Klaus Kowski

Photoelectron Spectra, Electronic Structures, and Conformational Properties of (E)-Stilbene, Styrylthiophenes, and (Thienylethenyl)pyridines

The UV photoelectron spectra of two isomeric styrylthiophenes (5, 6) and six isomeric (thienylethenyl)pyridines (7−12) have been recorded and analyzed, making use of DFT Becke3LYP calculations. The spectra were compared with those of (E)-stilbene (1e) and the isomeric styrylpyridines (2−4), which are π-isoelectronic with 5−12. Using quantum chemical analyses, planar molecular structures were obtained for all these compounds. However, from the separation ΔIP of the ionization bands associated with the π7 and π3 MOs, it is possible to make a distinction between planar and twisted molecular structures. Accordingly in these compounds, 2-substituted pyridine rings and 3-substituted thiophene rings are nearly untwisted, whereas phenyl rings, 3- and 4-substituted pyridine, and 2-substituted thiophene rings are twisted to an extent similar to that in 1e. The apparent distortion of the molecules is probably caused by torsional vibrations, so that twisted average geometries correspond to planar equilibrium structures. The B3LYP data permit detailed conclusions to be drawn with regard to the conformational preferences of 2- and 3-substituted thiophene and pyridine rings in heterocyclic analogues of 1e, as well as the to relative stabilities of isomers 7−12. The results clearly indicate that PE spectroscopy is a powerful method for analysis of conformational properties of stilbene-like molecules.

Reactivity of Lewis acids towards nitriles; crystal structure and electron deformation density of C2N2·SbF5 and photoelectron spectrum of AsF5

The reactivity of nitriles and dinitriles HCN, C2N2, CCl2(CN)2 and CH2(CN)2 towards AsF5 and SbF5 has been investigated. The new compounds HCN·AsF51, HCN·SbF52, C2N2·AsF53, C2N2·SbF54, CH2(CN)2·AsF55, CH2(CN)2·(2AsF5)6 and CCl2(CN)2·AsF57 have been characterized by chemical analysis, IR, Raman, 1H, 19F and 14N NMR spectroscopy. The crystal structure of the first example of a cyanogen adduct C2N2·SbF54 has been determined. Compound 4 crystallizes in the orthorhombic space group C2221 with cell parameters a= 6.579(1), b= 16.245(1) and c= 6.389(1)A. The deformation density of the molecule was examined. The reactivities of HCN and C2N2 towards the strong Lewis acid AsF5 are discussed on the basis of the hard–soft acid–base principle. The hitherto unknown ionization potential of AsF5(15.57 eV) was obtained by photoelectron spectroscopy. A semiquantitative molecular orbital scheme for AsF5 is presented.

Spectroscopic and theoretical studies on intramolecular OH–π hydrogen bonding in 4-substituted 2-allylphenols

2-Allylphenol (1) constitutes a mixture of conformers, in which an OH-pi hydrogen bonded closed (1a) and open form (1b) can be distinguished. 4-Substituted 2-allyphenols (2-9) have been synthesised and investigated by theoretical and spectroscopic methods. In 1-9, the energy and the structure of the hydrogen bonds show distinct variation with substituents. In the PE spectra of most compounds, two ionisations can be distinguished which are related to the allylic pi(C[double bond]C) orbitals of the two conformers a and b and differ in energy by DeltaIP(C[double bond]C). Alternatively, DeltaIP(C[double bond]C) can be determined indirectly from comparison of the PE spectra of the respective phenols and anisoles with the same substituents. DeltaIP(C[double bond, length as m-dash]C) values between 0.3 and 1.1 eV were found. Frequency shifts Deltanu(OH) of the O-H vibration in CHCl3 solution were measured by IR spectroscopy. By means of correlation analysis of the relationship between the strength of the intramolecular hydrogen bond, DeltaIP(C[double bond]C), Deltanu(OH) values and substituent constants it is established how substituents in 4-position affect the intramolecular OH-pi hydrogen bond. The investigations demonstrate that the DeltaIP(C[double bond]C) data can be used as descriptors for this intramolecular interaction.

New indigo chromophores containing disulfide donor groups

Abstract Oxidative dimerization of a mixture of the thiolanone 5 and the dithiolanone 4 yields 2c as chromophore of thioindigo 1c, and 6 and 7 as chromophores of still unknown indigo dyes. As compared to 2c, the first ionization potential of the new indigo chromophore 7 is higher, but the calculated HOMO-LUMO splitting is lower. Accordingly, its longest wavelength absorption maximum surpasses that of 2c distinctly.

