The Photoelectron Spectra of 4, 13-Diaza- and 4, 16-Diaza [24] (1,2,4,5)cyclophanes

A tentative assignment is proposed for the He (Ia) photoelectron (PE.) spectra of the title compounds. It is based on the assumption that the first four π-bands occupy the same position in both spectra, as suggested by a qualitative correlation with the PE. spectrum of [2₄](1,2,4,5)cyclophane and by a previously proposed molecular orbital model. If this is accepted, then the bands due to electron ejection from the lone-pair orbitals are split by roughly 0.8 eV in the case of the 4, 13-diaza isomer, whereas no split can be detected in the case of the 4, 16-diaza isomer.     

Photoelectron Spectra of Azabenzenes and Azanaphthalenes: I. Pyridine,diazines, s-triazine and s-tetrazine

The experimental and theoretical basis of a recently proposed reassignment of the bands in the PE. spectra of pyridine, pyridazine, pyrimidine and pyrazine is discussed in detail. A characteristic feature of the derived orbital sequence is that it takes the ‘through-space’ and ‘through-bond’ interaction between the ‘lone pair’ basis orbitals explicitly into account. A simple parametrization of the orbital energies, based on HMO-type models for the π-orbitals and for the ‘lone pair’ linear combinations, yields excellent agreement with the observed band positions in the PE. spectra of s-triazine and s-tetrazine. Our new assignment is compared to those proposed previously.     

Collision-energy-resolved Penning ionization electron spectroscopy of bromomethanes (CH3Br, CH2Br2, and CHBr3) by collision with He*(2(3)S) metastable atoms

Ionization of bromomethanes (CH3Br, CH2Br2, and CHBr3) upon collision with metastable He*(2(3)S) atoms has been studied by means of collision-energy-resolved Penning ionization electron spectroscopy. Lone-pair (nBr) orbitals of Br4p characters have larger ionization cross sections than sigma(C-Br) orbitals. The collision-energy dependence of the partial ionization cross sections shows that the interaction potential between the molecule and the He*(2(3)S) atom is highly anisotropic around CH3Br or CH2Br2, while isotropic attractive interactions are found for CHBr3. Bands observed at electron energies of approximately 2 eV in the He*(2(3)S) Penning ionization electron spectra (PIES) of CH2Br2 and CHBr3 have no counterpart in ultraviolet (He I) photoionization spectra and theoretical (third-order algebraic diagrammatic construction) one-electron and shake-up ionization spectra. Energy analysis of the processes involved demonstrates that these bands and further bands overlapping with sigma(C-Br) or piCH2 levels are related to autoionization of dissociating (He+ - Br-) pairs. Similarly, a band at an electron energy of approximately 1 eV in the He*(2(3)S) PIES spectra of CH3Br has been ascribed to autoionizing Br** atoms released by dissociation of (unidentified) excited states of the target molecule. A further autoionization (S) band can be discerned at approximately 1 eV below the lone-pair nBr bands in the He*(2(3)S) PIES spectrum of CHBr3. This band has been ascribed to the decay of autoionizing Rydberg states of the target molecule (M**) into vibrationally excited states of the molecular ion. It was found that for this transition, the interaction potential that prevails in the entrance channel is merely attractive.     

Probing weak molecular orbital interactions in non-conjugated diene molecules by means of near-edge X-ray absorption spectroscopy

Carbon and oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra of 1,4-cyclohexadiene, p-benzoquinone, norbornadiene, norbornadienone, and cis-cis-[4,4,2]propella-3,8-diene-11,12-dione were calculated by means of Hartree-Fock and hybrid density functional theory using the static-exchange (STEX) approximation. The NEXAFS spectra are used as a probe to identify weak molecular interactions between the two non-conjugated ethylenic pi* orbitals present in these molecules. We show that the X-ray absorption spectrum of 1,4-cyclohexadiene exhibits some particular spectral structures in the discrete energy region that evidence diene through-bond orbital interaction, whereas absorption peaks are identified in the norbornadiene and norbornadienone spectra that indicate effective through-space orbital interactions. The molecular structure of the cis-cis-[4,4,2]propella-3,8-diene-11,12-dione isomer is such that the indirect through-bond or through-space diene orbital interactions are too weak to be assigned by its C1s NEXAFS spectrum.     

