Molecular Structure of Allene from its Proton NMR in a Nematic Solvent

摘要

The proton NMR spectrum of allene dissolved in the nematic mesophase ofp,pprime;hyphen;dihyphen;nhyphen;hexyloxyazoxyhyphen;benzene has been obtained at 75deg;C. Computer analysis of this spectrum gives the parameters of the spin Hamiltonian. The structure of allene has been determined from the elements of the spin Hamiltonian assuming that the two CH2planes are perpendicular to each other. It is found that the ratio of the geminal Hsngbnd;H bond length to the Csngbnd;H bond length is 1.7133 and is in good agreement with the electron diffraction value of 1.7180. Again in comparison with electron diffraction, the Csngbnd;C bond length is too short relative to the Csngbnd;H bond length by 4percnt;. This shortness could not be completely explained on the basis of molecular vibrations.