Dipole moments and conformation of α-disulphones. The gauche effect

1985 ◽  
Vol 50 (10) ◽  
pp. 2245-2251 ◽  
Author(s):  
Otto Exner ◽  
Václav Jehlička
Keyword(s):  
Dihedral Angle ◽  
Graphical Method ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Statistical Treatment ◽  
X Ray ◽  
Gauche Effect

The dipole moments of substituted diphenyl disulphones I-III were measured in benzene solution and interpreted by the previously described graphical method. The results suggest an equilibrium of the ap and sc conformations in the ratio 3 : 1, at variance with various empirical rules and theories of the so-called gauche effect. A statistical treatment of X-ray data of various sulphonyl derivatives revealed essentially two preferred conformations: the more stable sc, with a broadened dihedral angle, and the less stable ap.

The gauche effect on conformation. α-Substituted sulfones and N-substituted sulfonamides

1979 ◽  
Vol 44 (11) ◽  
pp. 3378-3384 ◽  
Author(s):  
Otto Exner ◽  
Jan B. F. N. Engberts
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Conformational Preference ◽  
Electron Pairs ◽  
Gauche Effect

The dipole moments of α-halogenosulfones IIa-f in benzene solution revealed the conformation C, those of N-methyl-N-nitrosulfonamides IIIa-c the conformation F. In either case the conformational preference is governed by the gauche rule which may be worded in a modified version that symmetrical positions of polar bonds and/or of lone electron pairs are disfavoured. A lone electron pair appears to be more significant than a polar bond.

Dipole moments and conformation of peroxy esters

1981 ◽  
Vol 46 (2) ◽  
pp. 490-497 ◽  
Author(s):  
Božo Plesničar ◽  
Otto Exner
Keyword(s):  
Dipole Moment ◽  
Dihedral Angle ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Ester Group ◽  
Model Compounds ◽  
Tert Butyl ◽  
Butyl Esters

Dipole moments of sixteen substituted peroxybenzoic esters III, IV were measured in benzene solution and interpreted in terms of the conformation around the O-O bond. The dipole moment of the CO3R group is different for R = methyl and R = tert-butyl, viz. 9.0 and 10.4 . 10-30 C m, respectively. Its solution into components was carried out making reference to the dipole moments of substituted benzoic esters as model compounds. As a result the dihedral angle τ = C-O-O-C was estimated to 160-180° in the case of tert-butyl peroxy esters IV and to 110-150° in the case of methyl peroxy esters III. The mesomeric dipole moment expressing the conjugation within the ester group was estimated to 0.8 or 1.5 . 10-30 C m for methyl or tert-butyl esters, respectively.

Chalkogenolat-Ionen und ihre Derivate, V Kristall- und Molekülstruktur von 2.8-Dimethyldibenzo [c.g] [1.2.5.6] tetrathiacyclooktadien, einem Oxidationsprodukt von 4-Methylbenzol-1.2-dithiol/Chalcogenolates and their Derivatives, V Crystal and Molecular Structure of 2.8-Dimethyldibenzo[c,g][1,2,5,6]tetrathiaocin, an Oxidation Product of 4-Methylbenzene-1,2-dithiol

1979 ◽  
Vol 34 (1) ◽  
pp. 48-51 ◽  
Author(s):  
Jürgen Kopf ◽  
Klaus von Deuten ◽  
Bahman Nakhdjavan ◽  
Günter Klar
Keyword(s):  
Molecular Structure ◽  
Dihedral Angle ◽  
Oxidation Product ◽  
Crystal And Molecular Structure ◽  
X Ray ◽  
The Mean ◽  
Ray Methods ◽  
Anti Form

Abstract The structure of 2,8-dimethyldibenzo[c,g][1,2,5,6]tetrathiaocin (1b) has been determined by X-ray methods and discussed in connection with the preferred conformations of diaryl disulfides. The compound has the anti-form I. The SS-distance is 205.8 pm, the mean CSS-angle 104.1°, and the CSS/SSC-dihedral angle 111.1°.

scholarly journals Relation between photochromic properties and molecular structures in salicylideneaniline crystals

2012 ◽  
Vol 68 (3) ◽  
pp. 297-304 ◽  
Author(s):  
Kohei Johmoto ◽  
Takashi Ishida ◽  
Akiko Sekine ◽  
Hidehiro Uekusa ◽  
Yuji Ohashi
Keyword(s):  
Dihedral Angle ◽  
Steric Hindrance ◽  
Molecular Structures ◽  
Dihedral Angles ◽  
Clear Correlation ◽  
X Ray Diffraction ◽  
Photochromic Properties ◽  
X Ray ◽  
Benzene Rings ◽  
The Relationship

