Bond length calculation

Table 2.6 Comparison of Observed Bond Lengths and Bond Lengths Calculated from the Sum of Covalent Radii...

Fig. 10.12 (a) Transition state structures (C—C bond lengths) calculated at two levels for the concerted and step-wise Diels-Alder reaction shown in Fig. 10.11 (Houk, K. N., Gonzalez, J., and Li, Y,Accts. Chem. Res. 28, 81 (1995). The parenthesized values show results for calculations at a much higher (and much more expensive) level, (b) Calculated secondary deuterium isotope effects, kH/kD (per D) for the concerted and stepwise Diels-Alder reactions shown in Fig. 10.11 (Houk, K. N., Gonzalez, J., and Li, Y,Accts. Chem. Res. 28, 81 (1995). The parenthesized values show results for calculations at a much higher (and much more expensive) level)...

Two nonequivalent bond lengths calculated for the model complex [NbH2(SiH2Cl)CpJ. At 173 K. 

Limiting (6-311+G basis set) Hartree-Fock bond lengths in the compounds examined are consistently shorter than experimental distances, the same result as seen for multiple bonds in hydrocarbons. Results obtained using the 6-31G basis set are nearly identical, which suggests that the 6-31G model closely reflects the Hartree-Fock limit insofar as bond length calculations for these types of systems. 

A good structure determination, as well as having a low value, will also have low standard deviations on both the atomic positions and the bond lengths calculated from these positions. This is probably a more reliable guide to the quality of the refinement. 

The bond strain in this chapter, as in most other places in this book, is defined as the difference between the observed bond lengths and the bond lengths calculated from the theoretical bond valences. A bond strain index that measures this strain is defined in eqn (12.1). 

It must be possible to choose parameters for the unit cell and atomic coordinates that reproduce as closely as possible the ideal bond lengths calculated using the network equations (3.3) and (3.4), without bringing any atoms into too close contact. 

The molecular orbital bond length calculations, although based on a planar model, show no marked differences from those obtained experimentally, probably because the molecular distortion is not severe. No significant extensions of the bonds BC (1-48 0-03 A) and GH (1-46 0-03 A) were detected, but the accuracy of the analysis does not exclude the possibility that they may occur. 

There have been several molecular orbital treatments of the structure and reactivity of oxazole these are summarized by Turchi and Dewar (75CRV389). Table 1 lists the a, it and net charge distributions calculated by the all-valence ab initio method, the net charges obtained by the MINDO/3 method and the bond lengths calculated by the latter method. 

The astute reader will have noticed that it is possible to perform an entire bond length calculation on a four deep stack without the removal of intermediate results. However in order to take full advantage of this fact we require an Am9511A which has its own individual control processor or microsequencer. 

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