Carbon coupling constants bond angle

A detailed study of the C02- species on MgO has been carried out by Lunsford and Jayne 26). Electrons trapped at surface defects during UV irradiation of the sample are transferred to the CO2 molecule upon adsorption. By using 13C02 the hyperfine structure was obtained. The coupling constants are axx - 184, am = 184, and a = 230 G. An analysis of the data, similar to that carried out in Section II.B.2 for N02, indicates that the unpaired electron has 18% 2s character and 47% 2p character on the carbon atom. An OCO bond angle of 125° may be compared with an angle of 128° for CO2- in sodium formate. 

Carbon-Proton Coupling Constant. One of the best characterized structure-spectra correlations comes from the relationship between Jch one-bond coupling constants and the bond angles about carbon. This relationship has been extended to calculate percent. r-character of the bonding orbital at carbon and ultimately to arrive at the state of hybridization. ... 

The X-ray crystal structure determination of bis[2,2,4,4,6,6-hexamethyl-2,4,6-trisilacy-clohexyljzinc (45) shows that this compound exists as a monomer in the solid state (Figure 22). The observed Zn—C bond distance of 1.937(2) A is remarkably short. The zinc atom is located at a crystallographic inversion centre and consequently enforces a perfectly linear C—Zn—C arrangement. The Zn—C(l)—Si and Si—C—Si bond angles of 110 and 117°, respectively, indicate that a considerable planarization of C(l) has occurred. That such a planarization of the carbon atoms bound to zinc is most likely also present in the structure of 45 in solution was concluded from their exceptional low field shift of 13 ppm and the small J( C- H) and 7( C- Si) coupling constants observed in its C NMR spectrum. 

Due to the partial n character of the CN bonds which are, in fact, vinylogous forma-mide or amidine connections in keeping with the resonance formulae, different methyl shift values are observed for some N,N-dimethylamine groups. Moreover, one-bond carbon-proton coupling constants decrease from the end to the center of the polymethine chain. This is explained by CNDO/2 calculations, in which corrected bond orders and bond angles alternating between 125° (a, y, e) and 117.5° (/5, 5) are taken into account [343],... 

The C—H coupling constants of the cyclopropyl methine carbons are also linearly correlated with the electron demand of the aryl substituents and, in addition, to the dihedral angle between the C—H orbital and the vacant p-orbital, as expressed by the equation AJ= (1 + 0.6 ff+)(10.9 -14.3 cos2 0), where ATis the difference in coupling constant between the cation and the neutral model compounds such as carbonyls. The dependence of the J values on the nature of the substituents is illustrated by the J values of 174, 177, 179 and 183 Hz for the Cl —H bond of 1-arylcyclopropylethyl cation for the para substituents OMe, Me, H and CF3, respectively59. 

Vicinal Carbon-Proton Coupling Constants for Different Dihedral Angles of C—O—C—H Arrays of Bonded Atoms, Measured from Spectra of Rigid Compounds in Natural Abundance... 

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