Solvatochromic shifts for some 4-nitroani- line and 4-nitrophenol derivatives as measures of relative solvent proton affinities

Abstract

Enhanced red shifts ( -AAvmux) of the [ +R2N==Cr-*-C4=NC>2-] band in the ultraviolet spectrum for 4-nitroaniline relative to A,V-diethyl-4-nitroaniline on going from cyclohexane to oxygen-base solvents are attributable primarily to the bathochromic influence of hydrogen bonding by 4-nitroaniline to these solvents and are considered to be measures of relative solvent-proton affinity. Such AA¡/max values show good correlation with * values of R in a series of ROH solvents which includes water. Good correlations between -AAvmax and * values are also obtained from the following pairs: Ar-ethyl-4-nitroaniline/iV,Ar-diethyl-4-nitroaniline and 4-nitrophenol/4nitroanisole. These probes of relative solvent-proton affinity do not, however, show ethers to be better hydrogen-bond acceptors than alcohols, probably because of steric factors.

Solvatochromism in Pure Solvents: Effects of the Molecular Structure of the Probe

“…For example, the "dielectric" or "non-specific" solute-solvent interactions are the sum of dipole-dipole, solute polarizability-solvent dipole, solute dipole-solvent polarizability and polarizability-polarizability interactions. I), followed by reference number): 1 [20]; 2 to 4 (present work); 5 [21]; 6 [22]; 7 [23]; 8 [24]; 9 [25]; 10 [26]; 11 [27]; 12 [16b]; 13 to 16 [28]; 17 [29]; 18 [30]; 19 [31]; 20 [32] and 21 to 26 [33]. ") iv) -A corollary to (iii) is as follows: for a group of probes, each tested in a series of solvents, it should be possible, in principle, to correlate the multiple regression coefficients of Eq.…”

“…3A, its inclusion, however lowers r only slightly, to 0.961; (ii) It is possible to explain the fit of probes 12 and 13 to the line of Fig. Compound 13 differs from compounds 14 to 16 in that its amine nitrogen is near-sp3 hybridized, this affects its 1s I value, as shown in Table 2 [28]; (iii) They quality of fit of the data is quite satisfactory in view of: uncertainties in pg calculated by the PM 3 method (see footnote (e) of Table 2); the dipole-dipole energy term of Eq. Compound 13 differs from compounds 14 to 16 in that its amine nitrogen is near-sp3 hybridized, this affects its 1s I value, as shown in Table 2 [28]; (iii) They quality of fit of the data is quite satisfactory in view of: uncertainties in pg calculated by the PM 3 method (see footnote (e) of Table 2); the dipole-dipole energy term of Eq.…”

“…The latter values were taken from the following references (probe number in Table 2, followed by reference number): 1 [24]; 2 to 4 (this work); 5 [34]; 8 [24]; 11 [35]; 13 to 16 [28]; 17 [36]; 18 to 20 [35]; 21 to 24 [37]. We calculated pKa values of the remaining probes, based on the fact that the effect of substituents on pK, is additive, provided that there are no complicating steric interactions, e.g., ortho effect [38], as shown in the following examples: the structural difference between probes (l), pKa = 8.6, and (6) is the presence of a carboxylate substituent.…”

Photophysical characterization and fluorescence cell imaging applications of 4-N-substituted benzothiadiazoles

“…Blue-shifted λ Amax of aromatic amines in polar protic solvents are commonly ascribed to hydrogen bonding interactions between the nitrogen lone pair and solvent protons. 24–26 Primary and secondary amines are capable of acting as hydrogen bond donors (in addition to their hydrogen bond acceptor ability) which leads to an inverse effect ( i.e. , red-shift) on λ Amax .…”

“…Blue-shied l Amax of aromatic amines in polar protic solvents are commonly ascribed to hydrogen bonding interactions between the nitrogen lone pair and solvent protons. [24][25][26] Primary and secondary amines are capable of acting as hydrogen bond donors (in addition to their hydrogen bond acceptor ability) which leads to an inverse effect (i.e., red-shi) on l Amax . Therefore, primary and secondary amines 1, 2, 11, 12, 14, and 15 displayed red-shied l Amax , whereas tertiary amines 3 and 6-9 featured blue-shied l Amax in water compared to hexane (for correlations with hydrogen bond energy see ESI, Fig.…”