Intramolecular Bond Length

Hettema H, Wormer P E S and Thakkar A J 1993 Intramolecular bond length dependence of the... 

The first use of the CSD was the determination of average intramolecular bond lengths. These are now coded for all types of chemical bond [21], and such reference values are so well established that any bond length determination at variance with them is presumably wrong. Intramolecular geometry is hardly a frontier topic any more. 

Wormer PES, Hettema H, Thakkar AJ (1993) Intramolecular bond length dependence of the anisotropic dispersion coefficients for H2-rare gas interactions. J Chem Phys 98 7140-7144... 

Fujii et al.30 have reported experimental evidence for the molecular dissociation process in Br2 near 80 GPa. This transition, which is coincident with the onset of pressure-induced metallization, was first discovered in molecular/metallic iodine.3 A diatomic molecular crystal loses its molecular character in the limit when the intermolecular distance becomes equal to the intramolecular bond length. Fujii et al.30 applied the Herzfeld criterion to I2 and Br2 and estimated that the molar reffactivity reaches the atomic limit around 20 GPa in I2 and 80 GPa in B12. In both cases, the computed pressure coincides with that for molecular dissociation accompanied by metallization. 

Among other original interpretations of room-temperature structural results, we may quote here the work of Flandrois and Chasseau [72], who have evaluated the amount of charge transfer in TCNQ-based salts by means of the study of combinations of intramolecular bond lengths (see Section VII. C). 

Direct methods. The charge per molecule is measured either directly (e.g., very accurate structural determination, x-ray photoelectron spectroscopy) or through the relative change of an intramolecular parameter sensitive to the charge (e.g., intramolecular bond length, intramolecular vibration frequency). The accuracy is relatively poor ( 10%). 

A similar approach can be tried on other molecules. For example, Kobayashi et al. [150] and Fettouhi [151] have tabulated some intramolecular distances in BEDT-TTF molecules as a function of the charge transfer. However, the use of combinations of intramolecular bond lengths lead to results less sensitive to experimental errors (D. Chasseau, private communication, 1993). 

Table 17. Selected intramolecular bond lengths and angles...

Sette, F., J. Stohr, and A. P. Hitchcock (1984). Correlation between intramolecular bond lengths and X-shell u-shape resonances in gas-phase molecules. Chem. Phys. Lett. 110, 517-20. 

How about intramolecular bond lengths and bond angles in the supramolecular structured... 

This rule is also obeyed by molecules with homonuclear bonds (25) (except by molecular oxygen). For example the intramolecular I—I-distance in gaseous iodine is 267.6 pm (27). However, in the solid state the interaction between the molecules as characterized by the intermolecular distance of 354 pm induces an increase in intramolecular bond length to 271.5 pm (25). 

The properties of the linear chain of atoms fall into three sets those for the intramolecular, the intermolecular and the closed-shell Ne-H interactions. The intramolecular bond lengths vary from Re = 1.39 au, the equilibrium value to 1.04 au obtained for the central molecule in the Ne H6 Ne vise at a pressure of 158 GPa. Only at the highest pressures do the intermolecular separations approach Re. Unlike the LDA calculations on solid hep hydrogen, no increase in separation over Re is found for high pressures. The Ne-H separations decrease at a slower rate. 

Besides intramolecular bond lengths and angles, the crystal packing and intermolecular contacts of some of the substituted benzofuroxans have been discussed.65 68... 

With atomic species, the near edge structure is of no further interest. With molecular adsorbates, the near edge X-ray absorption is dominated by intramolecular transitions (/X- and (7-resonances). Their dependency on the polarization provides information on the orientation of the molecule. From the energy of the a-resonance intramolecular bond lengths, tab can be estimated for simple molecules. Figure 5.97 shows an X-ray absorption spectrum of NO adsorbed on a nickel surface. 

NEXAFS spectra are frequently dominated by intramolecular resonances of ti or polarization dependence of these resonances can be used to determine the orientation and intramolecular bond lengths of the molecule on the surface. NEXAFS probes the element specific empty electronic states and has local electronic and bonding structure sensitivity. The orientation of the molecules can be determined using angular resolved spectra and analysis of the 71 resonances. 

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