STERIC INHIBITION OF RESONANCE: III. CALCULATION OF RESONANCE ENERGIES AND BOND LENGTHS

1959 ◽  
Vol 37 (5) ◽  
pp. 905-914 ◽  
Author(s):  
James Trotter
Keyword(s):  
Nitro Group ◽  
Bond Order ◽  
Electron Distribution ◽  
Resonance Energy ◽  
Nitro Compounds ◽  
X Ray ◽  
Bond Lengths ◽  
Resonance Energies ◽  
Aromatic Nitro ◽  
Steric Inhibition Of Resonance

In many aromatic nitro compounds steric effects prevent the attainment of complete coplanarity and inhibit resonance interaction between the nitro group and the aromatic π-electrons. The variations with nitro group tilt of resonance energy, electron distribution, and π-bond order in this type of molecule have been calculated by molecular orbital methods, and the corresponding bond length variations have been deduced. The calculated bond lengths for 9,10-dinitroanthracene and 9-nitroanthracene are compared with those measured by X-ray analyses.

A Novel Example of X-Ray-Radiation-Induced Chemical Reduction of an Aromatic Nitro-Group-Containing Thin Film on SiO2 to an Aromatic Amine Film

ChemPhysChem ◽  
2003 ◽  
Vol 4 (8) ◽  
pp. 884-889 ◽  
Author(s):  
Paula Mendes ◽  
Maura Belloni ◽  
Mark Ashworth ◽  
Chris Hardy ◽  
Kirill Nikitin ◽  
...  
Keyword(s):  
Thin Film ◽  
Nitro Group ◽  
Aromatic Amine ◽  
Chemical Reduction ◽  
X Ray ◽  
Radiation Induced ◽  
Aromatic Nitro

Simple Synthesis of Dimethyl Nitrobenzhydrylphosphonates and Heteroarylnitroarylacetonitriles via Vicarious Nucleophilic Substitution (VNS) Reaction

Synthesis ◽  
2020 ◽  
Vol 53 (01) ◽  
pp. 175-181
Author(s):  
Mieczysław Mąkosza ◽  
Małgorzata Bechcicka ◽  
Krzysztof Wojciechowski
Keyword(s):  
Nucleophilic Substitution ◽  
Nitro Group ◽  
Nitro Compounds ◽  
Simple Synthesis ◽  
Para Position ◽  
Crucial Step ◽  
Vicarious Nucleophilic Substitution ◽  
Aromatic Nitro Compounds ◽  
Leaving Group ◽  
Aromatic Nitro

Acetals of dimethyl phenyl- and heteroaryl-α-hydroxymethanephosphonates were deprotonated to generate carbanions, which enter the vicarious nucleophilic substitution (VNS) of hydrogen in aromatic nitro compounds to form 4-nitrobenzhydrylphosphonates and α-heteroaryl-4-nitrobenzylphosphonates. Similarly acetals of cyano­hydrins of heteroaromatic aldehydes (furfural and 2-formylthiophene) react to form heteroaryl 4-nitroarylacetonitriles. The anion of the hemiacetal of acetaldehyde is an efficient leaving group in the base-induced β-elimination step – the crucial step in the VNS reaction. The reaction selectively occurred at the para-position to the nitro group.

Bond Lengths in Conjugated Molecules: The Present Position

1951 ◽  
Vol 207 (1088) ◽  
pp. 91-100 ◽  
Keyword(s):  
Bond Order ◽  
Empirical Relation ◽  
Simple Theory ◽  
Reliable Estimate ◽  
Present Position ◽  
Conjugated Molecules ◽  
X Ray ◽  
Bond Lengths ◽  
Hydrocarbon Molecules ◽  
Semi Empirical

A survey is given of the present methods for calculating bond lengths in conjugated molecules. Except in simple cases this has to be achieved by combining a calculated bond order with a semi-empirical relation between order and length. There are several definitions of bond order in current use, some of which can be shown to be less valuable than others. Recent accurate X -ray analysis has shown convincingly that the concept of bond order is a valid one, though there are limits to the degree of accuracy that may be claimed. Several possible improvements upon the simple theory are mentioned, most of which indicate alterations in bond lengths calculated from the simple theory, of the order of 0.005 Å. It is concluded that for condensed hydrocarbon molecules, the lengths of individual bonds may be predicted to within about 0.015 Å. For heteromolecules there are still too many additional factors for any reliable estimate to be possible.

scholarly journals Chloroantimonate(III), IV. Darstellung und Kristallstruktur von 2,2′-Bipyridinium-pentachloroantimonat (C10H8N2H2)SbCl5 und der metastabilen Modifikation von 4,4′ -Bipyridinium-pentachloroantimonat (C10H8N2H2)SbCl5 / Chloroantimonates(III), IV. Preparation and Crystal Structures of 2,2′-Bipyridinium Pentachloroantimonate (C10H8N2H2)SbCl5 and of the Metastable Modification of 4,4′-Bipyridinium Pentachloroantimonate (C10H8N2H2)SbCl5

1983 ◽  
Vol 38 (12) ◽  
pp. 1615-1621 ◽  
Author(s):  
Annegret Lipka
Keyword(s):  
Single Crystal ◽  
Diffraction Analysis ◽  
Crystal Structures ◽  
Bond Order ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Distorted Octahedral ◽  
Intermolecular Contacts

