Solvent and Substituent Effects. Concerning the Baker-Nathan Effect and the Influence of Solvent on the Principal Ultraviolet Spectral Band of Some p-Alkylnitrobenzenes and p-Alkylacetophenones¹

Abstract

The ''principal" band in the ultraviolet spectrum (due to excitation to a dipolar state) has been measured for nitrobenzene and acetophenone and their para methyl, ethyl, isopropyl and ¿-butyl derivatives in the gas phase and in a wide variety of solvents. The gas phase excitation energies are in the inductive order, with the alkyl groups responding in linear proportion to the change in electron demand in proceeding from the acetophenone to the nitrobenzene series. The effect of solvent, particularly basic solvents, is to tend to invert the order of excitation energies. Quantitative treatment of the data indicates that this effect is consistent with the operation of steric hindrance to solvation.

Trends in combating fake news on social media – a survey

“…Recently, Facebook has announced the combination of an expert-crowdsource approach in fighting the proliferation of fake news on its network. The expert-based has often been accused of being politically biased, not independent and very slow in detecting fake news (Vedova et al, 1957). While a study by Pennycook and Rand (2019) allude that the crowd is limited in many areas since they are composed of laypeople and at such, they will give the wrong prediction to content which they are unfamiliar with.…”

Light Absorption Studies: Part Xi Electronic Absorption Spectra of Nitrobenzenes

“…The ultraviolet absorptioii spectra of nitl-obenzeiie in different solvei~ts are listed in Table I. A broad symmetrical absorption band, structureless even in tlie gas phase ( 3 ) , occurs near 260 mp, which is classified as the B-band, by analogy with the B-band near 240 mp i~i acetophenones. The bands are of comparable intensity and undergo parallel changes on alteration of the dielectric constant or polarity of the solvei~t.…”

“…The spectra of nitrobenzenes have recently been describecl by a number of workers (for example, 1,2,3,4,5 ) , and the spectra have been noted to cause anomalous effects (6, 7; cf. also the greater ethylenic stretching frequency a t 1600 cm-I in nitrobenzenes ( 8 a ) , and the absence of tlie usual correlations for C-H bending vibrations in the region 1000-650 c~n-I (86)).…”

Light Absorption Studies: Part Xii. Ultraviolet Absorption Spectra of Benzaldehydes

“…Again in all other solvents, this maximum was found to be symmetrical and the shoulder was absent. For nitrobenzenes, the B-band is structureless, even in the gas phase, and quite sy~nmetrical about the maximum (13). i l l 1 explanatioll involving hydrogen bonding cannot perhaps be ruled out completely, a t least a t this stage (cf.…”