Inverted Hyperconjugation in Symmetrical 1,4-Dihalocubanes

The σ-orbital manifold of cubane 1 , as suggested by its PE spectrum, is divided into two sets separated by a 3 eV gap extending from ～ -10.5 eV to ～ -13.5 eV. Halogen substituents with np AO basis energies falling into this gap (e.g. Cl or Br) will, therefore, hyperconjugate appreciably with both sets. Interaction with the lower-lying set will lead to the usual destabilization (‘normal’ hyperconjugation), whereas interaction with the set above will necessarily lead to a ‘stabilization’ (‘inverted’ hyperconjugation). As a result the lone-pair ionization energies of Cl or Br substituted cubanes (derived from PE spectra) are much larger than naively expected for an alkyl halide containing as much as 8 C-atoms. In particular no significant shift of the e lone-pair bands in the PE spectra of 1,4-dichloro- and 1,4-dibromocubane can be detected with respect to the first ionization energies of the free atoms Cl and Br, or of HCl and HBr.     

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—I : Lone-pair orbital interactions in cis- and trans-hydrazines

Ab initio SCF MO calculations using STO-3G basis set were performed on the cis- and trans- hydrazines. The cannonical MOs obtained by these calculations were then transformed into the localized MOs. With the use of the localized MOs thus obtained, the variation in the lone-pair orbital energies of the molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized MOs. As a result of this analysis, it was found that ; (a) the effect of the inner shell orbitais, l s electrons of N atoms, is not negligibly small, (b) the effect of the through-bond interaction is not so larger than the through-space interaction, and (c) the large contribution of the through-space interaction is caused from the indirect as well as direct interactions between two lone-pairs.     

Lone-pair orbital interactions in polythiaadamantanes

The electronic structures of a series of polythiaadamantanes from thiaadamantane through 2,4,6,8,9,10-hexathiaadamantane (HTA) have been analyzed using density functional theory calculations in conjunction with Hückel and natural bond orbital analysis. The effects of multiple sulfur p-type lone-pair orbital interactions on ionization potentials, hole mobilities, and electronic coupling have been determined. An overall increase in the average energy of the lone-pair orbitals as the number of sulfur atoms increases is predicted, with the exact positioning of the HOMO depending on specific lone-pair interactions. Separation of through-bond (TB) and through-space (TS) interactions between intramolecular sulfur atoms has been performed using localized molecular orbitals and model systems based on interacting hydrogen sulfide molecules. TB interations were found to reduce orbital splitting, while TS interactions were found to increase orbital splitting. TS interactions were more or less constant from one polythiaadamantane to the next, and the contributions of TB effects to individual orbital energies vary depending on the relative orientation of sulfur atoms as determined by the sigma molecular framework. Electronic coupling between intermolecular sulfur lone-pair orbitals was determined by investigating unique dimer pairs observed in the crystal structure of HTA. Electronic coupling is not as strong as expected given the short intermolecular S-S distances observed in the crystal structure. In general, B3LYP/6-31G(d) and B3LYP/6-311+G(d,p) give very similar orbital energies and splittings.     

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—II : Lone-pair orbital energies in bicyclo compounds: 7-azabicyclo[2.2.1]heptane and 2-azabicyclo[2.2.2]octane,and their n-methyl derivatives

Ab intio SCF MO calculations using STO-3G basis set were performed on 7-azabicyclo[2.2.1]heptane, N-methyl-7-azabicyclo[2.2.1]heptane, 2-azabicyclo[2.2.2)octane, N-methyl-2-azabicyclo[2.2.2)octane, and their model molecules. The orbital energies obtained by these calculations were compared with the experimental ionization potentials The canonical MOs obtained for the model molecules were then transformed into the localized Mos. With the use of the localized MOs thus obtained, the lone-pair orbital energies were pursued in the light of the through-space and/or the through-bond interactions between thw specified localized MOs. As a result of this analysis, it was found that the effects of the inner shell orbitals, 1s electrons of the N atom, and of the neighbouring N-C bonds of the skeleton (through-bond interaction) play a dominant role in the interaction with the lone-pair orbitals. It was also found that the effect of the N-Me group on the lone-pair orbital energy is considerably important.     

