Herman J. Geise

Ab initio studies of structural features not easily amenable to experiment: Part III. The influence of lone pair orbital interactions on molecular structure☆

Abstract The characteristic structural asymmetries and distortions of AXYB systems in which an electron lone pair is at Y are discussed on the basis of the completely relaxed ab initio equilibrium geometries of a number of representative systems including various conformations of methanediol, hydrazine, 1,2-dimethylhydrazine and of compounds with CH 3 groups adjacent to OH, OCH 3 , NH, NCH 3 and C(π). It is found that, regardless of quantitative overlap and energy gap factors, all calculated trends in the relative extensions of bond distances and bond angles can be correlated in every detail to qualitative predictions based only on the orientational aspects of orbital interaction concepts.

Alkoxylated p-phenylenevinylene oligomers: synthesis and spectroscopic and electrochemical properties

Twenty-one n-alkoxy substituted phenylenevinylene oligomers were synthesized, varying in size, number and position of the OR groups. IR,MS and solubility data are presented. NMR measurements provided the molecular structure as well as information about conformations and molecular dynamics. UV and of cyclic voltammetric data give correlations of chemical structure (number and position of OR substituents) with separate HOMO and LUMO energies.

Blue electroluminescent devices with high quantum efficiency from alkoxy‐substituted poly(para‐phenylene vinylene)‐trimers in a polystyrene matrix

We report electroluminescence of electroluminescent devices fabricated from cis,trans‐ 2,5‐dimethoxy‐1,4 ‐bis[2‐(3,4,5‐trimethoxyphenyl)ethenyl]benzene blended in a polystyrene matrix as emission layer. This choice of materials avoids the inherently poor miscibility of polymers with other compounds and minimizes interactions between the host polymer and the electro‐optically active guest, which can produce quenching sites. A blue light‐emitting device with high internal quantum efficiency (∼1%) results.

Ab initio studies of structural features not easily amenable to experiment: Part 8. The structural consequences of the anomeric effect in compounds with disubstituted tetrahedral carbon atoms

Abstract The geometries of three conformations of FCH 2 OH and four conformations each of NH 2 CH 2 NH 2 and NH 2 CH 2 OH are completely refined by ab initio calculations on the 4–21G level. It is found that most characteristic structural and conformational properties of such systems can be reliably predicted on the basis of a simple anomeric orbital interaction model. The extension of this model to all compounds in which two electronegative substituents with non-bonding lone pairs or bonding π-electrons are attached to the same tetrahedral carbon atom, including polymer systems such as proteins, seems to be useful.

Structure of gaseous methyl acetate as determined by joint analysis of electron diffraction, microwave and infrared spectroscopy, supplemented by a valence force field and constraints from geometry relaxed ab initio calculations

Abstract The structure of methyl acetate was studied by joint analysis of gas phase electron diffraction, microwave and IR data, using constraints taken from relaxed 4-21G gradient geometry and force field calculations. All data are in accord with a planar heavy-atom skeleton in the syn conformation. The geometry of methyl acetate in the gas phase is essentially equal to that in the crystal. Some r g — r e corrections have been evaluated. Subject to the ab initio constraints the following internal coordinates ( r 0 α structure) have been found: CO = 1.206 A, H 3 CO = 1.438 A, CO = 1.357 A, CC = 1.496 A, 〈CH〉 = 1.078 A, ∠COC = 116.4°, ∠;OCO = 123.0°.

The molecular structure of pyridine in the gas phase determined from electron diffraction, microwave and infrared data and ab-initio force-field calculations

Abstract The gas-phase molecular structure of pyridine was studied by joint analysis of electron diffraction, microwave and infrared data, augmented by vibrational constraints taken from force-field calculations at the 4-21G ab-initio level. Geometrical constraints arising from 4-21G, 4-31G, 4-21GN* and microwave results were tested. The 4-21GN* constraints were significantly better than the others. The range of models that fit all available experimental data was then investigated with respect to the difference between the CNC and NCC valence angles. This resulted in the following best-fitting model ( r g distances, r 0 α angles): NC = 1.344 A; C 2 C 3 = 1.399 A; C 3 C 4 = 1.398 A; CH (average) = 1.094 A; CNC = 116.1°; NCC = 124.6°; C 2 C 3 C 4 = 117.8°; C 3 C 4 C 5 = 119.1°; NCH = 115.2°. The data suggest that the perturbation resulting from the N atom is primarily in the CNC part of the ring.

