A quantitative study of the relationship between structure and basic frequency shifts of the 2, 4-dinitrophenylhydrazones of substituted acetophenones

Abstract

The ultraviolet and visible spectra of eleven α-substituted acetophenone 2,4-dinitrophenylhydrazones (DNP's) and twelve α, (m or p)-distributed acetophenone DNP's in chloroform and in ethanolic sodium hydroxide solution have been obtained. The difference in the absorption frequencies of these solutions, V (superscript CHCl₃) max. -V (superscript NaOH)., for the α-substituted DNP's were related to Taft's substituent constants (σ*'s) by the equation, ΔV=4,623 + 726.3 σ*, with a correlation coefficient r of 0.9527 and a standard deviation s of 124.4. ΔV has the dimension of cm�¹. A multiple regression analysis of the frequency differences for the distributed DNP's with Hammett's σ-values and Taft's σ*-values gives the equation, ΔV=4,507 + 2,462 σ + 473.4 σ*, where R= 0.9964 and s=90.9. Multiple regression analysis of the pooled data for eleven α-substituted, eight m- or p-substituted, and twelve α, (m or p)- disubstituted acetophenone DNP's gives the equation, ΔV=4,620 + 2,333σ + 521.5σ*, where R=0.9862 and s=166.4. The anti-isomers have a much larger frequency difference than the corresponding syn-isomers. Consequently, the equation immediately above serves as a criterion for distinguishing between the syn- and anti- forms of the DNP's of substituted acetophenones. The results indicate that the effects of m- and/or p-substituents on the spectra of acetophenone DNP's are essentially independent of the effects of α-substituents.