Structural chemistry of polycyclic heteroaromatic compounds. Part XI. Photoelectron spectra and electronic structures of tetracyclic hetarenes of the triphenylene type

The UV photoelectron spectra of several tetracyclic heteroaromatic compounds (2-9) which are pi-isoelectronic with triphenylene (1) have been recorded and analysed making use of semiempirical AM1 and PM3 as well as ab initio/DFT B3LYP calculations. In one series of compounds (2-7), the peripheral benzene rings of 1 are successively substituted by thiophene rings that are either [b]- or [c]-annellated with the central benzene unit. In 2-7 only marginal shifts are found for most of the IPs of electrons. In the benzotrithiophenes 5-7, a systematic variation is displayed by IP(pi7). Compared to 1, the pi electron system of benzo[c]trithiophene (7) is approximately two times as much destabilized as in the isomers 5 and 6 with [b]annellated thiophene rings. The IP[n(S)] values of the thiophene derivatives 2-7 indicate that these orbitals are clearly destabilized relative to thiophene. The same holds for the n(O) orbital of the furane derivative 9 in comparison with that of furane. In 9, only the higher pi MOs (pi7-pi9) are destabilized whereas the lower levels (pi1-pi4) are stabilized, and those in between (pi5-pi6) remain essentially unshifted. In the pyrrole derivative 8, all pi MOs are substantially destabilized by about 0.5-1.6 eV relative to 1.     

Quadricyclanes. Part I: Photoelectron spectra and electronic structure

The photoelectron spectra of quadricyclane ( 3 ) and 3-methylidene quadricyclane ( 4 ) have been measured. The results served as a basis for the elucidation of the electronic structure of these compounds, which agreed with theoretical calculations. It is found that the symmetry of the HOMO of 3 is different when compared to that of its valence isomer norbornadiene ( 1 ). The results also indicate that the structure of the highest occupied orbitals cannot be derived by only considering the Walsh-orbitals of the two three-membered rings. In addition one of the Walsh-components of the four-memebered ring has to be taken into account.     

Photoelectron spectra and electronic structures of some chlorosulfonyl pseudohalides

The electronic structures of chlorosulfonyl pseudohalide ClSO2X (X = Cl, NCO, N3) are studied by photoelectron spectroscopy (PES) combined with the OVGF calculation at 6-311++G(3df) basis sets. The first ionization potentials for ClSO2NCO and ClSO2N3 are determined to be 12.02 and 11.43 eV, respectively, for the first time, and their features in the PE spectra were assigned based on comparison with related compounds and with high level quantum calculations. Photoelectron spectra of ClSO2NCO and ClSO2N3 suggest that the interactions between chlorine "lone-pair" electrons and two pseudohalogen groups have significant effect on the HOMOs of two compounds, besides the influence of their electronegativity on the first ionization energies.     

1H and13C NMR spectra of polycyclic compounds

Using 2D¹H and¹³C correlation NMR spectroscopy, all signals in the¹H and¹³C NMR spectra of five stereoisomeric bicyclo[2.2.1]heptadiene trimers, decacyclo[9.9.1.0^2.10.0^3.8.0^4.6.0^5.9.0^12.20.0^13.18.0^14.16.0^15.19]heneicosanes, obtained by Pd-catalyzed codimerization of norbornadiene dimer with quadricyclane followed by homocyclotrimerization of the latter were assigned unambiguously. Independent stereochemical identification of the trimers was performed using data on the nuclear Overhauser effect.     

