The Relationship between Bond Type, Bond Order and Bond Lengths. A Re-evalution of the Aromaticity of Some Heterocyclic Molecules

Heterocycles ◽  
1991 ◽  
Vol 32 (10) ◽  
pp. 2023 ◽  
Author(s):  
Vernon G. S. Box
Keyword(s):  
Bond Order ◽  
Bond Type ◽  
Bond Lengths ◽  
Heterocyclic Molecules ◽  
The Relationship ◽  
Type Bond

Bond order-bond length relationships in conjugated hydrocarbons - the microwave spectrum and structure of 3,4-dimethylenecyclobutene

1983 ◽  
Vol 36 (4) ◽  
pp. 639 ◽  
Author(s):  
RD Brown ◽  
PD Godfry ◽  
BT Hart ◽  
AL Ottrey ◽  
M Onda ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Ab Initio ◽  
Bond Length ◽  
Bond Order ◽  
Microwave Spectrum ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Bond Orders ◽  
Bond Lengths ◽  
Typical Error

The microwave spectrum of the benzene isomer 3,4-dimethylenecyclobutene including spectra of all possible single 13C-substituted and sufficient singly and doubly D-substituted species to give a complete r5 geometry, have been measured and analysed. An estimate of the re geometry has also been derived. The additional precise CC bond lengths obtained for an unsubstituted, conjugated hydrocarbon enable us to examine bond order-bond length relationships more thoroughly than has previously been possible. The CC bond lengths exhibit a noticeably better correlation with SCFMO bond orders than with simple H�ckel bond orders. Further confirmatory measurements of the dipole moment of dimethylenecyclobutene have been made. Ab initio molecular orbital calculations using a 6-31G basis set give an optimized geometry with CC bond lengths within 2 pm of the r5 values. The computed dipole moment agrees almost exactly with experiment but a corresponding calculation on fulvene is discrepant with experiment by 0.16 D, which is probably a more typical error.

Bond Localization Energy. I. Definition, Methods of Computation, and Relation to Bond Order

1949 ◽  
Vol 2 (4) ◽  
pp. 564
Author(s):  
RD Brown
Keyword(s):  
Bond Order ◽  
Theoretical Discussion ◽  
Localization Energy ◽  
Resonance Energies ◽  
The Relationship ◽  
Bond Localization ◽  
Activated Complex ◽  
Mobile Order

A new quantity-the bond localization energy-which has some advantages in the theoretical discussion of the chemical reactivities of various bonds, is introduced. Its relationship to the activated complex is indicated. It is shown to be expressible in terms of the resonance energies of certain molecules related to the molecule being considered. The various methods available for computing resonance energies by the LCAO method are outlined and some of these are used to derive numerical values for the localization energies of particular bonds. The relationship between bond localization energy and mobile order is investigated, and the significance of the relations thus found is indicated.

Accurate heats of atomization and accurate bond lengths.: II. Polyenes and polyphenyls

1968 ◽  
Vol 46 (12) ◽  
pp. 2041-2051 ◽  
Author(s):  
Donald H. Lo ◽  
M. A. Whitehead
Keyword(s):  
Steric Hindrance ◽  
Bond Order ◽  
Minimum Energy ◽  
Stabilization Energy ◽  
Direct Measure ◽  
Bond Lengths ◽  
Molecular Stability ◽  
Linear Polyenes ◽  
Substituted Polyenes ◽  
Good Agreement

Accurate heats of atomization and bond lengths are calculated for several polyenes and polyphenyls, using the s.c.f.–l.c.a.o.–m.o. method described in Part I (1). Localization of π and σ bonds is found in the linear polyenes and in the diphenyl-substituted polyenes. The estimated stabilization energy per CC bond (SECC) gives a direct measure of the π electron conjugation and σ bond compression. Conjugation stabilization and steric hindrance are analyzed in 1,3-butadiene and biphenyl; the predicted geometries are in good agreement with experimental results. The minimum energy for any planar structure is found to be associated with the s.c.f. calculated bond lengths. The validity of pi bond order as a measure of molecular stability in the polyphenyls is discussed.

