József Réffy

Investigation of heterocyclic compounds containing a PC or AsC bond by ultraviolet photoelectron spectroscopy

Abstract The He(I) ultraviolet photoelectron spectra of benzene-fused heterocycles containing AsC and PC double bond have been recorded, and interpret MNDO and CNDO/S quantum-chemical calculation carried out to assist interpretation of the data. The analysis of the spectra indicates that there is a strong interaction between the EC double bond and the π-system of the molecule. In contrast the conjugative effect of the phosphorous or arsenic lone pair gives rise to completely different spectra for 1,3-benzazaphospholes or -arsoles substituted in 1 or 3 positions.

Density functional study of the equilibrium geometry and Si-O-Si potential energy curve of disiloxane

Abstract Calculations of the barrier to linearization of disiloxane using various methods (HF, MP2, CCSD(T) and DFT) with doublezeta and triple-zeta basis sets plus a single d-set yield very low or no barrier. The CCSD(T) results calculated with triple-zeta basis sets plus a single d-set is in agreement with recent experimental results (0.30 kcal mol ). However, the same methods produce a higher barrier (≈ 1.4 kcal mol ) using a more expanded basis set. The results calculated with various density functional methods show a similar basis set dependence. The inclusion of the f functions into the basis lowers the barrier. The barrier calculated using the combination of Becke and Perdew (B-P86) functionals is in good agreement with coupled cluster results. The coefficients of a polynomial interpolation for the correlation energy as a function of the Si-O-Si bond angle are also given.

Structure of disiloxane: a semiempirical and Post-Hartree—Fock study

The semiempirical (MNDO, AM1, and PM3) and ab initio predicted structure of disiloxane is studied with a series of basis sets and inclusion of electron correlation at MP2, MP3, MP4, CCD, CCSD, and CCSD(T) levels. The calculated molecular geometry and barrier to linearization of the SiOSi bond angle are compared with previous theoretical and experimental values. Our results show that the calculated barrier to linearization is very sensitive to the number of polarization functions in the basis set. We also investigate the coupling between the SiOSi bond angle and the SiO bond length and calculate the Mulliken and electrostatic potential‐derived charges. For comparison purposes we also calculate the molecular geometry, the barrier to linearization of the SiOSi bond angle, and the atomic charges in hexamethyldisiloxane.

The Photoelectron Spectrum and Conformation of Phenylphosphine and Phenylarsine

He(I) and He(II) photoelectron spectra of phenylphosphine and phenylarsine have been investigated and assigned. The rotational barrier of the phosphino group has been investigated at the MP2/6-31G(d,p)//MP2/6-31G(d,p) and HF/6-31G(d,p)//HF/6-31G(d,p) levels of theory, and that of the arsino group at the HF/6-31G(d,p)//6-31G(d,p) levels of theory. The rotational barrier of the two molecules is nearly the same. The energy difference between the two possible conformers of the molecules is low (1.5 kJ/mol at the MP2/6-31G(d,p) level of theory), allowing nearly free rotation about the P-C bond. The photoelectron spectrum cannot be interpreted by considering the most stable rotamer, but all possible conformers should be taken into account. The present interpretation is consistent with the smallnp- π interaction concluded from other investigations. The rotational barrier ofo-phosphinophenol is significantly larger than for phenylphosphine, and the photoelectron spectrum of this compound can be interpreted by considering a single conformer, and no appreciable interaction between the π-system of the ring and the phosphorus lone pair.

Investigation of 3-substituted benzazaphospholes and benzazarsoles by UV-photoelectron spectroscopy

Abstract The conjugative interaction in some phosphorus and arsenic analogues of benzimidazoles has been studied by UV photoelectron spectroscopy. The spectra have been interpreted with the aid of MNDO quantum-chemical calculations and comparison with other compounds containing trivalent P or As atoms. Comparison of the band positions for the P lone pair in various compounds indicated that the interaction with the π-system is small, and it is even lower for the arsenic lone pair.

