IE2 lies at 4.804 eV with a quantum defect of 0.714. Differentiation between valence and RS is readily made using the second moments of the charge distribution. [ABSTRACT FROM AUTHOR]

A synchrotron-based photoionization spectrum of azulene shows a significant additional vibrational fine structure when compared to previous studies. This spectrum was successfully analyzed by using Franck–Condon (FC) methods. Previously reported zero-kinetic-energy electron spectra for azulene have been reinterpreted in FC terms, leading to some alternative assignments to the earlier work. The sequence of ionic states has been determined by using ab initio configuration interaction (CI) methods, leading to reliable theoretical values for both the calculated adiabatic ionization energy (AIE) and vertical ionization energy (VIE). VIEs were calculated by both symmetry-adapted cluster (SAC-CI), together with Green's function (GF) and Tamm–Dancoff approximation (TDA), and single excitation CI methods; AIEs for highest states of each symmetry were determined by open-shell self-consistent field (SCF) methods at the restricted Hartree–Fock level. Complete active space SCF was used for the pairs of 12A2 + 22A2 and 12B1 + 22B1 states, each of which occurs as antisymmetric and symmetric (higher energy) combinations. The combined ionic state sequences (AIE and VIE) from these methods are 12A2 < 12B1 < 22A2 < 22B1. The photoelectron spectrum (PES) shows a series of broadbands above 11 eV, each of which is attributed to more than one ionization. The calculated PES sequence of states of up to 19 eV shows that the SAC-CI and GF results are in almost exact agreement. The internal spacing of the bands is best reproduced by the simpler GF and TDA methods. States involving simultaneous ionization and electronic excitation are considered by both SAC-CI and TDA methods. [ABSTRACT FROM AUTHOR]

While thiocarbonyl-stabilised phosphonium ylides generally react upon flash vacuum pyrolysis by the extrusion of Ph3PS to give alkynes in an analogous way to their carbonyl-stabilised analogues, two examples with a hydrogen atom on the ylidic carbon are found to undergo a quite different process. The net transfer of a phenyl group from P to S gives (Z)-configured 1-diphenylphosphino-2-(phenylsulfenyl)alkenes in a novel isomerisation process via intermediate λ5-1,2-thiaphosphetes. These prove to be versatile hemilabile ligands with a total of seven complexes prepared involving five different transition metals. Four of these are characterised by X-ray diffraction with two involving the bidentate ligand forming a five-membered ring metallacycle and two with the ligand coordinating to the metal only through phosphorus. [ABSTRACT FROM AUTHOR]

A synchrotron-based vacuum ultraviolet (VUV) absorption spectrum of norbornadiene (NBD) is reported, and the extensive vibrational structure obtained has been analyzed. The previously known 5b13s-Rydberg state has been reinterpreted by comparison with our recent high-resolution photoelectron spectral analysis of the X2B1 ionic state. Additional vibrational details in the region of this Rydberg state are observed in its VUV spectrum when compared with the photoelectron 2B1 ionic state; this is attributed to the underlying valence state structure in the VUV. Valence and Rydberg state energies have been obtained by configuration interaction and time-dependent density functional theoretical methods. Several low-lying singlet valence states, especially those that arise from ππ* excitations, conventionally termed NV1 to NV4, have been examined in detail. Their Franck–Condon (FC) and Herzberg–Teller (HT) profiles have been investigated and fitted to the VUV spectrum. Estimates of the experimental 00 band positions have been made from these fits. The anomaly of the observed UV absorption by the 1A2 state of NBD is attributed to HT effects. Generally, the HT components are less than 10% of the FC terms. The calculated 5b13s lowest Rydberg state also shows a low level of HT components. The observed electron impact spectra of NBD have been analyzed in detail in terms of triplet states. [ABSTRACT FROM AUTHOR]

The X-ray structure of the title compound, formed at low conversion in the reaction of thiosalicylic acid with thionyl chloride, has been determined. The acid chloride groups are oriented to permit an attractive non-bonding O...S interaction. Mechanisms are suggested for the formation of this unexpected product. 1H and 13C NMR data are also reported for the first time for the major reaction product, 2-mercaptobenzoyl chloride. [ABSTRACT FROM AUTHOR]

The title dibromodisalicylaldehyde, obtained as a by-product in the m-chloroperoxybenzoic acid oxidation of 5-bromo-2-(methoxymethoxy)benzaldehyde, has been characterised by IR and NMR spectroscopy and X-ray diffraction. The structure features two independent molecules with a π–π stacking interaction between them. [ABSTRACT FROM AUTHOR]

The product formed by base-induced dimerisation of (2S,5S)-2-tert-butyl-5-methyl-1,3-dioxolan-4-one is shown by X-ray diffraction to be the title compound and not the isomeric fused-ring 1,3-dioxolane/1,3-dioxane-4-one structure proposed by previous researchers. The analogous compound derived from (2S,5S)-5-benzyl-2-tert-butyl-1,3-dioxolan-4-one has also been obtained and characterised. [ABSTRACT FROM AUTHOR]