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.

N-(6-Amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, valine, serine, threonine and methionine: interplay of molecular, molecular–electronic and supramolecular structures

2000 ◽  
Vol 56 (5) ◽  
pp. 882-892 ◽  
Author(s):  
J. N. Low ◽  
M. D. López ◽  
P. Arranz Mascarós ◽  
J. Cobo Domingo ◽  
M. L. Godino ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Three Dimensional ◽  
Computational Modelling ◽  
Carboxyl Groups ◽  
Molecular Electronic ◽  
Database Analysis ◽  
Intermolecular Hydrogen Bonds ◽  
Bond Lengths ◽  
The Relationship ◽  
Derivatives Of

In each of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C10H15N5O4 (3) (orthorhombic, P212121), N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C8H11N5O5·H2O (4) (orthorhombic, P212121), and N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C9H13N5O5(5) (monoclinic, P21), the C-nitroso fragments exhibit almost equal C—N and N—O bond lengths: the C—N range is 1.315 (3)–1.329 (3) Å and the N—O range is 1.293 (3)–1.326 (3) Å. In each compound there are also very short intermolecular O—H...O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O...O distances range from 2.440 (2) to 2.504 (4) Å and the O—H...O angles lie between 161 and 163°. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)–(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).

STUDY OF INVARIANT Tc IN HIGHER DOPING LEVEL Y1-xCaxBa2-xLaxCu3Oy

2005 ◽  
Vol 19 (01n03) ◽  
pp. 307-309 ◽  
Author(s):  
X. F. SUN ◽  
H. L. DU ◽  
X. F. RUI ◽  
L. ZHANG ◽  
F. WANG ◽  
...  
Keyword(s):  
Structural Change ◽  
Carrier Concentration ◽  
Doping Level ◽  
Narrow Range ◽  
Bond Lengths ◽  
The Relationship

The higher doping level Y 1-x Ca x Ba 2-x La x Cu 3 O y samples were synthesized with x from 0.25 to 0.55. Structure and superconductivity have been investigated. Comparing with the results of lower doping level, the Tc of these samples keeps almost constant when dopant increasing. While some structural characters, such as Cu (1)- O (4), Cu (2)- O (4) bond lengths change randomly in a narrow range. The relationship between Ba / La position and Tc is rather interesting. The results give another evidence that the influence of structural change on superconductivity is independent of carrier concentration.

scholarly journals Bond lengths in naphthalene and anthracene

1951 ◽  
Vol 207 (1090) ◽  
pp. 306-320 ◽  
Keyword(s):  
Aromatic Hydrocarbon ◽  
Bond Length ◽  
Configuration Interaction ◽  
Bond Order ◽  
Bond Orders ◽  
Bond Lengths ◽  
Self Consistent ◽  
Hydrocarbon Molecules ◽  
Experimental Values ◽  
Correction Terms

An extremely careful inquiry is made into the possibility of predicting bond lengths in condensed aromatic hydrocarbon molecules. Agreement with the best experimental values, such as those of Robertson, Abrahams, White, Mathieson and Sinclair, is fairly easily obtained to an accuracy of about 0.02Å. This shows that the concept of fractional bond order may quite properly be used to infer bond lengths. Both the molecular-orbital and resonance methods are equally good for this purpose. Predictions to within less than 0.02Å require the introduction of new factors usually neglected. No less than five such factors are discussed: ( а ) electrostatic forces, arising from possible differences in electronegativity of the various carbon atoms, ( b ) changes of bond orders due to electronegativity differences, ( c ) variation of resonance integrals with bond length, ( d ) obtaining a self-consistent set of resonance integrals, ( e ) inclusion of configuration interaction. Correction terms which result from these improvements lie between 0 and 0.015Å, and are not all of the same sign. It is unlikely therefore that this type of analysis will be able to give confident predictions of bond lengths to less than 0.01Å.

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