Hypsochromic shift

The auto-association of A-4-thiazoline-2-thione is clearly indicated b the hypsOchromic shift (5 nm) of the 315-nm band when the spectrum is first recorded at 50°C and then at —25°C (10 M in cyclohexane). In the same temperature range the spectrum of 3-methyl-A-4-thiazoline-2-thione remains unchanged (61).  [c.381]

A hypsochromic shift of 20-50 cm is observed in the double-bond stretching region, when the enamines are converted to the corresponding iminium salts by the electrophilic addition of a proton at the /3-carbon atom. The shift is accompanied by an enhancement in the intensity of the band. Leonard and co-workers (68,71-74) have used this absorption shift as a diagnostic tool for the determination of the position of the double bond  [c.39]

He found that the UV maximum exhibits a hypsochromic shift in an alkaline medium. In the IR spectra he found maxima in the carbonyl  [c.236]

Addition of a proton to a nitrogen-containing heteroaromatic base usually produces only a small shift (about 5 m/Lt) in the wavelengths of the absorption maxima. Somewhat greater effects can be produced if either the neutral base or its cation has a significant resonance stabilization that is lacking in the other, or if the band is due to an n-TT transition (leading to a hypsochromic shift on cation formation). Some systems where no such explanation is apparent nevertheless show large spectral changes in passing from the neutral molecule to the cation, and the observation of anomalous shifts of this kind in the  [c.45]

Electron-donating or -withdrawing properties of a substituent on the 4 and 5 positions have also been used in order to modulate the basicity in the hope to observe either hypsochromic or bathochromic shift (110).  [c.76]

The most conspicuous physical feature of the retinoids and of the carotenoids is the uv spectmm. In the case of the carotenoids, this coloration property is one reason for their commercial significance. In general, there are several factors which influence the position of the intensity of the absorbance, and the degree of fine stmcture (13). These include the length of the polyene chain, the number of cis double bonds, and end group functionahty. For example, aH-Zra/ j -retinal (5) has an absorption maximum at 368 nm and a molecular extinction coefficient at 48,000, whereas the 7,9,11,13-cis isomer has values of 308 nm and 15,500. Both hypsochromic shifts and hypochromic effects are observed when the stereochemistry of the double bond is changed from trans to cis. External factors such as solvent, temperature, and molecular environments also influence the uv spectra. A striking example of the latter phenomenon is the observed significant bathochromic shift (ca 150 nm) during the association of a carotenoid with a hpoprotein. From a molecular standpoint, the origins of this effect are not completely understood and this remains an area of active research (14,15).  [c.97]

Dimroth et al. introduced 8 as a solvatochromic probe of solvent polarity having absorption in the visible region it shows the largest solvatochromic shift of any substance yet reported. Ey (30) is calculated with Eq. (8-76), like Z. (The peculiar symbolism arose because compound 8 happened to be No. 30 on the list of substances studied by Dimroth et al.) The shift is hypsochromic as solvent polarity is increased. Table 8-16 gives some Ey (30) values. - (30) is linearly  [c.437]

The 5-acylamino-THISs are devoid of carbonyl absorptions above 1600 cm ), suggesting that their oxygen atom adopt a considerable part of the negative charge of the system (6). A normal carbonyl band appears on protonation, also accompanied by a hypsochromic shift in ultraviolet absorption (6). H-4 of 5-acyl-amino-THISs resonates near 7.4 ppm in the H NMR spectrum (6). Three fragmentation modes of the molecular ion of these mesoioiis have been observed (6) rupture of the 2,3 and 1,5 bonds with formation of an R CS" ion, rupture of 1,2 and 3,4 bonds with formation of R CNR, and cleavage of the 2,3 and 4,5 bonds giving rise to R NCR -.  [c.14]