Photoelectron spectra and ion chemistry of imidazolide

The 351.1 nm photoelectron spectrum of imidazolide anion has been measured. The electron affinity (EA) of the imidazolyl radical is determined to be 2.613 +/- 0.006 eV. Vibrational frequencies of 955 +/- 15 and 1365 +/- 20 cm(-1) are observed in the spectrum of the (2)B1 ground state of the imidazolyl radical. The main features in the spectrum are well-reproduced by Franck-Condon simulation based on the optimized geometries and the normal modes obtained at the B3LYP/6-311++G(d,p) level of density functional theory. The two vibrational frequencies are assigned to totally symmetric modes with C-C and N-C stretching motions. Overtone peaks of an in-plane nontotally symmetric mode are observed in the spectrum and attributed to Fermi resonance. Also observed is the photoelectron spectrum of the anion formed by deprotonation of imidazole at the C5 position. The EA of the corresponding radical, 5-imidazolyl, is 1.992 +/- 0.010 eV. The gas phase acidity of imidazole has been determined using a flowing afterglow-selected ion tube; delta(acid)G298 = 342.6 +/- 0.4 and delta(acid)H298 = 349.7 +/- 0.5 kcal mol(-1). From the EA of imidazolyl radical and gas phase acidity of imidazole, the bond dissociation energy for the N-H bond in imidazole is determined to be 95.1 +/- 0.5 kcal mol(-1). These thermodynamic parameters for imidazole and imidazolyl radical are compared with those for pyrrole and pyrrolyl radical, and the effects of the additional N atom in the five-membered ring are discussed.     

The sulfonation of aromatic and heteroaromatic polycyclic compounds

Relative reactivities of a series of polycyclic carbo- and heteroaromatic compounds to sulfonation by sulfur trioxide in nitrobenzene are measured and discussed. The results show the following reactivity in decreasing order: indole, carbazole, pyrene, perylene, naphthalene, phenanthrene, benzene, benzothiophene, and dibenzothiophene.     

13C NMR spectra of polycyclic compounds. Bicyclo[2.2.1]heptadiene tetramers

Comparison of experimental and calculated chemical shifts of carbon atoms in¹³C NMR spectra of two isomeric dodecacyclo[14.9.1.1^4,13.1^7,10.0^2,15.0^3,14.0^5,12.0^6,11.0^17,25.0^18,24.0^19,21. 0^20,24]-octacos-8-enes, bicyclo[2.2.1]heptadiene tetramers, confirmed theirexo-trans-exo-trans-exo-endo-andexo-trans-exo-trans-exo-exo-configurations. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2545–2547, December, 1998.     

Photoelectron spectra and electronic structure of aza-boron-dipyridomethene derivatives

The electronic structure of three aza-boron-dipyridomethene derivatives containing different hydrocarbon groups at the boron atom is studied by ultraviolet photoelectron spectroscopy and calculations at the density functional theory level. According to the experimental and theoretical data, the higher occupied molecular orbitals of anthracene, acridine, and the studied complexes are of the same character. For the three studied compounds, the effect of alkyl and phenyl substituents on the electronic structure is determined. The parameters of the electronic structure of aza-boron-dipyridomethene (phenyl groups at the boron atom) and its β-diketonate analogue are compared. It is shown that in an energy range up to 11 eV the calculated results correlate with the ultraviolet photoelectron spectra.     

13C NMR spectra of polycyclic compounds and the stereochemistry of norbornadiene dimers and trimers

Conclusions We have obtained the¹³C NMR spectra of all known dimers and trimers of norbornadiene. We have determined the principles governing the changes in chemical shifts depending on the orientation interactions of the fragments and carried out the stereochemical assignment of all known isomers. We have shown the agreement of the configurations of the latter determined by the¹³C NMR method with their structures previously established by other methods.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2492–2497, November, 1984.     

Photoelectron spectra,electronic and spatial structure of phenylhydrazones

Theoretical and Experimental Chemistry -     

Photoelectron spectra and electronic structure of derivatives of imidazoline

We have obtained for the first time the photoelectron spectra (PES) of 20 diamagnetic and paramagnetic derivatives of imidazole. On the basis of calculations in the MNDO approximation, analysis of the vibrational structure, and comparisons in a series we have interpreted the bands in the range 7–11 eV. In the nitroxyl radicals of 3-imidazoline the highest occupied molecular orbital is the _NO ^* orbital, having also a contribution on the C⁴ atom. On introducing N-oxide groups there is a considerable rearrangement of the electronic structure of the radicals. In the PES of the nitroxyl radicals of 3-imidazoline-3-oxide there is multiplet splitting of the ionization band of the n_o·MO, amounting to 0.3–0.4 eV. Replacement of the methyl groups on the C² atom by methoxyl groups leads to an increase in the interactions of the unshared pairs of the O atoms of the nitronium and nitroxyl groups, while the same replacement on the C⁵ atoms leads to a considerable decrease in this interaction. When the substituent on the N¹ atom in derivatives of 3-imidazoline-3-oxide is varied the energy of ionization of the _C-NO MO decreases in the series: CH₃ < H OH < O < NO.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1769–1777, August, 1990.     

