Bond lengths characteristic

AX(B)680) suggested therefore that the unassociated (32) exhibits bond lengths characteristic of pyridin-2-one in the gas phase and thus is the best model for MO calculations. 

A wide range of stable metallic and molecular complexes of tetrazole systems, e.g. (3), has been described <77AHC(21)323) and many crystal structures have been determined for these complexes. The tetrazole ring is invariably planar with bond lengths characteristic of an aromatic system. Tetrazolate anion salts (4) are stable aromatic systems and they have been used widely as nucleophiles in synthetic reactions. 

It is not possible to apply (C2.1.1) down to the level of monomers and replace by the degree of polymerization N and f by the sum of the squares of the bond lengths in the monomer because the chemical constitution imposes some stiffness to the chain on the length scale of a few monomer units. This effect is accounted for by introducing the characteristic ratio defined as C- — The characteristic ratio can be detennined... 

Theoretical analysis of certain features in the electromagnetic spectrum yields basic molecular parameters such as bond lengths and bond stiffness. We shall see presently that the mechanical spectra can be related to molecular parameters and not just modelistic characteristics as we have used until now. 

Transition-metal complexes of the thionylimide anion exhibit characteristic vibrations in the regions 1260-1120, 1090-1010 and 630-515 cm , which are assigned to Oas(NSO), Os(NSO) and <5(NSO), respectively. X-ray structural data for several M-NSO complexes reveal N-S and S-O bond lengths of ca. 1.46 0.04 A indicative of double bond character in both of these bonds. 

The tetramethylammonium salt [Me4N][NSO] is obtained by cation exchange between M[NSO] (M = Rb, Cs) and tetramethylammonium chloride in liquid ammonia. An X-ray structural determination reveals approximately equal bond lengths of 1.43 and 1.44 A for the S-N and S-O bonds, respectively, and a bond angle characteristic bands in the IR spectrum at ca. 1270-1280, 985-1000 and 505-530 cm , corresponding to o(S-N), o(S-O) and (5(NSO), respectively. Ab initio molecular orbital calculations, including a correlation energy correction, indicate that the [NSO] anion is more stable than the isomer [SNO] by at least 9.1 kcal mol . ... 

One or more parameter sets that fit the equations and atom types to experimental data. Parameter sets define force constants, which are values used in the equations to relate atomic characteristics to energy components, and structural data such as bond lengths and angles. 

A large body of experimental evidence confirms that covalent bonds have characteristic distances depending on bond type. Carbon-carbon single and double bond lengths are around 1.54A and 1.32A, respectively, while partial double bond distances, e.g., in benzene, are about 1.40A. 

Electron transfer into the LUMO might also cause bonding changes. What are the CBr bonding characteristics of the LUMO in methyl bromide Is it bonding (one surface extends over the bond) or antibonding (two surfaces meet in middle of the bond) How would electron transfer from a nucleophile affect the CBr bond length ... 

How close are the two nuclei in the H2 molecule If they are too close, they will repel each other because both are positively charged, yet if they re too far apart, they won t be able to share the bonding electrons. Thus, there is an optimum distance between nuclei that leads to maximum stability (Figure 1.9). Called the bond length, this distance is 74 pm in the H2 molecule. Every covalent bond has both a characteristic bond strength and bond length. 

In general, increasing the temperature within the stability range of a single crystal structure modification leads to a smooth change in all three parameters of vibration spectra frequency, half-width and intensity. The dependency of the frequency (wave number) on the temperature is usually related to variations in bond lengths and force constants [370] the half-width of the band represents parameters of the particles Brownian motion [371] and the intensity of the bands is related to characteristics of the chemical bonds [372]. 

Each atom makes a characteristic contribution, called its covalent radius, to the length of a bond (Fig. 2.21). A bond length is approximately the sum of the covalent radii of the two atoms (36). The O—H bond length in ethanol, for example, is the sum of the covalent radii of H and O, 37 + 74 pm = 111 pm. We also see from Fig. 2.21 that the covalent radius of an atom taking part in a multiple bond is smaller than that for a single bond of the same atom. 

Li, Liu and Lu investigated the electronic structures and the possible aromaticity of some 10 r-electron systems, including the dication, at the HF/6-31G level [118]. The optimised S-S bond length of is 210 pm. Based on the analysis of the bonding characteristics in terms of the canonical molecular orbital and the Foster-Boys localized molecular orbital, they concluded that is of weak aromaticity. This is due to the occupation of the weak antibonding MOs. As a consequence, the bond strengths of the 10 r-electron systems decrease with respect to their 6 r-electron counterparts. 

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