| MadSci Network: Chemistry |
The values for the bond lengths as determined in the gas phase can be found at the following web site and at others. http://www.sciencemag.org/cgi/content/abstract/254/5030/410 "On the basis of this symmetry assumption, least-squares refinement of a model incorporating all possible interatomic distances led to the values of (C1-C2) = 1.458(6) angstroms (Å) for the thermal average bond length within the five-member ring (that is, for the bond fusing five- and six- member rings) and rg(C1-C6) = 1.401(10) Å for that connecting five-member rings (the bond fusing six-member rings). The weighted average of the two bond lengths and the difference between them are the values 1.439(2) Å and 0.057(6) Å, respectively. The diameter of the icosahedral sphere is 7.113 (10) Å. The uncertainties in parentheses are estimated 2 values." All of the bonds in any 5 membered ring in the "buckyball" structure are equivalent and thus should be the same length - the 1.401 value. If you check on the bonds in any 6 membered ring, they alternate between being common to a 5 membered ring (1.401) and being common to another 6 membered ring (1.439). Even though there may be delocalization, there is not a hard and fast rule that would say that the bond lengths have to be the same value in the 6 membered ring. Although this is may not be an exact analogy, I would not expect the length of the C-C bond common to both rings in indene would be the same as the lengths of the other C-C bonds in the 6 membered ring. The fact that both values in the "buckyball" are between the usual values for a C-C (1.54 A) and the C=C (1.33 A) would seem to indicate that each has some degree of delocalization. If this is not a convincing answer, get back to me at: Dr. Jerry Franzen jtfranzen@fuse.net
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