Photoelectron spectra and electronic structure of nitrogen-containing chelate boron complexes

A brief review of the results of studying some classes of nitrogen-containing chelate boron complexes by ultraviolet photoelectron spectroscopy and density functional theory is reported. The quantum chemical modeling of the substitution effects of a complexing agent, heteroatoms, and functional groups in α, β, and γ positions of the chelate ring allowed us to establish the features of the electronic structure of the studied complexes. It is found that the substitution of heteroatoms in the chelate ring has no substantial influence on the structure of the highest occupied molecular orbital (HOMO). In imidoylamidinate complexes, as opposed to formazanates and β-diketonates, there is no noticeable mixing of π orbitals of the chelate and benzene rings. In condensed nitrogen heterocycles the HOMO is stabilized by 0.2-0.3 eV and π orbitals of the benzene ring are stabilized by 0.8-1.2 eV. The HOMO of substituted aza-boron-dipyridomethene correlates with anthracene and acridine π₇ orbitals, which causes the fine structure of the first band. It is shown that in an energy range below 11 eV the calculated results reproduce well the energy gaps between the ionization states of the complexes.     

Photoelectron spectra and electronic structure of VF5 and VOF3

Using the gas-phase photoelectron spectroscopy and SCF-X-SW methods, we have studied the electronic structure of fluorides of five-valent vanadium VF₅ and VOF₃. The values of the ionization potential calculated in the transition state approximation agree well with the experimental values. The V-F covalent bonding is accomplished by the ie, 2e, 3a₁ electrons in the pentafluoride and the 3e, 2e, 3a₁ electrons in VOF₃. The short V=O bond is realized by the 3a₁ and 5a₁ electrons and the 5e electrons. We show that the shortening of the VO bond compared with the VF bond is also due to the higher effective charge on the oxygen.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol., No. 3, pp. 348–353, May–June 1988.The authors thank É. G. Rakov and A. S. Dudin for providing the vanadium compounds, and V. A. Andreev for helping with the calculation for VF₅.     

Photoelectron spectra and electronic structure of some 4-substituted 2-allylanisoles

The electronic structures of 4-substituted 2-allyl anisoles (1-9) have been investigated by ultraviolet photoelectron spectroscopy and quantum chemical methods. The ionisation potentials corresponding to the pi MOs pi(2) and pi(3) of the phenyl ring, and the n(O) orbital of the methoxy group as well as the allylic pi(C=C) orbital could be determined and assigned for 1-9. Linear regression analyses of the IPs related to these orbitals with different substituent constants indicated that Hammett sigma(p) values performed satisfactorily to fair for pi(2), pi(3) and n(O) but poor for allylic pi(C=C). Other substituent constants such as R and R(-) were fair only for pi(2) and pi(3), but poor for n(O) and pi(C=C).     

13C-NMR spectra of polycyclic compounds and the stereochemistry of unsaturated derivatives of bicyclo[2.2.1]hept(en)ane and related structures

Conclusions Structures of a series of unsaturated bicyclo[2.2.1]hept(en)ane derivatives and related compounds have been established by analysis of their¹³C-NMR spectra, which has also permitted stereochemical assignments of cyclopropane, cyclobutane, and cyclopentene fragments and vinyl groups, relative to the norbornane backbone in each molecule. In the case of 7,7-spirocyclopropane derivatives of norbornane and norbornene, the chemical shift difference for the methylene groups of the cyclopropane fragment proved to be stereochemically informative.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1018–1024, May,1987.     

Photoelectron spectra of group V compounds. The elements: Sb4

The high-temperature He I photoelectron (PE) spectrum of gaseous Sb₄ is presented and assigned on the basis of the known PE ionisation energies of As₄ and P₄ and from SCC Xa eigenvalues and eigenvectors. Implications for the PE spectra of related antimony compounds are discussed.