The crystal structures of the salicylideneaniline derivatives N-salicylidene-4-tert-butyl-aniline (1), N-3,5-di-tert-butyl-salicylidene-3-methoxyaniline (2), N-3,5-di-tert-butyl-salicylidene-3-bromoaniline (3), N-3,5-di-tert-butyl-salicylidene-3-chloroaniline (4), N-3,5-di-tert-butyl-salicylidene-4-bromoaniline (5), N-3,5-di-tert-butyl-salicylidene-aniline (6), N-3,5-di-tert-butyl-salicylidene-4-carboxyaniline (7) and N-salicylidene-2-chloroaniline (8) were analyzed by X-ray diffraction analysis at ambient temperature to investigate the relationship between their photochromic properties and molecular structures. A clear correlation between photochromism and the dihedral angle of the two benzene rings in the salicylideneaniline derivatives was observed. Crystals with dihedral angles less than 20° were non-photochromic, whereas those with dihedral angles greater than 30° were photochromic. Crystals with dihedral angles between 20 and 30° could be either photochromic or non-photochromic. Inhibition of the pedal motion by intra- or intermolecular steric hindrance, however, can result in non-photochromic behaviour even if the dihedral angle is larger than 30°.

Synthese der Amide M[N(SiMetBu2)(SitBu3)] (M = Li, Na) durch N2-Eliminierung aus den Triazeniden M[tBu3SiNNNSiMetBu2] (M = Li, Na) / Synthesis of the Amides M[N(SiMetBu2)(SitBu3)] (M = Li, Na) by N2-Elimination Reaction of the Triazenides M[tBu3SiNNNSiMetBu2] (M= Li, Na)

2007 ◽  
Vol 62 (10) ◽  
pp. 1285-1290 ◽  
Author(s):  
Hans-Wolfram Lerner ◽  
Inge Sänger ◽  
Kurt Polborn ◽  
Michael Bolte ◽  
Matthias Wagner
Keyword(s):  
Solid State ◽  
Ambient Temperature ◽  
Benzene Solution ◽  
Elimination Reaction ◽  
X Ray

The thermolabile triazenides M[tBu3SiNNNSiMetBu2] (M = Li, Na) are accessible from the reaction of tBu2MeSiN3 with the silanides MSitBu3 (M = Li, Na) at −78 °C in THF. At r. t. N2 elimination from the triazenides M[tBu3SiNNNSiMetBu2] (M = Li, Na) takes place with the formation of M[N(SiMetBu2)(SitBu3)] (M = Li, Na). X-Ray quality crystals of Li(THF)[N(SiMetBu2)(SitBu3)] (orthorhombic, Pna21) are obtained from a benzene solution at ambient temperature. In contrast to the structures of the unsolvated silanides MSitBu3 (M = Li, Na), the THF adduct Li(THF)3SitBu3 is monomeric in the solid state (orthorhombic, Pna21).

4-(Bromomethyl)benzophenone

2007 ◽  
Vol 63 (3) ◽  
pp. o1188-o1189 ◽  
Author(s):  
Wei-Jian Xu ◽  
Yang-Ling Zang ◽  
Guo-Liang Wu ◽  
Sheng-Pei Su ◽  
De-Yue Qiu
Keyword(s):  
Crystal Structure ◽  
Carbon Tetrachloride ◽  
Dihedral Angle ◽  
Structure Analysis ◽  
Title Compound ◽  
Crystal Packing ◽  
Crystal Structure Analysis ◽  
X Ray ◽  
Compound C ◽  
Phenyl Rings

The title compound, C14H11BrO, was synthesized by the reaction of 4-methylbenzophenone and bromine in carbon tetrachloride. X-ray crystal structure analysis reveals that the benzene and phenyl rings form a dihedral angle of 59.53 (6)°, and the crystal packing is stabilized by intermolecular C—H...π interactions.

Dipole moments induced in larger molecule. Long-chain aliphatic esters

1982 ◽  
Vol 47 (1) ◽  
pp. 29-34 ◽  
Author(s):  
Otto Exner ◽  
Ayfer Bapçum
Keyword(s):  
Benzene Solution ◽  
Dipole Moments ◽  
Straight Chain ◽  
Basic Assumptions ◽  
Donor Acceptor ◽  
Eyring Theory ◽  
Aliphatic Esters ◽  
Long Chain

Dipole moments of straight-chain aliphatic esters Ia-Ic and IIa-IIf were measured in benzene solution. The observed trends are poorly reproduced by the classical Smith-Eyring theory; the reason may be partly the unknown conformation, partly even donor-acceptor complexes with the solvent. No deviations were observed with the highest members of the series, attributable to violation of some basic assumptions of the theory of dielectrics.