RAFT polymers for protein recognition

Summary A new family of linear polymers with pronounced affinity for arginine- and lysine-rich proteins has been created. To this end, N-isopropylacrylamide (NIPAM) was copolymerized in water with a binding monomer and a hydrophobic comonomer using a living radical polymerization (RAFT). The resulting copolymers were water-soluble and displayed narrow polydispersities. They formed tight complexes with basic proteins depending on the nature and amount of the binding monomer as well as on the choice of the added hydrophobic comonomer.

Electronic structure and gas-phase thermolysis of 4-substituted 3,3,5,5-Tetramethyl-3,5-dihydro-4H-pyrazoles studied by photoelectron spectroscopy. First evidence for an alkylideneselenirane☆

The electronic structures of the tetramethyldihydropyrazoles [(I; R=Se,S:O, NNH2, NN:CMe2) and II] have been studied by photoelectron spectroscopy and interpreted with the aid of semi-empirical SCF MO calcns. (PM3). Gas-phase pyrolyzes of I and II have been carried out and analyzed by photoelectron spectroscopy. Both I(R =Se, S:O) and in part I(R=NNH2) eliminate mol. nitrogen to form reactive species which cyclize to three-membered rings, i.e. the novel alkylideneselenirane III, the alkylidenethiirane S-oxide IV, and the cyclopropanone hydrazone V, resp., which decomp. at higher temps. The elusive alkylideneselenirane III was studied by IR spectroscopy in an argon matrix at 10 K.

Photoelectron Spectra, Electronic Structures, and Conformational Properties of Substituted 2‐Styrylpyrroles

The UV photoelectron spectra of three pairs of cis/trans-isomers of 2-(2-methylstyryl)pyrroles (1-6) have been recorded and analysed, making use of density functional theory (DFT) calculations at the B3LYP level. Compounds 1 and 2 have no further substituents in the pyrrole ring. In the other compounds the pyrrole ring is substituted by a methyl group in the 1-(3,4) or 5-position (5,6). Twisted conformations were calculated for 1-6 in which the toluene ring is generally much more distorted from the plane of the central C=C double bond than the pyrrole ring. In the cis-isomers (2, 4, 6) the torsion angle of the toluene groups amounts to about 50 o, while in the trans-isomers (1, 3, 5) the torsional angle is only about half as large. The energy difference delta IP values of the ionization bands associated with the molecular orbitals (MOs) pi7 and pi3 is related to torsion. Calculated delta IP values are generally 5-10 % larger than the experimental values, indicating that torsional vibrations contribute to the apparent distortion of the molecules. The results clearly indicate that PE spectroscopy - in combination with high-level quantum chemical calculations - is a verasatile method to distinguish E/Z isomers of heterocyclic stilbene-like molecules.

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.

Structure elucidation of the photoproducts obtained by the photolysis of N-acetyl-2-styrylpyrroles

Abstract From the irradiation mixture of N -acetyl-2-styrylpyrroles ( 5a , b ) the deacylated ( 6a , b ), phototransposition ( 7a , b – 10a , b ), electrocyclisation ( 12 ), addition and reduction ( 11 , 13 and 14 ) and dimerisation products ( 15 ) have been detected. No intramolecular cycloaddition products have been observed.

Structural chemistry of polycyclic heteroaromatic compounds. Part 10: photoelectron spectra and electronic structures of 1-substituted 1H-benzotriazoles☆

Abstract The electronic structures of 1H-benzotriazole (1) and its 1-substituted derivatives 2–20 have been investigated by ultraviolet photoelectron spectroscopy and quantum chemical methods. The conformational properties of some compounds were studied by semi-empirical and B3LYP calculations. For the alkenyl derivative 14 a twisted conformation was ascertained both from IP values and calculations, and in the amino derivative 20 the amino group is twisted by 90° which is reflected by the absence of n/π interactions. With only a few exceptions, the ionization potentials corresponding to the five occupied π MOs (π1–π5) and the two n(N) orbitals of the 1H-benzotriazole unit (Bt1) could be determined and assigned for 1–20. Linear free energy correlations of the IPs related to these orbitals with inductive substituent parameters σI and F were satisfactory except for IP(π3). The energies of π and n MOs—except for π3—are thus affected primarily by the substituents electronegativity. The different behaviour of π3 is caused by direct interactions with substituent orbitals. For some substituents for which no σI or F parameters were known these could be determined from their IPs by correlation analysis.