Bond length–bond order relations and calculated geometries for some benzenoid aromatics, including phenanthridine. Structures of 5,6-dimethylphenanthridinium triflate, [N-(6-phenanthridinylmethyl)-aza-18-crown-6-κ5 O,O',O'',O''',O''''](picrate-κ2-O,O')potassium, and [N,N'-bis(6-phenanthridinyl-κN-methyl)-7,16-diaza-18-crown-6-κ4 O,O',O'',O''']sodium iodide dichloromethane solvate

1996 ◽  
Vol 52 (5) ◽  
pp. 823-837 ◽  
Author(s):  
R. Kiralj ◽  
B. Kojić-Prodić ◽  
M. Žinić ◽  
S. Alihodžić ◽  
N. Trinajstić
Keyword(s):  
Bond Length ◽  
Bond Order ◽  
Alkali Metals ◽  
Sodium Iodide ◽  
Complex Cation ◽  
Molecular Orbital Calculations ◽  
Benzenoid Hydrocarbons ◽  
Molecular Mechanics Calculations ◽  
Bond Lengths ◽  
Order Relations

The crystal structures of the title compounds are studied in order to investigate the role of novel fluoroionophores in complexation of sodium and potassium. In the potassium complex seven coordination, including the picrate ligand, is encountered. An additional coordination site is via the phenanthridine nitrogen at 3.252 (2) Å (second coordination). The complex is of C 1 symmetry and the aza-18-crown-6 macrocylic ring exhibits a crown-type conformation. The 7,16-diaza-18-crown-6 macrocycle accommodates a six-coordinate sodium with two additional ligands, via nitrogen from phenanthridine units. The complex cation shows a crystallographic twofold symmetry. The macrocycle is not of the crown-type conformation. In both complexes the alkali metals are shifted out of the cavity centres towards a picrate ligand in [N-(6-phenanthridinylmethyl)-aza-18-crown-6-κ5 O,O′,O′′,O′′′,O′′′′](picrate-κ2 O,O′)potassium and the phenanthridine units in [N,N′-bis-(6-phenanthridinyl-κN-methyl)-7,16-diaza-18-crown-6-κ4 O,O′,O′′,O′′′]sodium iodide dichloromethane solvate. Semi-empirical and molecular mechanics calculations based on various force fields were used for the optimization of phenanthridine geometry. The values obtained are compared with experimental data. Valence bond calculations of bond lengths in some benzenoid aromatic systems (C—C bonds in benzenoid hydrocarbons, azabenzenoid hydrocarbons and picrate-like systems; C—N bonds in the azabenzenoids; C—O bonds in the picrate-like systems), as well as some analogous Hückel molecular orbital calculations (C—C bonds in the benzenoid hydrocarbons and the azabenzenoids), were found to agree with the observed values (average differences up to 0.015 Å). These approaches can be used by means of bond length-bond order relations for prediction of bond lengths in the phenanthridine units as well as in the picrate.

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.

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.

A Correlation between Bond Length and Ionic Bond Order. Application to the Ylide–Ylene Problem

1975 ◽  
Vol 53 (20) ◽  
pp. 3040-3043 ◽  
Author(s):  
Myung-Hwan Whangbo ◽  
Saul Wolfe ◽  
Fernando Bernardi
Keyword(s):  
Bond Length ◽  
Bond Order ◽  
The Other ◽  
Atomic Charges ◽  
Bond Orders ◽  
Ionic Bond ◽  
Molecular Systems ◽  
Bond Lengths ◽  
Coulombic Repulsion ◽  
Overlap Population

The C—O and C—S bond lengths of the cations, radicals, and anions CH3O, CH3S, CH2OH, and CH2SH have been found not to correlate with the overlap populations of the C—X bonds. On the other hand, very satisfactory linear relations are observed with the ionic bond orders of the C—X bonds. It is suggested that, in certain molecular systems, it may be more meaningful to associate shortening of a bond A—B with greater coulombic attraction (or smaller coulombic repulsion) between the two point charges represented by the net atomic charges on the atoms A and B than with an increase in the overlap population between these atoms. It is noted that such an interpretation can account for the short C—P bond in a phosphonium ylide without resort to (p → d)π conjugation.