Chalkogenfluoride in niedrigen Oxydationsstufen. X Thermochemische Daten und Photoionisations-Massenspektren von SSF2, FSSF,SF3SF und SF3SSF

Lower Chalcogen Fluorides. X. Thermochemical Data and Photoionization Mass Spectra of SSF₂, FSSF, SF₃SF, and SF₃SSF From measurements of the equilibrium of the system SSF₂ ? FSSF a reaction enthalpy ?H = 11.3 ± 1.5 kJ/mol is evaluated. Enthalpies of formation and bond energies of SSF₂, FSSF, SF₃SF, and SF₃SSF have been obtained from appearence potentials which have been measured by photoionization mass spectrometry.     

B(OCH3)3电子结构的Hel紫外光电子能谱研究

人们知道，Hel紫外光电子能借（PES）提供研究分子轨道能量、能级次序、成键类型以及由光电子峰强度所反映的电离轨道特性等信息是其他手段没有的，因而PES技术已广泛地用于众多化合物分子电子结构的研究中．有机础化合物由于它们高的反应活性作为合成试剂而信受人们重视［‘－     

VUV and photoelectronic spectra of methylstannane. Theoretical and experimental approach

The vacuum ultraviolet (VUV) and photoelectron spectra of SnH₃CH₃ were recorded between 6.20 and 11.28 eV and between 8 and 17 eV, respectively. Spectra were interpreted using ab initio CI calculations. The photoelectron spectrum confirmed the low SnC bond energy. The first two ionization potentials (IP) observed were attributed to the ionization of the a₁ (10.65 eV) and e orbitals (11.15 and 11.60 eV, split by the Jahn-Teller effect), thereby showing an inversion of IPs compared with ethane. Similarly, the first two bands of the VUV spectrum (at 7.04 and 7.72–8.16 eV) were attributed to a₁ and e transitions towards the Rydberg s orbital. A splitting of the same order of magnitude as that of the photoelectron spectrum could be noted in the E state. Observed transitions between 8.65 and 10 eV showed a strong interaction between the Rydberg p MO and the σ^*_SnC antibonding orbital. Primarilyvalence transitions were encountered beyond 10 eV.     

XPS study of one-dimensional compounds: TiS3

X-Ray photoelectron spectra of TiS₃ with a one-dimensional structure were measured. TiS₃ may be regarded as Ti⁴⁺(S₂)^2?S^2? with pairs of S atoms (S₂) and isolated S atoms. The spectra of the sulfur core-levels are assigned by comparison with those of TiS₂, where all S atoms are largely separated. The binding energy of the S₂ pairs is found to be 1.4 eV higher than that of the isolated S atoms, which is consistent with the larger negative charge of the isolated atoms. The structures of the valence band of TiS₃ are discussed in terms of a molecular orbital scheme for the S₂ pairs.     

Photoelectron-spectroscopic Evidence Concerning “Homo-aromaticity”

The first of the two π-bands in the photoelectron spectrum of cis-cis-cis-1, 4, 7-cyclononatriene (I, symmetry C_3v) shows a Jahn-Teller split. This is consistent with the prediction of molecular orbital theory that the top occupied orbitals of I are e (π) and a ₁(π) respectively. From the difference ?( e (π)) - ?( a ₁(π)) = 0.90 to 0.97 eV a value of β_1,3 = ?0.68 eV = 0.27 β (β = -2.5 eV) is obtained for the homoconjugative interaction of two π-orbitals in I. This value represents almost exclusively through-space interaction between the π-orbitals. Through-bond interaction (hyperconjugation) is a minor effect in I. A comparison of the photoelectron data of bicyclo [4.2.1] nonatriene with those of norbornene and cycloheptadiene shows that homoconjugation (homo-aromaticity) can only be detected by photoelectron spectroscopy if the interacting π-bonds (basis orbitals) are symmetry equivalent or have accidentally (almost) degenerate energies.     

