Spectral property

References relevant to the spectral analyses of naturally occurring pavine and isopavine bases are presented in Tables XIII and XIV. An exhaustive numerical compilation of spectral data of these alkaloids may also be consulted (77). 

A base peak corresponding to a 6,7 (or 7,8)-disubstituted isoquinolinium ion is the prime criterion in considering a pavine or an isopavine structure. In the case of a pavine, the presence of the expected peaks may only confirm the structure deduced by other spectral and chemical means. In isopavines, however, mass spectroscopy is an exceptionally powerful tool in differentiating this group from the pavine alkaloids, as well as from other related isoquinoline bases. 

Pavines which have nonidentical substituents on rings A and D furnish two different isoquinolinium ions through the same fragmentation mode, as ex- 

References for Spectral Properties of Naturally Occurring Pavine Alkaloids 

Many of the papers dealing with the synthesis and reactions of Reissert compounds routinely include spectral data. These data are consistent with the structures assigned and with previously reported spectral data for Reissert compounds. It should be noted that comparisons of data of this type was used to assign the structures 4 and 5, which were assigned to the Reissert compounds from 1,7- ° and 1,6-naphthyridine. A detailed spectral study of Reissert salts led to the assignment of structure 19. 

The mass spectra of Reissert compounds derived from quinoline, isoquinoline, and phthalazine have been discussed. The initial fragmentation involves loss of the N substituent. Additional mass spectral data have also appeared.  

Proton magnetic resonance spectra of Reissert compounds have been studied. ° Particular emphasis has been given to the stereochemistry in these studies, and some tentative assignment of predominant tautomers has been made. 

One of the most important applications of correlation diagrams concerns the interpretation of the spectral properties of transition-metal complexes. The visible and near ultra-violet spectra of transition-metal completes can generally be assigned to transitions from the ground state to the excited states of the metal ion (mainly d-d transitions). There are two selection rules for these transitions the spin selection rule and the Laporte rule. 

The spin selection rule states that no transition can occur between states of different multiplicity i,e. AS = 0. Transitions which violate this rule are generally so weak that they can usually be ignored. 

The Laporte rule states that transitions between states of the same parity, u or g, are forbidden i.e. u - g and g - u but g +- g and u +- u. This rule follows from the symmetry of the environment and the invoking of the Bom-Oppenheimer approximation, But since, due to vibrations, the environment will not always be strictly symmetrical, these forbidden transitions will in fact occur, though rather weakly (oscillator strengths of the order of 10 4). All the states of a transition-metal ion in an octahedral environment are g states, so that it will be these weak symmetry forbidden transitions (called d-d transitions) that will be of most interest to us when we study the spectra of octahedral complexes. 

By consulting the appropriate correlation diagram, it is possible to see what kind of d-d spectrum a transition-metal ion in a given environment should have. For qualitative predictions we can use diagrams of 

V + salt also shows some very weak bands (/ 10 7) in the 20 000- 

To conclude this survey of those properties of the water molecule which will be important in our later discussion, we give a brief review of the transitions which can occur between the different energy states of the molecule and the spectral absorptions which are associated with them. 

In the visible region of the spectrum water vapour is transparent and all further absorptions of interest occur in the infrared or at even longer wavelengths. These are associated with transitions between vibrational levels of the molecule, the fundamental modes for which are shown in fig. 1.4, and have a fine structure dependent upon the rotational levels involved. Since each of the three normal modes has a direct effect upon the dipole moment of the molecule, they aU lead to absorption bands. Because the interatomic potentials have appreciable anharmonic components from terms of cubic or higher order in the displacements, the relation between 

The bands which are of particular interest are those which lie in the near-infrared region and which can be fairly easily related to particular vibrational transitions, for the changes in these bands when the molecules are closely interacting in a liquid or solid phase 