Crystal and Molecular Structure of Tris(Ethane-1,2-Diamine)Osmium(III) Trifluoromethanesulfonate Monohydrate

1987 ◽  
Vol 40 (7) ◽  
pp. 1267 ◽  
Author(s):  
PA Lay ◽  
GM Mclaughlin ◽  
AM Sargeson
Keyword(s):  
Molecular Structure ◽  
Bond Length ◽  
Oxidation State ◽  
Bond Order ◽  
Crystal And Molecular Structure ◽  
Single Bond ◽  
Bond Lengths ◽  
Formal Oxidation State ◽  
Bite Angle ◽  
Diamine Ligands

The crystal and molecular structure of racemic [Os(en)3] (CF3SO3)3.H2O has been determined. The [Os(en)3]3+ ion adopts a le ξob configuration and has approximate C2 symmetry with an Os-N(av.) bond length of 2.11 � and a bite angle for the chelate of - 82�. The previously recorded structure of the [Os(en-H)2(en)]2+ ion in which two deprotonated ethane-1,2-diamine ligands adoptoa cis configuration of the two amido donors, and in which the OsIV -N( amido ) bonds (1.90 �) are much shorter than the Os-N(amine) bonds, 2.11 ( cis ), 2.19 (trans), along with the present structure indicates a bond order > 1 for the osmiumo amido bond. The normal Os-N bond lengths fall into well defined ranges OS-NR3 (2.11-2.14 �), Os=NR2- (~1.90 �),Os=NR2 (- 1.70 �) and Os=N3-(- 1.58-1.63 �). These single bond lengths are more affected by trans effects than the formal oxidation state of the osmium centre.

THE SULPHUR–OXYGEN BOND IN SULPHURYL AND THIONYL COMPOUNDS: CORRELATION OF STRETCHING FREQUENCIES AND FORCE CONSTANTS WITH BOND LENGTHS, BOND ANGLES, AND BOND ORDERS

1963 ◽  
Vol 41 (8) ◽  
pp. 2074-2085 ◽  
Author(s):  
R. J. Gillespie ◽  
E. A. Robinson
Keyword(s):  
Bond Length ◽  
Linear Relationship ◽  
Force Constant ◽  
Bond Order ◽  
Bond Angle ◽  
Bond Orders ◽  
Bond Angles ◽  
Bond Lengths ◽  
Frequency Relationship ◽  
Oxygen Bond

It is shown that the bond length of an SO bond and the bond angle of an SO2 group may be very satisfactorily correlated with the SO stretching frequency. The bond-length – stretching-frequency relationship is used to predict some bond lengths that have not been measured and the OSO angles in some sulphuryl compounds are also calculated. The problem of defining and measuring the bond order of sulphur–oxygen bonds is discussed. It is shown that there is a linear relationship between the force constant and the bond order and a non-linear relationship between the bond length and the bond order.

XXXV.—Graphite Crystals and Crystallites. I. Binding Energies in Small Crystal Layers

1948 ◽  
Vol 62 (3) ◽  
pp. 336-349 ◽  
Author(s):  
Mary Bradburn ◽  
C. A. Coulson ◽  
G. S. Rushbrooke
Keyword(s):  
Bond Length ◽  
High Temperatures ◽  
Molecular Hydrogen ◽  
Bond Order ◽  
Resonance Energy ◽  
Binding Energies ◽  
Experimental Fact ◽  
Stable Layer ◽  
Bond Lengths ◽  
Carbon Carbon Bond

SummaryCalculations are made of the resonance energy, bond order and bond length in a series of graphitic layers of varying size. Carbon–carbon bond lengths appear to vary very little in size with increasing number of carbon atoms, in agreement with experiment. But variations in resonance energy are significant, and indicate clearly that resonance, by itself, favours an approximately square, rather than oblong, shape. But in the case of such layers in equilibrium in the presence of molecular hydrogen, the most stable layer containing a given number of carbon atoms is of the long, thin polyphenyl type. Some tentative calculations suggest that polymerisation of smaller groups to larger ones should be endothermic, in agreement with the experimental fact that the formation of larger graphitic crystallites during carbonisation occurs, with emission of hydrogen, only at high temperatures.