The molecular structure of gaseous methyl vinyl ether at room temperature, studied by molecular orbital constrained electron diffraction and microwave spectroscopy

Abstract The gas phase molecular structure of methyl vinyl ether at room temperature has been studied by joint analysis of electron diffraction and microwave data. Constraints on geometrical and thermal parameters were derived from the geometry and force field of the s-cis form, obtained by ab-initio calculations (4–21 G basis set) after complete geometry relaxation. A range of models was investigated that fits all available data (infrared, microwave and electron diffraction). The following r g / r α -parameters were obtained: CC: 1.337 A, C( sp 2 )O: 1.359 A, C( sp 3 )O: 1.427 A, : 1.102 A ∠CCO : 127.3° and ∠COC: 116.8°. Experimental r g  r e (ab initio) corrections are given for CC, C( sp 2 )O and C sp 3 )O. This investigation demonstrates that molecular orbital constrained electron diffraction is sufficiently reliable and in such a manner that it can be applied to more complicated problems.

Structure determination of propanal by joint analysis of gas electron diffraction, microwave and infrared spectroscopy, including constraints and a valence force field from geometry relaxed ab-initio calculations

Abstract The structure and conformational equilibrium of CH 3 -SYN and CH 3 -SKEW conformers of propanal were studied by joint analysis of gas electron diffraction, microwave and infrared data, including constraints obtained after ab-initio relaxations (4-21G basis set) of the molecule. A valence force field was calculated for both conformers and scaled upon experimental IR frequencies; theoretical frequencies and band intensities are compared to experimental ones. Rotamer populations of CH 3 -SYN and CH 3 -SKEW were found to be 81 and 19%, respectively, at 300 K. The following best-fitting r g / r α parameters were obtained as: r (OC) = 1.209(4) A, r (C2C3) = 1.515(9) A, r (C3C4) = 1.521(9) A for CH 3 -SYN and (with lower reliability) 1.569(45) A for CH 3 -SKEW, = 1.127(4) A, ∠O=CC = 124.5(3)°(SYN) and 125.1(3)° (SKEW), ∠CCC = 113.8(4)° (SYN) and 110.2(4)° (SKEW), torsion angle around C2C3 = 123.7(2.6)° for CH 3 -SKEW.

The molecular structure of S-triazine in the gas phase determined from electron diffraction, infrared/raman data and ab initio force field calculations

Abstract The gas phase molecular structure of s-triazine has been determined from electron diffraction data. Experimental vibrational parameters proved consistent with those from the 4-21G force field after scaling onto infrared/Raman frequencies, as well as after direct scaling on electron diffraction data. The analysis resulted in the following r g / r ° α -parameters CN = 1.338(1) A, CH = 1.106(8) A, ∠CNC = 113.9(1), ∠NCN = 126.1, ∠HCN = 116.9. The (new) r g – r e (4-21G) correction for aromatic CN is 0.006(1) A.

Solids modeled by abinitio crystal field methods. X. Structure of α‐glycine, β‐glycine, and γ‐glycine using a 15‐molecule cluster

The structure of three polymorphic forms of glycine in the crystal phase, α‐glycine (P21/n), β‐glycine (P21), and γ‐glycine (P32), was completely optimized with standard gradient procedures using a point charge model and using a model constituted of a 15‐molecule cluster surrounded by point charges. The calculations were performed with a 6‐31G basis set and in the SCF step of the calculations the MIA approach was used. The results for the 15‐molecule cluster are in better agreement with the experimental results than the results obtained with the point charge model.