Photoelectron spectrum and reactivity of silylalkyl sulphides. Stabilization of radical cations by the β-silyl effect

Abstract The effect of a β-silyl group on sulphur lone pair ionization energies has been re-investigated by use of ab initio and semi-empirical MNDO quantum-chemical calculations. The effect of the interaction between n s and σ SiC ★ orbitals and that of electron reorganization have been shown to be unimportant in the case of silyl-methyl-sulphides. To interpret the observed features of the ionization energies and reactivity, the electron release by the β-silyl group and hyperconjugative interactions have been considered. Stabilization brought about by β-substitution for the ground state of the radical cation is ca . 10 kcal mol −1 for alkyl (10.11 kcal mol −1 ) and silyl (9.48 kcal mol −1 ) substituents at the MP2 6-31G★★//HF 6-31G★★ level of theory. The effects of the substituents are smaller on the neutral ground state of the molecules (6.80 and 0.50 kcal mol −1 for methyl and silyl groups, respectively) at the same level of theory. The observed low ionization energy of the β-silyl-substituted sulphides must be attributed to differences in the stabilization of the neutral ground states of the silyl- and alkyl-substituted derivatives rather than to the stabilization of the radical cationic ground state in the case of compounds of the type R 3 SiCH 2 SH.

Photoelectron spectroscopy study of substituent effect of halogens on the thiophene ring

Abstract The UV photoelectron spectra of 21 halogen (chloro- bromo- and iodo ) -substituted thiophenes have been studied. The assignment was based on band shapes, correlation of band positions of related compounds and CNDO/S calculations. In the case of compounds bearing iodine in the three and four positions the above considerations gave contradictory results and only the relative intensities in the HeI and HeII spectra provided decisive proof for the assignment. The substituent effect in the α positions differs considerably from that in the β position. To explain these effects a simple conjugative model was proposed. Not only does the achieved assignment fit the correlation along the chloro-bromo-iodo series well, but it also provides a simple method for constructing the electronic structure of polyhalogenated systems from simpler building blocks of molecules with a lower degree of substitution (e.g. the band structure of the tetrachloro derivative from those of 2,5-dichloro- and 3,4-dichloro-thiophenes). This proves that a consistent picture was obtained of the electronic structure of halogen thiophenes.

UPS investigation of 1-substituted pyrroles

Abstract He I UPS spectra of 1-substituted pyrroles has been investigated and interpreted using MNDO quantum-chemical calculations. The substituent effect of alkyl and silyl group on the pyrrole ring has been discussed.

Photoelectron spectroscopic investigation of perimidine derivatives

The Hel UPS spectra of acetamidine, perimidine, and four 2-substituted perimidine derivatives have been recorded and interpreted using ab initio and MNDO quantum-chemical calculations. A large interaction between the naphthalene and amidine fragment was concluded from the lowest ionization energy. The color-determining band of these compounds is strongly affected by the intramolecular charge-transfer transitions, which are of low energy because of the low ionization energy of the perimidine moiety.

Photoelectron spectroscopic investigation of phenyl isocyanato silanes

SummaryThe HeI photoelectron spectra of compounds C6H5(CH3)nSi(NCO)3−n were recorded and analysed using semiempirical AM1 quantum chemical calculations. The interaction between phenyl and pseudohalide groups is minimal. The splitting of bands originated from pseudohalide groups is not sensitive to the Si-N-C bond angle.ZusammenfassungEs wurden die Photoelektronenspektren von Verbindungen C6H5(CH3)nSi(NCO)3-n aufgenommen und die Spektren mit der Hilfe von semiempirischen quantenchemischen AM1 Rechnungen ausgewertet. Die Wechselwirkung zwischen den Phenyl- und Pseudohalogenidgruppen erwiesen sich als minimal. Die Aufspaltung der infolge der Pseudohalogenidgruppe entstandenen Bänder ist gegen den Bindungswinkel von Si-N-C unempfindlich.