Basicity band shift

AVg(basicity) = relative shift in the OD band maximum in the IR spectra of CH3OD in benzene and the proton accepting solvent used as solute in reverse osmosis, cm l... 

The visible absorption bands of a series of azobenzene complexes are reported in Table 13. It has been noted that the visible band shifts to higher energy on increasing the a basicity of the coligand L.208... 

Infrared spectra also show a minor alteration of aldrin on the basic alumina column as evidenced by a shift of the 720 cm. 1 band to 710 cm."1 The same shift occurs when aldrin is chromatographed on acid or on neutral alumina. This band shift is more pronounced at lower concentrations, while at higher concentrations both the 720 cm."1 and the 710 cm."1 bands are observed. 

At present the basic red shift and the accompanying solvent effects have been extensively investigated only as far as the lowest 1B+ state of PRSB is concerned. Theoretical calculations predict a decrease in the energy of the "cis" - -Aj state upon protonation which is smaller (121) or comparable (126) to that of the - -bJ state. The latter prediction seems to be consistent with the 340-nm location of band II for PRSB in solution (127,128). 

Optical Spectra. The main (a) band in a variety of visual pigments exhibits absorption maxima in the range between 430 and 580 nm. It is this variability, as well as the basic bathochromic shift relative to a free PRSB in solution, which have provided the basis for most of the spectroscopic theories relevant to the structure of the chromophore and its environment in the binding site. Attempts to rationalize the shift in terms of charge-transfer complex formation between the (unprotonated) Schiff base and a protein functional group (200,210,212,228) have never... 

Such interactions are presumed to induce and control electron delocalization in the it system. As a commonly accepted principle in polyene spectroscopy (6,60,243), delocalization induces a basic bathochromic shift in the absorption maximum of the main (1B+) band. The magnitude of the shift in each pigment is controlled by specific electrostatic effects in the binding site. 

In a similar way, another set of solvent Lewis-basicity parameters, i phOH) based on band shifts of the O—H stretching vibration of phenol in tetrachloromethane induced by hydrogen-bond formation with added HBA solvents B, was used by Koppel and Paju [88] to classify 198 solvents, according to Eq. (7-36) (5phOH = 0 for CCI4) ... 

Different charge-compensating cations in zeolite L have been tested for their promotional effect in n-hexane aromatization. Apparently, high basicity of the alkaline and alkaline earth promoter favors n-hexane aromatization. Basicity and selectivity both increase from Li and Cs 331) and from Mg to Ba (22,25). Bezouhanova et al. studied the FTIR bands of linearly adsorbed CO in the range of 2060-2075 cm . One band at 2075 cm", which is also found on unsupported Pt, is attributed to extrazeolite Pt particles, a second band shifts from 2060 cm" for Li to lower wavenumbers with K and Rb 331). Another criterion, used by Larsen and Haller, is the measured rate of competitive hydrogenation of benzene and toluene, which has been found to correlate with the zeolite basicity (25). As described in a previous section, this method had previously been used by Tri el al. to probe for the electron deficiency of Pt particles in acidic zeolites 332). The rate data are analyzed in terms of a Langmuir-Hinshelwood model and the ratio of the adsorption coefficients of toluene and benzene, A, /b, is determined. It was found to decrease from 8.6 for Pt/Si02, and 5.4 for Pt/MgL, to 4.4 for Pt/BaL. As direct electron transfer from the cations to neutral Pt particles is unlikely, an interaction of Pt with the zeolite framework or with... 

The hypothesis of Doub and Vandenbelt that the spectra of substituted benzenes can be understood as a shifting of the three basic bands of benzene seems sufficient to understand qualitatively the spectra of these lignin model compounds. Absorptions below about 260 nm are B transitions, while those above are due to and transitions. Depending on the exact substitution pattern, the band may be obscured under the more intense band. 

Other differences among this class of alkaloids resides in the type of substituent (hydroxy, methoxy, or methylenedioxy) and in the presence or absence of a methyl group at the nitrogen. They show an absorption maximum at about 283 nm in the UV spectrum, in common with many isoquinoline alkaloids. For those cularines with a phenolic group, under basic conditions, this band shifts to 294 nm. 

Basic properties of the samples were studied by FTIR spectroscopy using CDCI3 adsorption at 20 °C. At the formation of H bonds, deuterochloroform behaves as a typical acid. A decrease in the frequency of vcd band of CDCI3 adsorbed relative to the value of physisorbed molecules (2265 cm-i) is caused by the formation of complexes with base sites. The strength of base site was determined by the band shift of the CD stretching vibrations that occurred under CDCb adsorption. The strength can be recalculated into the proton affinity (PA) scale using the formula (Paukshtis, 1992) ... 

These modifications are related to the changes observed in the IR spectra. Introduction of only 0.1% Na causes the extinction of the most basic band at 3772 cm-i emd gives rise to a new, comparatively more acidic band (3755 cm-i) which grows in intensity and dominates the spectrum as the sodium content increases. The bemd of type II hydroxyls (3728 cm- ) has an opposite progression its position shifts to higher wave numbers (3734 cm ) and its intensity is gradually diminished by increasing amoimts of sodiiun until its complete extinction for 1% Na. The other bands (3677 and 3597 cm l) are affected less. 

A bathochromic shift of about 5 nm results for the 320-nm band when a methyl substituent is introduced either in the 4- or 5-posiiion, The reverse is observed when the methyl is attached to nitrogen (56). Solvent effects on this 320-nm band suggest that in the first excited state A-4-thiazoline-2-thione is less basic than in the ground state (61). Ultraviolet spectra of a large series of A-4-thiazoline-2-thiones have been reported (60. 73). 

Their physical properties closely resemble those of pterin, which has a basic pKt, of 2.20 and an acidic one of 7.86 associated with N-1 protonation and a hypsochromic shift of the long-wavelength absorption band in the UV spectrum, and N-3 deprotonation effecting a bathochromic shift respectively (Table 4). The xanthopterin (4) and isoxanthopterin types... 

In the present work low temperature adsoi ption of fluoroform and CO, were used to characterize surface basicity of silica, both pure and exposed to bases. It was found that adsorption of deuterated ammonia results in appearance of a new CH stretching vibration band of adsorbed CHF, with the position typical of strong basic sites, absent on the surface of pure silica. Low-frequency shift of mode of adsorbed CO, supports the conclusion about such basicity induced by the presence of H-bonded bases. 

In the case of substances whose structures are pH-dependent (e.g. phenols, carboxylic and sulfonic acids, amines etc.) it is possible to produce fluorescences or make them disappear by the deliberate manipulation of the pH [213] (Table 20). Shifts of the positions of the absorption and emission bands have also been reported. This is particularly to be observed in the case of modified silica gels, some of which are markedly acidic or basic in reaction (Table 25). 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

A similar effect can be observed in anthaquinones, mainly for the presence of an hydroxyl group. The ionization of hydroxyl groups under basic conditions also undergoes a bathochromic shift. Alizarin has two absorption bands in the vis region, simated at 567 and 609 nm carminic acid has a visible absorption maximum at around 500 nm and kermesic acid at 498 mn. 

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