Effect of the Basic Strength of Attached Groups on Lrght Absorption Spectra II : Near Ultraviolet Absorption Spectra of Para-substituted Aniline Derivatives
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概要
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The absorption spectra of para-substituted aniline derivatives of the type of A_iC_6H_4B, where A_i is one of the electron donating groups such as NH_2, NHCH_3, NHC_2H_5, N(CH_3)_2, N(C_2H_5)_2 etc. and B is one of the electron attracting groups such as COOH, COCH_3, CHO, N0_2 etc., change with the basic strength of the group A_i. The first absorption maxima of these molecules between 2800 and 4000 A are originated from the second absorption maxima of unsubstituted molecules (in 2600〜2900 A region) under the influence of the group A_i. This is explained by semiempirical MO theory with perturbation. The effects of B groups are taken into consideration by the delocalization of the molecular orbitals of benzene molecule, while the effects of A_i groups are calculated through the method of electron migration, in which the non-bonding π electrons on the nitrogen atom of A_i migrate to the parent molecule. The induction effect of the substituted alkyl group in A_i, which determines the degree of the electron migration, can be estimated from the relative basic strength of the end group, i.e. dissociation constant of amine NHR_2. The calculated absorption energies are in good agreement with the observed values if we take the solvent effect into consideration.
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- 1957-07-05