Bond angle and distance

FIGURE 5 1 (a) The planar framework of u bonds in ethylene showing bond distances and angles (b) and (c) The p orbitals of two sp hybridized carbons overlap to produce a tt bond (d) The electrostatic potential map shows a region of high negative potential due to the tt elec trons above and below the plane of the atoms... 

Tetrazine, hexahydro-bond distances and angles, 3, 541 colour, 3, 541... 

Structural Studies. X-ray powder diffraction patterns for I indicate that the crystal structure is isomorphous to Zr2(0H)2-(SOO3 (H20)>. Figure 1 depicts the structure of the zirconium compound (5). The structure of I is identical to that of the zirconium analog except for variations in bond distances and angles which do not affect the overall structure. We have as yet been unable to obtain single crystals of I which are suitable for X-ray diffraction studies. 

The distances between atoms in a molecule are characteristic properties of the molecule and can give us information if we compare the same bond in different molecules. The chief methods of determining bond distances and angles are X-ray diffraction (only for solids), electron diffraction (only for gases), and spectroscopic methods, especially microwave spectroscopy. The distance between the atoms of a bond is not constant, since the molecule is always vibrating the measurements obtained are therefore average values, so that different methods give different results. However, this must be taken into account only when fine distinctions are made. 

Molecular orbital calculations, whether by ab initio or semiempirical methods, can be used to obtain structures (bond distances and angles), energies (such as heats of formation), dipole moments, ionization energies, and other properties of molecules, ions, and radicals—not only of stable ones, but also of those so unstable that these properties cannot be obtained from experimental measurements." Many of these calculations have been performed on transition states (p. 279) this is the only way to get this information, since transition states are not, in general, directly observable. Of course, it is not possible to check data obtained for unstable molecules and transition states against any experimental values, so that the reliability of the various MO methods for these cases is always a question. However, our confidence in them does increase when (1) different MO methods give similar results, and (2) a particular MO method works well for cases that can be checked against experimental methods. ... 

Thousands of dipole moments, with references, are collected in McClellan, Tables of Experimental Dipole Moments , vol. 1, W.H. Freeman, San Francisco, CA, 1963 vol. 2, Rahara Enterprises, El Cerrita, CA, 1974. Tables of Interatomic Distances and Configurations in Molecules and Ions , London Chemical Society Special publication no. 11, 1958, and its supplement. Special publication no. 18, 1965, include bond distances and angles for hundreds of compounds, along with references. 

Figure 1. Bond distances and angles for 2,7-dichlorodibenzo-p-dioxin. The molecule is situated on an inversion center.

Figure 3. Bond distances and angles for the two independent molecules in 2,3,7,8-tetrachlorodihenzo-p-dioxin. Both molecules are located on crystallographic inversion centers.

Figure 1.20 (a) Thermal ellipsoid plot and bond distances and angles of [Au2(2,6-Me2Ph-form)2].2Hg(CN)2-2THF. (b) 2D of [Au2(2,6-Me2Ph-form)2].2Hg(CN)2 2THF showing the TFIF solvent in the voids. 

Table 3 Halogen bond distances and angles in various salts with I3...

Fig. 4. Thermal ellipsoidal drawing45 of [Li(12-crown-4)2]+ [Trip2GaGaTrip2]. Important bond distances and angles for this compound, and its aluminum analog, are given in Table II.

M.O. Calculations. The serai-empirical molecular orbital calculations were made using the UHF INDO model developed by Pople and co-workers (13), which incorporates the one-center exchange integral. Additionally, instead of assuming standard values for bond distances and angles, full geometry optimization at the INDO level was employed (14). Thus the results do not depend upon an arbitrary choice for the molecular geometry. 

L. Schafer, M. Cao, and M. J. Meadows, Predictions of Protein Backbone Bond Distances and Angles from First Principles, Biopol., 35 (1995) 603-606. 

Predictions of Protein Backbone Bond Distances and Angles from First Principles... 

---