The Interaction of π-Orbitals in Barrelene

The photoelectron spectrum (PE. spectrum) of barrelene (bicyclo[2.2.2]octatriene, 4 ) is recorded and the first four bands are correlated with orbitals obtained with the MINDO/2-SCF procedure. The structural changes accompagnying the ionisation process 4 → 4 ⁺ are qualitatively derived from the features of the top-occupied a′₂ (π) MO of 4 , which shows complete σ-π separation. The vibrational pattern of the corresponding PE. band 1. as well as complete energy-minimisation of the geometries of 4 and 4 ⁺ support the conclusion that 4 is a rather strained molecule. The interaction of the three π? bonds in 4 are discussed in terms of ‘through-space’ and ‘through-bond’ interaction with lower lying σ-orbitals. It is found that the latter is far from being negligible.     

Interactions between Oxygen Lone-Pair Orbitals and Double-Bond π-Orbitals in β,γ-Unsaturated,Bicyclic Ketones; a PE-Spectroscopic Investigation

The HE(Iα) photoelectron (PE) spectra of 2,3,5,6-tetramethylidene-2-bicyclo[2.2.1]heptanone ( 12 ), 5,6-dimethylidene-2-bicyclo[2.2.1]heptanone ( 14 ), 5,6-dimethylidene-2-bicyclo[2.2.2]octanone ( 16 ), and 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone ( 17 ) have been recorded, Comparison with the PE data of other β,γ-unsaturated ketones and parent alkenes, and with the result of ab initio STO-3G calculations, confirm the existence of significant interactions between the oxygen lone-pair orbital n_o and the double-bond π orbital(s). It is argued that the major contributions to the basis energy shifts and to the cross term between the n_o and π orbitals are due to a ‘through-bond’ mechanism.     

The gas-phase conformation of 3,7-dimethyl-3,7-diazabicyclo[3.3.1]nonane

The gas-phase conformation of the title compound (1) is discussed in reference to its photoelectron spectrum. The experimental lone-pair/lone-pair splitting (0.51 eV), when compared with that of similar diamines and with the results of three sets of MO calculations (MINDO/3, MNDO and STO-3G), leads to the conclusion that 1 exists in the chair-chair conformation. A remarkable sensitivity of the calculations to slight changes in the geometry is noted, and it is suggested that calculations of this type must include geometry-optimization. The question of through-space vs through-bond inteaction of the nitrogen lone pairs was explored by performing MNDO calculations in which the N-N resonance integrals were set to zero. These calculations indicate that in the chair-chair conformation the N-N interaction is mainly through-space. The ¹³CNMR and Ni(acac)₂-induced ¹³C shifts of 1 are discussed.     

Untersuchung von Schwefel-Fluor-Verbindungen durch Codestillation und Cosublimation im Cady-Rohr

Zusammenfassung Das Trennverfahren der quantitativen Codestillation und Cosublimation ist zur Untersuchung von Schwefel-Fluor-Verbindungen eingesetzt worden, die vorwiegend Schwefel in niedriger Oxidationsstufe enthalten. Die neue Technik, die sich ideal für die Analyse luftempfindlicher und korrosiver Gasmischungen eignet, ermöglichte die Trennung kleiner Stoffmengen von SOF₂, SSF₂, FSSF und SF₃SF durch Destillation und die Charakterisierung dieser Stoffe durch ihre Dampfdrücke sowie die sich daraus ergebenden thennodynamischen Daten der Verdampfung bei sehr niedrigen Drücken. Mischungen aus SF₃SF und FSSF sowie FSSF und SSF₂ verhalten sich beim Sieden ideal, SSF₂ und SF₄ bilden ein azeotropes Gemisch mit SF₄ im Überschuß. SF₆ kann von den weniger flüchtigen Schwefelfluoriden durch Cosublimation leicht abgetrennt werden und als Standard für die Bestimmung von Stoffmengen und molaren Massen durch Verflüchtigung im Stickstoff- und Argonstrom dienen.Die Auswertung der Daten, die bei der Sublimation des Trifluorosulfoniumtetrafluoroborates, SF ₃ ⁺ BF ₄ ^– im Cady-Rohr erhalten wurden, bewiesen, daß die Flüchtigkeit dieser Verbindung auf ihre Dissoziation in SF₄ und BF₃ zurückzuführen ist.