Are mesoionic compounds aromatic?

1998 ◽  
Vol 76 (6) ◽  
pp. 869-872 ◽  
Author(s):  
Alfredo Mayall Simas ◽  
Joseph Miller ◽  
Petrônio Filgueiras de Athayade Filho
Keyword(s):  
Experimental Evidence ◽  
Key Words ◽  
Dipole Moments ◽  
The Other ◽  
Side Chain ◽  
Theoretical Studies ◽  
X Ray Diffraction ◽  
Ring Plane ◽  
X Ray ◽  
Single Bonds

We have evaluated the experimental evidence relevant to the structure and character of mesoionic compounds, accumulated for more than 100 years and including X-ray diffraction studies. We have also evaluated relevant theoretical studies. All these, including our own extensive work, lead us to conclude that mesoionic compounds are not aromatic. According to our recent definition “mesoionic compounds are planar five-membered heterocyclic betaines with at least one side chain whose α-atom is also in the ring plane and with dipole moments of the order of 5 D. Electrons are delocalized over two regions separated by what are essentially single bonds. One region, which includes the a-atom of the side chain is associated with the HOMO and negative π-charge whereas the other is associated with the LUMO and positive π-charge.” Key words: mesoionic compounds, betaines, aromaticity.

scholarly journals Directionality of light absorption and emission in representative fluorescent proteins

2020 ◽  
Vol 117 (51) ◽  
pp. 32395-32401
Author(s):  
Jitka Myšková ◽  
Olga Rybakova ◽  
Jiří Brynda ◽  
Petro Khoroshyy ◽  
Alexey Bondar ◽  
...  
Keyword(s):  
Light Wave ◽  
Fluorescent Proteins ◽  
Dipole Moments ◽  
Biological Processes ◽  
Transition Dipole ◽  
X Ray ◽  
Emission Transition ◽  
Transition Dipole Moments ◽  
Fluorescent Molecules ◽  
Incoming Light

Fluorescent molecules are like antennas: The rate at which they absorb light depends on their orientation with respect to the incoming light wave, and the apparent intensity of their emission depends on their orientation with respect to the observer. However, the directions along which the most important fluorescent molecules in biology, fluorescent proteins (FPs), absorb and emit light are generally not known. Our optical and X-ray investigations of FP crystals have now allowed us to determine the molecular orientations of the excitation and emission transition dipole moments in the FPs mTurquoise2, eGFP, and mCherry, and the photoconvertible FP mEos4b. Our results will allow using FP directionality in studies of molecular and biological processes, but also in development of novel bioengineering and bioelectronics applications.

scholarly journals Soft X-ray nanospectroscopy for quantification of X-ray linear dichroism on powders

2021 ◽  
Vol 28 (4) ◽  
Author(s):  
Selwin Hageraats ◽  
Mathieu Thoury ◽  
Stefan Stanescu ◽  
Katrien Keune
Keyword(s):  
Fresnel Zone ◽  
Dipole Moments ◽  
Fundamental Property ◽  
Linear Dichroism ◽  
Model Parameters ◽  
Transition Dipole ◽  
X Ray ◽  
Zno Powders ◽  
The Individual ◽  
Absorption Features

X-ray linear dichroism (XLD) is a fundamental property of many ordered materials that can for instance provide information on the origin of magnetic properties and the existence of differently ordered domains. Conventionally, measurements of XLD are performed on single crystals, crystalline thin films, or highly ordered nanostructure arrays. Here, it is demonstrated how quantitative measurements of XLD can be performed on powders, relying on the random orientation of many particles instead of the controlled orientation of a single ordered structure. The technique is based on a scanning X-ray transmission microscope operated in the soft X-ray regime. The use of a Fresnel zone plate allows X-ray absorption features to be probed at ∼40 nm lateral resolution – a scale small enough to probe the individual crystallites in most powders. Quantitative XLD parameters were then retrieved by determining the intensity distributions of certain diagnostic dichroic absorption features, estimating the angle between their transition dipole moments, and fitting the distributions with four-parameter dichroic models. Analysis of several differently produced ZnO powders shows that the experimentally obtained distributions indeed follow the theoretical model for XLD. Making use of Monte Carlo simulations to estimate uncertainties in the calculated dichroic model parameters, it was established that longer X-ray exposure times lead to a decrease in the amplitude of the XLD effect of ZnO.

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