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Carbon-13 nuclear magnetic resonance configurational assignments are made for a free-radical polystyrene sample examined at 25.033 MHz and 140°C. The spectra of the aromatic C 1 and methylene were examined. New assignments were established based strictly on a oneparameter Bernoullian fit that was in satisfactory agreement with the relative intensities of the peaks observed.

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The methyl group is connected to the carbyne-carbon by a normal single bond [149(2) pm]. The Cr-C-CH, arrangement appears to be linear, even though F , calculations with disordered bent molecular models show no influence on the R factor provided that the angular deviation does not exceed 5 .(CO)@"CHj)3](Br)CrCCH, (3) crystallizes with two crystallographically independent molecules in the asymmetric unit of the cell. Both independent molecules have identical geometries within experimental error. Mean values of the bond lengths are: Cr-CC-0 193(4), Cr-Br 260.3(5). Cr-P 239.6(9) pm. The Cr-CcarhYne separation [ 168(3) pm] is almost identical with that in (2). The deviation of the Cr-C-CH3 group from linearity is not significant {177(3) 3. Table 2 shows some bond lengths for chromium and tungsten complexes with metal-carbon single bonds, metal-carbene bonds which can be regarded as partial double bonds, and the new metal-carbyne bonds.The metal-carbyne carbon bonds are shorter by cu. 40pm than a metal-carbon single bond in the case of tungsten and by cu. 50pm in the case of chromium. For comparison, the shortening in the series alkane, alkene and alkyne is 33pm (ethane 154. ethylene 134, acetylene 121 pm)["'. The extremely short metal-carbon separation in the compounds of this study supports the proposition of a metal-carbon triple bond.