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Investigation of sulfur fluorine compounds by codistillation and cosublimation in the Cady tube

Summary The separation concept of quantitative codistillation and cosublimation has been used to investigate sulfur fluorine compounds with sulfur in a lower oxidation state. The new technique, which is ideally suited to analyse air sensitive and corrosive gas mixtures, enabled the separation of small quantities of SOF₂, SF₄, SSF₂, FSSF and SF₃SF by distillation, and to characterize these compounds through their vapour pressures and thermodynamic data of vaporization at low pressures. Mixtures of FSSF and SF₃SF, and, FSSF and SSF₂ behave ideally on boiling, whereas SSF₂ and SF₄ form an azeotropic system with SF₄ in excess. SF₆ can easiliy be separated from the less volatile sulfur fluorides by cosublimation and may be used as a standard for the estimation of the amount of substances and molar masses through volatilization in nitrogen and argon. The evaluation of data obtained through the sublimation of trifluorsulfonium tetrafluoroborate in the Cady tube proved that the votalization process is caused by the dissociation of SF ₃ ⁺ BF ₄ ^– to yield SF₄ and BF₃.

     

The electronics structures of small strained rings. An investigation of the interaction between the oxygen and the π orbitals in 3-methyleneoxetane and 3-oxetanone

The ultraviolet photoelectron spectra of 3-methyleneoxetane (I), 3-oxetanone (II) and β-propiol-octane (III) have been investigated for the purpose of studying the interaction processes between the endocyclic oxygen and the methylene or carbonyl groups of I and II, respectively. Molecular orbital calculations at the MINDO/3, MNDO, and STO-3G/431-G levels have been performed to aid analyses of the data. The interaction process occurs primarily through the pseudo-π-CH₂ orbitals for I and II. Substantial stabilizing inductive effects are noted for the lone-pair and π orbitals for these molecules.     

A quantitative analysis of the through-space and the through-bond interactions between lone-pairs in azines: pyridazine,pyrimidine and pyrazine

The INDO calculations were performed on the three azines: pyridazine, pyrimidine, and pyrazine. The cannonical molecular orbitais obtained by these calculations were then transformed into the localized molecular orbitals. With the use of the localized molecular orbitals, the variation in the lone-pair orbital energies of these molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized molecular orbitals in a molecule selectively. The interactions were expressed by the summation of several terms: through-space, through-bond, through-virtuals and coupling terms.     

A Quantitative Assessment of „Through-space”︁ and „Through-bond”︁ Interactions. Application to Semi-empirical SCF Models

The scheme of ‘through-space’ and ‘through-bond’ interaction of (semi)localized orbitals, originally proposed by Hoffmann, is reexamined in terms of SCF many-electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off-diagonal matrix elements of the Hartree-Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalized Hartree-Fock matrices referring to ‘precanonical orbitals’. The procedure outlined is applied to three practical examples using the semiempirical many-electron treatments SPINDO, MINDO/2 and CNDO/2:

• a A reassessment of ‘through-space’ and ‘through-bond’ interaction in norbornadiene indicates, that the latter type of interaction is also of importance for the orbital based mainly on the antisymmetric combination of the localized x-orbitals. The differences in the predictions derived from the three models are critically examined.
• b The competition between ‘through-space’ and ‘through-bond’ interaction in the series of bicyclic dienes from norbornadiene to bicyclo[4.2.2]-dcca-7,9-diene and in cyclohexa-1,4-diene, i. e. their dependence on the dihedral angle UI is reexamined. It is found that the rationalization for the orbital crossing near ω = 130° deduccd from PE. spectroscopic data can not be as simple as originally suggested and that the relay’ orbitals responsible for ‘through-bond interaction affecting both the symmetric and the antisymmetric combination of the π-orbitals extend over the whole CC-σ-system of the six membered ring.
• c ‘Through-bond’ interaction of the two lone pair orbitals in 1,4-diazabicyclo[2.2.2]octane is found to be large for their symmetric and the antisymmetric linear combination.

The analysis quoted, draws attention to some of the dangers involved in using semiempirical treatments for the interpretation of PE. data in terms of Koopmans′ theorem, without due caution.