2,2′-Bipyridinium pentachloroantimonate (III) and the metastable modification of 4,4′-bipyridinium pentachloroantimonate(III) were synthezised and investigated by single crystal X-ray diffraction analysis. The structures consist of 2,2′-bipyridinium and 4,4′-bipyridinium cations, respectively, and of pentachloroantimonate anions. With regard to bonding and short intermolecular contacts the coordination of the Sb atoms is distorted octahedral in both structures. Bond lengths of equivalent Sb-Cl bonds differ strongly within the structure of the 2,2′-bipyridinium salt (239.9 pm to 312.1 pm) and are not distinguishable from short intermolecular contacts (305.4 pm and 321.8 pm). In the structure of the 4,4′-bipyridinium salt, bond distances vary only from 240.9 pm to 267.8 pm and are clearly below intermolecular contacts at 318.2 pm. In spite of the different distances the total bond order for each Sb atom is 3. In the structure of the 2,2′-bipyridinium salt the anions build tetramers, whereas in the structure of the 4,4′-bipyridinium salt the anions form chains

STERIC INHIBITION OF RESONANCE: V. NITROMESITYLENE

1959 ◽  
Vol 37 (9) ◽  
pp. 1487-1490 ◽  
Author(s):  
James Trotter
Keyword(s):  
Crystal Structure ◽  
Nitro Group ◽  
Aromatic Ring ◽  
Resonance Interaction ◽  
Vibration Frequencies ◽  
X Ray ◽  
Planar Model ◽  
Steric Inhibition Of Resonance

A detailed X-ray investigation of the crystal structure of nitromesitylene has shown that the nitro group is twisted 66° out of the plane of the aromatic ring about the C—N bond. The resulting decrease in resonance interaction compared with a completely planar model has been correlated with the characteristic NO2 vibration frequencies.

Studies on the rearrangement of ortho-nitrobenzylidenemalonates and their Analogues to 2-aminobenzoate derivatives

2002 ◽  
Vol 80 (2) ◽  
pp. 192-199 ◽  
Author(s):  
Elzbieta Lewandowska ◽  
Stefan Kinastowski ◽  
Stanislaw F Wnuk
Keyword(s):  
Double Bond ◽  
Nitro Group ◽  
Phenyl Ring ◽  
Nitro Compounds ◽  
Trifluoromethyl Group ◽  
Reverse Polarity ◽  
Michael Reactions ◽  
Carbon Double Bond ◽  
Oxidative Rearrangement ◽  
Aromatic Nitro

Reaction of the diethyl 2-nitro-4-(trifluoromethyl)benzylidenemalonate with diethylamine in alcohols resulted in the reduction of the nitro group and the oxidation of the vinylic carbon attached to the phenyl ring. Simultaneous migration of the malonic fragment gave the appropriate 2-amino-4-(trifluoromethyl)benzoate esters. The presence of at least two nitro groups, or one nitro group and trifluoromethyl group on the phenyl ring, attached to the α-carbon and strongly electron withdrawing substituents at the β-carbon (CO2Et, CN) in ortho-nitrobenzylidene systems is necessary for this reductive–oxidative rearrangement to proceed. Reaction of nitrocinnamates with thiols in the presence of triethylamine in tetrahydrofuran gave Michael addition products with different regioselectivity of addition. Ethyl 2-nitrocinnamate undergoes standard β-addition of thiols to a carbon–carbon double bond. However, 2,4-dinitro- and 2,4,6-trinitrocinnamates undergo α-addition of thiols, indicating that the presence of two nitro groups on the phenyl ring can reverse polarity of the carbon–carbon double bond in cinnamate acceptors.Key words: abnormal Michael reactions, aromatic nitro compounds, benzylidene compounds, rearrangements.

A solvent effect on the conformation of aromatic nitro groups

1967 ◽  
Vol 20 (11) ◽  
pp. 2381 ◽  
Author(s):  
ID Rae
Keyword(s):  
Solvent Effect ◽  
Nitro Group ◽  
Nitro Compounds ◽  
Dimethyl Sulphoxide ◽  
Aromatic Nitro Compounds ◽  
Aromatic Nitro

The differences between proton mangetic resonance spectra of aromatic nitro compounds in deuterochloroform and dimethyl sulphoxide solutions are interpreted in terms of increased steric requirements of the nitro group in the latter solvent. In suitably ortho-substituted aromatic nitro compounds this leads to twisting of the nitro group about the Ar- N bond.

The crystallography of the biscyclic dibenzacridines I. The electron distribution in 1.2:8.9-dibenzacridine

1960 ◽  
Vol 258 (1294) ◽  
pp. 302-318 ◽  
Keyword(s):  
Electron Distribution ◽  
Crystal And Molecular Structure ◽  
Molecular Orbital Theory ◽  
Two Dimensional ◽  
Orbital Theory ◽  
X Ray ◽  
Bond Lengths ◽  
Molecular Arrangement ◽  
Difference Density ◽  
The Mean

The crystal and molecular structure of 1.2:8.9-dibenzacridine has been determined by a least-squares refinement of the complete two-dimensional X-ray data. The average estimated standard deviations of the carbon-carbon and carbon-hydrogen bond lengths are 0·009 and 0·08Å respectively, the mean C—H bond length in the molecule being 1·08Å. The observed ‘difference’ density and bond lengths are compared with predictions based on molecular-orbital theory. The molecular arrangement in the crystal is discussed in relation to the calculated charge distribution in the molecule.

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