Double bonds bond lengths

Fig. 2.6-5. Calculated structures of the most stable P6 and Pg isomers [8, 11]. Note that Pg includes a double bond. Bond lengths were obtained at the BP86/SVP level [23], For comparison at the same level the P-P bond length of P4 is 223 pm and close to the experimental value of 221 pm [35],...

Of greater relevance catalytically is that the combined use of l3C enrichment and 13C nutation NMR spectroscopy can distinguish between proposed rival mechanisms for the Ziegler-Natta catalyzed polymerization of acetylene. In the four-center insertion mechanism the enriched acetylene (HC =C H) is incorporated as shown in Scheme 6. It is to be noted that the, 3C—13C bond label is here incorporated into a carbon-carbon double bond, the length of which is significantly smaller than that of a carbon-carbon single bond, which is how the enriched acetylene would be incorporated in the two-center mechanism shown in Scheme 7. The results of nutation experiments leave little doubt that the Ziegler-Natta polymerization of acetylene proceeds by a four-center mechanism. 

The crystal structure shows the expected E geometry of the double bond. The length of the silicon-potassium bond (3.45 A) lies within the range observed for similar anionic compounds [3]. The length of the carbon-carbon olefinic bond is not significantly affected by the adjacent anionic silicon atom, in contrast to the spectroscopic behavior of this bond (see below). 

These structures are known as resonance structures. The true structure is some weighted average of these three. That is, each N-0 bond is between a single and double bond in length, as is the N-N bond. In order to rank the relative importance of each structure, we need to use formal charges. Formal charge, FC, is an arbitrary property. We define the formal charge on a specific atom by... 

X-ray studies show that in the crystal the molecule is non-planar and has alternate single and double bonds of length 1-46 and 1-34 A respectively [47]. The molecules in the crystal have alternate cis... 

The l,3,4-triphospha-2-silabutene skeleton results from [(Mes P)2SiBu-tJ and Ph2PCl and provides yellow crystals stable enough to give the first X-ray structure of a Si=P double bond, of length 209.4 pm and shorter than the other Si-P bond of 225.4 pm. The P=Si-P-P skeleton is... 

Carbon dioxide has a linear structure. The simple double-bonded formula, however, does not fully explain the structure since the measured carbon-oxygen bond lengths are equal but intermediate between those expected for a double and a triple bond. A more accurate representation is, therefore, obtained by considering carbon dioxide as a resonance hybrid of the three structures given below ... 

All the carbon-oxygen bonds are found to be of equal length and intermediate between carbon-oxygen single and double bond length. 

The sulphite ion, SO3, has a pyramidal structure and the short S—O bond length suggests the presence of double bonding, i.e. 

In the sulphate ion, the four oxygen atoms are tetrahedrally arranged round the sulphur atom, at equal distances hence all the S—O bonds are identical, and their short length suggests that they are double bonds (as in SOj, SO3, and SO3") ... 

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