Within each absorption band the absorption is not continuous but has the form of a series of closely spaced lines representing transitions between different rotational levels of the molecule. Because the molecule HgO is an asymmetric top, in the classical sense, meaning that its three principal moments of inertia are all unequal, the line spacing is very irregular. Several bands have, however, been analysed (Herzberg, 1945, pp. 484-9) and from them the principal moments of inertia and hence the geometry of 

In the lowest vibrational state of the molecule the values are slightly different  

The ultraviolet absorption spectra of l,2,4-triazolo[4,3-a]pyrimidines have been studied. Amide-imidic add tautomerism in l,2,4-triazolo[4,3-ajpyrimidinones has also been studied using this tool [59JOC779 77HC(30)179], The spectra of the 5-oxo-l,2,4-triazolo[4,3-a]pyrimidines (158) exhibited three absorption bands at -230,260, and 310 nm (87T2497). The 7-oxo congeners (18), in contrast, revealed only one band at 230 nm (87T2497). 

As a rule, the order of chemical shifts of the methine protons of 1,2,4-triazolo[4,3-a]pyrimidines was found to be 8 (ppm) H3 H5 H7 H6 (77AJC2515 83S44). 

The order of chemical shifts for the carbons of l,2,4-triazolo[4,3-a]py-rimidines was found to vary according to the type and positions of substituents attached to their skeleton (75JHC1187 83S44 89H(28)239 94MI1 95JCS(P1)2907]. 

The mass spectra of l,2,4-triazolo[4,3-a]pyrimidines showed, mainly, their molecular ion peaks [83S44 88JCS(P1)351 94LA1005]. The mass spectra of l,8a-dihydro-l,3,7-trisubstituted-l,2,4-triazolo[4,3-a]pyrimidines 41 revealed a common peak of the nitrileimine 159 (94LA1005). 

Extensive studies have been reported on infrared vibrational frequency correlations of isatin and a variety of substituted isatin.79,167,224-226 Infrared evidence supports structure 1 for isatin and gives no evidence for the lactim or enol form.225,229 In contrast to isatin infrared studies indicate that the so-called 4,5, ( , 7-tetrahydroisatins exist as the enol tautomer 19.79 

In concentrated solution 7-methylisatin-4-carboxvlic acid exhibits normal carboxylic acid dimerization, but in the solid state the lactol form 58 is present.228 Infrared studies indicate that hydrogen bonding as shown in 59 best represents the structure and mode of association of 

A number of studies of the ultraviolet absorption spectra of isatins have appeared.34,232-235 The absorption curves of isatin and A -methyl-isatin are practically identical.233 

Kurosaki, Nippon Kagaku Zasshi 82, 1555 (1961) Chem. Abstr. 58, 12088 (1963). 

Isatin has been reported to fragment predominantly by successive loss of CO, HCN, and CO from the molecular ion on electron impact, and also by consecutive loss of two molecules of CO from the molecular ion followed by loss of HCN.236 Use of 3-13C-labeled isatin shows that the initial loss of CO occurs entirely from the 2-position.237 Mass spectral studies have also been carried out on a variety of derivatives of isatin.236-241 

If a benzenoid hydrocarbon is represented by a molecular graph G in the usual manner [3, 21,24] and if the vertices of G are labeled by 1, 2,. .., n (in an arbitrary order), then the adjacency matrix A of the graph G is defined via its matrix elements as 

The eigenvalues of A will be denoted by xt, x2. xn. They form the spectrum of the graph G. 

The characteristic polynomial of G is just the characteristic polynomial of the adjacency matrix. It will be denoted by cp(G). Then 

The spectral theory of graphs is well elaborated, both in the case of general graphs [25] and graphs of interest in chemistry [24]. In this section we are concerned with the graph spectra which are specific for benzenoid systems. 

One such regularity has already been mentioned, namely the Dewar — Longuet-Higgins formula, Eq. (1). Bearing in mind Eqs. (2) and (3) as well as the pairing theorem 

1° amine, two N—H stretching bands 2° amine, one N—H stretching band 3° amine, no N—H stretching band. 