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

1990 ◽  
Vol 68 (7) ◽  
pp. 1051-1062 ◽  
Author(s):  
Saul Wolfe ◽  
B. Mario Pinto ◽  
Vikram Varma ◽  
Ronald Y. N. Leung
Keyword(s):  
Experimental Data ◽  
Bond Length ◽  
Molecular Orbital ◽  
Global Analysis ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Anomeric Effect ◽  
Coupling Constant ◽  
Electron Pairs ◽  
Bond Lengths

The magnitude of a one-bond C–H coupling constant depends upon the chemical environment of the hydrogen atom and, especially, upon its stereochemical relationship to vicinal lone electron pairs. However, a lone electron pair is not essential for the observation of a stereoelectronic effect, since even cyclohexane exhibits different axial and equatorial C–H coupling constants. We propose the name "Perlin Effect" to describe such observations. An analysis of the extensive experimental data regarding the Perlin Effect reveals that, in cyclohexane and in six-membered rings having one or more heteroatoms of the first row attached to the carbon of interest, 1JC–H is always larger for an equatorial hydrogen than for an axial hydrogen. The magnitude of the Perlin Effect is reduced when the carbon carrying the hydrogen of interest is attached to first row and second row atoms or heteroatoms, and it reverses when the carbon atom carries two heteroatoms from below the first row.The existence of the Perlin Effect in nuclear magnetic resonance spectra is reminiscent of an infrared effect known as the Bohlmann bands, whose origin has previously been explained by quantitative perturbational molecular orbital (PMO) theory in terms of the effects of lone electron pairs upon the lengths and strengths and, therefore, the chemical reactivities of vicinal C—H bonds. Since the magnitude of a one-bond C–H coupling constant is expected to vary inversely with bond length, the origins of the Perlin Effect and of the Bohlmann bands would seem to be the same, i.e., the longer (weaker) C—H bond has the smaller one-bond coupling constant. This expectation has now been confirmed: for 25 molecules, representing a total of 35 different kinds of C—H bonds, the bond lengths, stretching force constants, and charge distributions have been determined from fully optimized 6-31G* molecular orbital calculations. In nine of ten cases for which experimental data exist for pairs of diastereomeric or diastereotopic hydrogens, the shorter C—H bond of the pair has the larger coupling constant; in the tenth case, the experimental difference is only 1–2 Hz. Moreover, a global analysis of the data in terms of the equation J = A + BqCqH + C/r, where J is an experimental coupling constant, q is a total atomic charge, and r is a C—H bond length, correlates 23 different types of C—H bonds linearly with a correlation coefficient of 0.915. The C parameter is the leading term of the correlation. Among the systems studied theoretically are eight molecules of the type CH3CHXY (Y = OH, SH; X = F, Cl, OH, SH), which are representative of systems containing both endocyclic and exocyclic first row and second row anomeric effects. The exocyclic effect is found to be very similar for first row and second row substituents, but the endocyclic effect is larger for the first row substituent. Both findings agree with experimental data in solution. Finally, quantitative PMO analysis has been employed to analyse the origins of the different C—H bond lengths in the various molecules of the study. Keywords: anomeric effect, PMO analysis, NMR, stereochemistry, molecular orbital calculations.

scholarly journals Complex transition metal hydrides: linear correlation of countercation electronegativity versus T–D bond lengths

2015 ◽  
Vol 51 (56) ◽  
pp. 11248-11251 ◽  
Author(s):  
T. D. Humphries ◽  
D. A. Sheppard ◽  
C. E. Buckley
Keyword(s):  
Transition Metal ◽  
Bond Length ◽  
Linear Correlation ◽  
Metal Hydrides ◽  
Bond Lengths ◽  
Transition Metal Hydrides ◽  
Complex Hydrides

For homoleptic 18-electron complex hydrides, an inverse linear correlation has been established between the T–deuterium bond length and the average electronegativity of the metal countercations.

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