Multiple bond density

The extent of multiple-bond densities increases with bond order compared to a single-bond pair, although treated as a single pair. 

Sigma bond A chemical bond in which electron density on the intemudear axis is high, as with all single bonds. In a multiple bond, one and only one of the electron pairs forms a sigma bond, 188-189... 

Bond paths are observed between bonded atoms in a molecule and only between these atoms. They are usually consistent with the bonds as defined by the Lewis structure and by experiment. There are, however, differences. There is only a single bond path between atoms that are multiply bonded in a Lewis structure because the electron density is always a maximum along the internuclear axis even in a Lewis multiple bond. The value of pb does, however, increase with increasing Lewis bond order, as is shown by the values for ethane (0.249 au), ethene (0.356 au), and ethyne (0.427 au), which indicate, as expected, an increasing amount of electron density in the bonding region. 

Why is the complex OsHCl(CO)(P Pr3)2 stable, when it is unsaturated It has been argued that lone pairs on the alpha atom of a ligand M—X (M is a transition metal) can have a major influence on reactivity and structure. If M has empty orbitals of appropriate symmetry, X M tt donation creates an M—X multiple bond, with consequent transfer of electron density to M decreasing its Lewis acidity.23 The presence of a carbonyl ligand in OsHCl(CO)(P Pr3)2) increases the n-donor capacity of chloro by means of the push-pull effect making this molecule not a truly 16-valence electron species. 

The osmium-carbyne carbon bond lengths for the three complexes do not differ significantly, and reference to Table IV indicates that these distances are distinctly shorter than the characterized metal-carbon double bonds of osmium carbene and carbonyl complexes. In both osmium alkylidene and carbyne complexes, then, the metal-carbon multiple bond lengths are largely insensitive to changes in the metal electron density (cf. Section IV,B). 

The data given in Table 13.3 show that the extent of bond shortening is greatest for B-F bonds. This is to be expected because back donation of electron density from F to B is more effective when the donor and acceptor atoms are of comparable size. The following resonance structures are used to represent the multiple bonding between B and F ... 

In the preceding chapters we have seen how new bonds may be formed between nucleophilic reagents and various substrates that have electrophilic centres, the latter typically arising as a result of uneven electron distribution in the molecule. The nucleophile was considered to be the reactive species. In this chapter we shall consider reactions in which electrophilic reagents become bonded to substrates that are electron rich, especially those that contain multiple bonds, i.e. alkenes, alkynes, and aromatics. The jt electrons in these systems provide regions of high electron density, and electrophilic reactions feature as... 

The V=0 stretching frequency is an important characteristic of oxovanadium(IV) complexes, generally observed at 985 50 cm-1.353,355 It is quite sensitive to the nature of the ligands. Donors that increase the electron density of the metal reduce its acceptor properties towards O, the V—O multiple bond character and the stretching frequency. For complexes VOL , v(V=0) falls in the order L = H20 > NCS- > CN- > DMSO F this series bears no obvious relation to the spectrochemical and nephelauxetic series.353... 

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