Application of Dipole Measurement in Determining Molecular Structure

The moment of the whole molecule may be obtained by vectorial addition of the group moments, taking into account magnitude, direction and sign. The result is that molecules which contain several polar groups may be non-polar as a whole, if there is internal compensation between the various polar components. Thus, we know from experience that methane and carbon tetrachloride, for example, are actually non-polar, whereas Table 13 indicates that both the C—H bond and the C—Cl bond possess a moment. 

The dipole method has proved particularly useful, apart from valence angle determination, in investigating cis- rans-isomerism, because it allows of a simple and satisfactory differentiation between the various modifications. As shown in Table 15, the moments of the rans-dihalogenated ethylenes are practically always nil, while the ctVeompounds are definitely polar. Similar conditions hold for other isomerisms of analogous nature. 

The dipole method has afforded valuable evidence also on the structure of simple aromatic parent substances. Benzene, diphenyl, naphthalene and higher condensed ring systems are recognized as plane structures. 

Symmetrically substituted methane derivatives prove non-polar and therefore tetrahedral compounds of quadrivalent tin and quadrivalent titanium exhibit the same symmetry. 

A Few Dipole Moments of p-Substituted Benzene Derivatives According to 

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