A Linear Relationship Between Bond Orders and Stretching Force Constants

Robinson, E. A.; Lister, M. W.

doi:10.1139/v63-439

Cited by 29 publications

(8 citation statements)

References 20 publications

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“…2.3–2.7 mdyn/Å (see the Supporting Information for a full analysis). This value is lower that reported for the corresponding bond in the DBMP 2 dimer (3.6 mdyn/Å) and ethane (4.5 mdyn/Å), but it is significantly larger than the values determined for the longest C(sp 3 )–C(sp 3 ) bond reported to date (1.806 Å, 1.08 mdyn/Å) and for a multicenter bond in a dianionic tetracyanoethylene dimer (0.45 mdyn/Å) . The force constant calculated for 4 2 would thus correspond to a bond of medium strength, which is however weaker than conventional C(sp 3 )–C(sp 3 ) bonds.…”

Section: Resultscontrasting

confidence: 65%

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical

et al. 2020

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A 139-π-electron nanographenoid radical was obtained by expanding the periphery of a naphthalimide–azacoronene hybrid with a methine bridge. The radical was isolated in the form of its σ-dimer, which was shown to possess a conformationally restricted two-layer structure both in the solid state and in solution. The dimer is cleaved into its parent radicals when exposed to ultraviolet or visible radiation in toluene solutions but is resistant to thermally induced dissociation. Under inert conditions, the radicals recombine quantitatively into the σ-dimer with observable kinetics, but they are oxidized into a ketone derivative in the presence of atmospheric oxygen. Combined structural, spectroscopic, and theoretical evidence shows that the σ-dimer contains a weak C(sp 3 )–C(sp 3 ) bond, but is stabilized against thermal dissociation by a very strong dispersive interaction between the overlapping π surfaces.

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Section: Resultscontrasting

confidence: 65%

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical

et al. 2020

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“…Vibrational force constants have a linear correlation with bond order; therefore, these values offer another means of characterizing the Mo-E bond. 21 Using the harmonic oscillator approximation, we found a force constant of 3.87 mdyne Å −1 for 1-As and 4.02 mdyne Å −1 for 1-P. These values are approximately half of the 7.86 mdyne Å…”

Section: Scheme 1 Synthesis Of 1-asmentioning

confidence: 78%

A Terminal Molybdenum Arsenide Complex Synthesized from Yellow Arsenic

2009

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“…The compound [14]annulene is one of a series of annulenes studied by Sondheimer.70 Its room temperature nmr spectrum was found71 to consist of two sharp singlets at 5 5.58 and 6.07 in a ratio of about 6:1. This has been attributed72 to the existence of two conformational isomers, 5 and 6.…”

Section: Resultsmentioning

confidence: 99%

“…fairly close to being so. [14][15][16] Unfortunately, for CspS-Cgpi bonds the only useful experimental data available are the ethylene ks of 9.6 X 10-5 dyn/cm17 and a benzene ka of 7.6 X 10-5 dyn/cm.18 Assuming a linear relationship, a plot of pn vs. ka results in a force constant of 3.6 X 10-5 dyn/cm for a Csp2-Csp2 single bond (ptJ = 0) which is considerably below Herzberg's Cspi-Csp! constant of 4.5 X 10-5 dyn/cm.17 This seems intuitively incorrect since the overlap of sp2 and sp3 orbitals is almost identical at distances of 1.5-2.0 Á.…”

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confidence: 99%

Conformational analysis. XC. Calculation of the structures of hydrocarbons containing delocalized electronic systems by the molecular mechanics method

Allinger¹,

Sprague²

1973

J. Am. Chem. Soc.

302

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The molecular mechanics method for structure determination has been extended to hydrocarbons containing delocalized systems by including a quantum mechanical (VESCF) -system calculation in the iterative sequence, from which bond orders are obtained. A relationship between stretching force constant and bond order is found, so the force constants can be calculated from the bond orders, and the delocalized molecule is then handled in the standard way. Torsional constants are calculated from the planar molecule, and then the molecule is allowed to deform to the geometry corresponding to an energy minimum. Thus the method is applicable to nonplanar systems as well as to planar systems. It is applied to many simple compounds (butadiene, benzene, biphenyl, naphthalene, etc.), and then to more complicated systems such as -di-terí-butylbenzene, pregeijerene, the annulenes, and bridged annulenes. Insofar as experimental data are available, the agreement with experiment is generally good. In a few cases structural predictions are made. Previouspapers have described a force field method for the calculation of the structures and energies of saturated hydrocarbons,5 ketones,6 and olefins.7 There seems no doubt that the method is generally applicable to the calculation of the structures of molecules, but there are areas where special problems occur, ones which require something substantially more than the kind of treatment used in the cases discussed. Aromatic compounds, and other compounds containing delocalized systems, are found to present such problems. Hydrocarbons will be dealt with in this paper, and the extension to other kinds of compounds such as unsaturated ketones, etc., will be the subject of subsequent papers.The basic problem can perhaps best be seen by considering some simple examples. If one wishes to treat a delocalized system such as benzene by the force field method, as long as one knows the force constants, the method is straightforward. For benzene, since all of the bonds are equivalent, the force constants can be evaluated by standard methods. They can then be applied to those benzene derivatives where the substituents on the benzene are not sufficient to interrupt the conjugated electronic system so as to change any stretching constants or natural bond lengths or angles. However, if one considers the naphthalene molecule as another example, one finds the following. If the ben-(1) This is paper XC in the series "Conformational Analysis" [paper LXXXIX:

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A Linear Relationship Between Bond Orders and Stretching Force Constants

Cited by 29 publications

References 20 publications

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical

A Terminal Molybdenum Arsenide Complex Synthesized from Yellow Arsenic

Conformational analysis. XC. Calculation of the structures of hydrocarbons containing delocalized electronic systems by the molecular mechanics method

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