Spectra in water

Ultraviolet spectra in water for neutral species. The spectral differences between the hydrated cations and the cations of the corresponding dihydro derivatives are of the same magnitude as those observed between the neutral species. 

Table 11 Electronic absorption spectra (in water) and electrochemical data (in CH3CN) for Ni11 complexes...

Models 1-4 have a fundamental drawback The librational absorption band calculated for water appears to be too wide. This drawback at first glance could be overcome, if one employs the so-called field models, in which the static potential presents a smooth well (where a notion of a collision of a dipole with a wall actually has no physical sense). However, from the discussion given just below we shall see that this reasonable idea does not work properly with respect to calculating the wideband spectra in water. 

Thus, the field models could not give a satisfactory description of the wideband dielectric spectra in water and in typical nonassociated liquids, since too narrow quasi-resonance and poor low-frequency spectra are characteristic of the field models. Note, field models could be successfully employed for calculation of the R-band in water, see Sections VII.B, IX, and X. 

Fig. 10 Comparison of the VA and VCD spectra of ML in water calculated using the PCM model at the three levels of theory (top three traces) with the corresponding experimental spectra in water...

The spectra of calcium and sodium lignosulfonates (Fig. 5.2.6) show similar characteristics when recorded in aqueous solutions and in KBr pellets. However, the peak intensities in the CATR spectra in water (particularly in the carbonyl stretching region, including the 1600cm-1 band) are greatly reduced. The prominent band for the lignosulfonates at 1040-1043 cm 1 (R—SOz—O- sym.)... 

Aminopyrazine is a yellowish crystalline solid with m.p. 118-120 (420). It is a weak base with reported pAj, values of 3.14 (123) and 2.96 (821) (others are recorded in Chapter X). The similarity in the ultraviolet spectra (in water) of the neutral molecules of 2-amino-, 2-methylamino-, and 2-dimethylaminopyrazines, and of their monocations, and their similar basic strengths (2.96,3.42,3.27) (821) supports the conclusion that in aqueous solution 2-aminopyrazine exists mainly in the amino form (20) (821). The ultraviolet spectrum of 2-aminopyrazine cation differs from that of the neutral molecule of pyrazine, thus indicating that protonation does not take place at the extranuclear nitrogen atom (821) 2-aminopyrazine in fact protonates at Ni (see below). 

Figure 1.39 Generic structure of tf (dipicolinato)lanthanide complexes (top) (a) plot of the Ln-N (circle) and Ln-O (triangle) distances vs lanthanide ionic radius (h) absorption spectra in water plot of the hyperpolarisability coefficient /3 vs ionic radius (c) or /-orbital filling (d)...

The substituent effect on the tautomeric equilibrium in solution has been studied using experimental pKa values and UV spectra (in water at 20 °C) of several 4(177)-pyridones and their N- and O-fixed derivatives. It was concluded that most of the factors affecting the tautomerism of 4(l/7)-pyridones are due to the electronic effect, including steric effect, of the substituents in the 2-position. Thus, the proportion of the hydroxy form increases on introduction of an electron-withdrawing group into the 2-position. For example, 5-methoxy-4(l/7)-pyridones with a methyl, hydroxymethyl, and methoxymethyl groups in the 2-position exist essentially in the pyridone form however, 2-methoxycarbonyl-substituted derivative exists as a mixture of hydroxy and oxo form in water (77BCJ710). The effect of substituents in the 3-position... 

Tautomerism of 6-iminobarbiturates 209 depends upon the substituent on the N(3) atom. NMR spectra in dipolar aprotic solvents, UV spectra in water and ethanol, IR spectra and studies at different temperatures indicate the conjugated structure 209b for 209 (R = H) and non-conjugated structure 209a for 209 (R = Me, Ph) (88CPB563). 

For a solvent such as acetonitrile that is a poor donor (D.N. = lU.l) (7.), the variable temperature CD spectra of the (S)-2-chloropropionate complex (Figure 9) can be understood in terms of the shift in the equilibrium towards the energetically preferred rotamer I at low temperature. This shift in the equilibrium is heightened by the increase in the dielectric as the temperature is lowered. The CD spectra in water and methanol also become more negative as the temperature is lowered. 

Spectral Determinations. The circular dichroism spectra were obtained on a Cary 60 modified as reported previously (20J. The spectra were obtained with aqueous solutions. The 1 1 v/v CD30D/ CD2C12 XH NMR spectra were obtained with a Perkin Elmer R-12 spectrometer. The ultraviolet/visible electronic spectra in water or chloroform were obtained with a Cary 14 spectrophotometer with matched one cm Supracil cells. 

The harmonic-vibration model of the HB molecules, described in Section VI, was first successfully applied in Sections III and IV for calculation of the permittivity spectra in water in the range 50-300 cm-1. Then it turned out that this model satisfactorily agrees with experiment also for ice. Moreover, in ice the... 

The model described in this chapter can be applied to the calculation of the permittivity spectra in water in the broad frequency range 0-1000 cm-1 and to calculation of the ice far-IR spectra in the resonance region 50-1000 cm-1. As seen in Fig. 26 (curves I), in a nonresonance ice spectrum only the transverse-vibration mechanism (d) works. Indeed, we see from Fig. 24b that at v < 50 cm-1, namely in the submillimeter wavelength region and at lower frequencies, mechanisms a-c practically vanish. 

DIFFERENTIAL ENERGY SPECTRA IN WATER 60C0 POINT ISOTROPIC SOURCE... 

FIGURE 5 SNARF-1 dextran/urease capsule fluorescence spectra in water in the presence of urea from 1 O to 0.1 M. 

The 4-hydroxy-6-methyl-2-pyridone structure (XII-483) is consistent with its NMR, ir, and uv spectra and is similar to that of 4-hydroxy-2-pyridone. Ultraviolet spectra in water and ethanol and infrared spectra (KBr) show that glutazine and several of its derivatives (XII484 R = H,CN, CONH, C02Et) exist as an equilibrium mixture of the 4-amino-6-hydroxy-2-pyridone (XII-484a) and the 4-aniino-2,6-pyridinedione (XII-484b). ... 

Figure 1 - Sonoluminescence spectra in water under transient cavitation dissolved gas Ar (a) at 20 kHz (b) at 1.7 MHz (relative intensities) ...

Figure 10 The structures of the foldamer (13) and pinene 14, and its ICD spectra in water/acetonitrile (40/60) solution. (—)-a-Pinene (yellow line, 4.2 x 10 " M), oligoma- (green line, 4.2 x 10 M) in the presence 100 equivalents of (—l-a-pinene (blue line) and (-b)-a-pinene (red line). (Reprinted with permission from Ref. 27. Cop)night 2000 American Chemical Society.)...

Figure 88. Comparison of IR absorplion spectra in water with lETS spectra when adsorbed on aluminum oxide [308], of...

Nicotinic acid and nicotinamide (Table 7.1) are eolourless erystalUne substances each is insoluble or only sparingly soluble in organie solvents. Nieo-tinic acid is slightly soluble in water and ethanol nieotinamide is very soluble in water and moderately soluble in ethanol. The two eompounds have similar absorption spectra in water, with absorption maxima at 262 nm. 

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