Nishimoto s fractional core charge model introduced in the Pariser-Parr-Pople method allows good correlation between experimental data, calculated characteristics of electronic absorption of thiazolium salts, and oxidation and reduction potentials (15). Quaternization of the nitrogen atom of a thiazole molecule gives a shift of the first band (662, 663). The importance of the bathochromic effect produced by a methyl substituent in different positions of the nucleus depends on the position of the methyl group as shown by the comparison of theoretical increments (in brackets) to the measured ones (Scheme 10) (15). The important hypsochromic shift [4.92 eV (252 nm) to 5.44 eV (229nm)] observed between absorption of 4-phenylthiazole and 2,3-dimethyl-4-phenyl-thiazolium has been related to the absence of conjugation between the two cycles as the methyl group on the nitrogen atom prevents the phenyl ring from being coplanar with the thiazole (15, 660).  [c.31]

The meso carbon atom should present a carbenium structure with a low TT electron density in the ground state, in the excited state this carbon possesses the carbeniate structure (C ) with a high tt electron density (119). An electron-donating group in such a position should stabilize the ground state and rise the excited state to the highest level hypsochromic shift results as a whole.  [c.77]

The shade may be varied by choosing amines. For aromatic amines, the steric effect of substituents in the ortho position reduces the conjugation of the anibno group with the anthraquinone moiety, and the result is a hypsochromic shift and brighter shade. Thus Cl Acid Blue 129 (120) has a more reddish and brighter shade than Cl Acid Blue 25 (118). Cycloalkylamines have a similat effect on the shade. Cl Acid Blue 62 [5617-28-7] (125) Cl 62045) is an example.  [c.324]

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  [c.273]

Hypoxanthine, 2-trifluoromethyl-synthesis, 5, 587 Hypoxanthine, trimethylsilyl-glycosylation, 5, 536 Hypoxanthinium nitrate, 1,3,7-trimethyl-thiation, 5, 540 Hypsochromic shift, 1, 344  [c.647]

If other groups capable of conjugation are adjacent to the enamine grouping they can also participate in the salt formation. Thus for example, /3-amino- ,/3-unsaturated ketones can undergo protonation on the carbonyl oxygen atom as well as possible protonation at the carbon and nitrogen atoms. Salts of -octahydro-7-quinolone (64) have their proton situated on the oxygen atom (100) 168). The evidence for this structural assignment comes mainly from the hypsochromic shift in the ultraviolet absorption spectrum [the free base exhibits A a, 298 m/x (log 4.53) and the salt A, ax 280 m/x (log 4.30)]. Salts of tertiary enamino ketone 101 are formed in a similar manner.  [c.276]

In the UV spectrum of the protonation products there is a hypsochromic shift of the absorption maximum of enyne system compared to the bases (74DIS) this agrees with the data of the protonation of simple enamines and dienic amines (69MI1).  [c.192]

Knott s rule concerns the importance of the place of the nitrogen atom replacing a methine carbon in the conjugated chain when the atom is separated from the active auxochromic atoms by an odd number of conjugated atoms, the shift is bathochromic. It is hypsochromic when there is an even number, Tne importance of the shift could establish a measure of M effect of various heterocyclic nuclei (79. 124). Many papers have been published, and examples have been given to verify these rules (79-84).  [c.78]

Incorporation of substituents into aromatic systems which are electron donating, eg, hydroxy, methoxy, amino, alkylamino, dialkylamino, etc, tend to shift light absorption to longer wavelengths (bathochromic shifts). Such groups are known as auxochromes, from the Greek auxo meaning increase. They are auxiUaries to the chromophores and enhance and modify absorption and color by vktue of thek nonbonding electrons. Groups that withdraw electrons have the opposite effect, making electron excitation less facile, and consequendy shift absorption to shorter wavelengths (hypsochromic shifts).  [c.22]

See pages that mention the term Hypsochromic shift : [c.76]    [c.77]    [c.65]    [c.276]    [c.647]    [c.435]    [c.436]    [c.157]    [c.255]    [c.285]    [c.45]    [c.45]    [c.139]    [c.112]    [c.12]    [c.151]   
Chemical kinetics the study of reaction rates in solution (1990) -- [ c.435 ]