The longest-wavelength absorption bands in the electronic spectra of strained [n]para- and [njmetacyclophanes and their condensed benzenoid analogues are summarized in Table 4 together with their reference compounds. It can be seen that, as the length of the bridge n decreases, the [n]cyclophanes exhibit remarkable bathochromic shift. This is mainly due to decrease of the HOMO/LUMO gap as a result of destabilization of the former and stabilization of the latter. 

Thorough assignment of the NMR signals of [6]paracyclophane derivative Ig (Structures 2) was undertaken by Tochtermann and Gunther by means of the 2D NMR techniques [52]. The NMR spectra of [6]paracyclophanes exhibit 

8) was determined by means of quadrupolar deuterium coupling at very high field [59]. The susceptibility of 4e is similar (or even lower than) to that of appropriate reference compounds, indicating that the [5]paracyclophane system is fully aromatic in spite of its highly deformed geometry of the benzene ring. 

Refractive indices of plasticizer and polymer are behind brilliance. The closer are both indices to each other the better the brilliance. Usually this is achieved by selection of the plasticizer of high refractive index. It should be noted that refractive index is not the only determinant. An incompatibility or tendency for the plasticizer to crystalhze offsets gains due to the refractive index match. 

Spectral properties of plasticizers are useful in various studies, especially in helping to understand various aspects of the mechanism of plasticizer action. Table 10.1 shows typical IR absorption peaks by representatives of major groups of plasticizers. 

The data in Table 10.2 show that it is possible to identify the plasticizer based on results of NMR measurements. A mass spectral guide is available for a quick identification of diall l phthalates using GC-MS analysis.  

DPP R Shade Absorption maxima (nm) in solution in solid state max max 

As with many other classes of pigments, all DPP pigments show a bathochro-mic shift of the maximum absorption in the solid state with respect to the maximum absorption in solution. The soUd-state absorption maxima of DPP depends strongly on the nature and position of the substituent. In comparison with the unsubstituted DPP 2, the of m,m substituted DPP often show a hypsochro-mic shift and the X ofp,p substituted DPP a bathochromic shift. 

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It should be emphasized that isomerization is by no means the only process involving chemical reactions in which spectroscopy plays a key role as an experimental probe. A very exciting topic of recent interest is the observation and computation [73, 74] of the spectral properties of the transition state [6]—catching a molecule in the act as it passes the point of no return from reactants to products. Furthennore, it has been discovered from spectroscopic observation [75] that molecules can have motions that are stable for long times even above the barrier to reaction. 

Quin L D and Verkade J G (eds) 1994 Phosphorus-31 NMR Spectral Properties in Compound Characterization and Structural Analysis (New York VCH)... 

Multivariate data analysis usually starts with generating a set of spectra and the corresponding chemical structures as a result of a spectrum similarity search in a spectrum database. The peak data are transformed into a set of spectral features and the chemical structures are encoded into molecular descriptors [80]. A spectral feature is a property that can be automatically computed from a mass spectrum. Typical spectral features are the peak intensity at a particular mass/charge value, or logarithmic intensity ratios. The goal of transformation of peak data into spectral features is to obtain descriptors of spectral properties that are more suitable than the original peak list data. 

The physical properties of the xanthene type dye stmcture in general have been considered. For example, the aggregation phenomena of xanthene dyes has been reviewed (3), as has then photochemistry (4), electron transfer (5), triplet absorption spectra (6), and photodegradation (7). For the fluoresceins in particular, spectral properties and photochemistry have been reviewed (8), and the photochemistry of rhodamines has been investigated (9). 

Gallium [7440-55-3] atomic number 31, was discovered through a study of its spectral properties in 1875 by P. E. Lecoq de Boisbaudran and named from Gallia in honor of its discoverer s homeland. The first element to be discovered after the pubHcation of Mendeleev s Periodic Table, its discovery constituted a confirmation of the Table which was reinforced shordy after by the discoveries of scandium and germanium. 

The emissivity, S, is the ratio of the radiant emittance of a body to that of a blackbody at the same temperature. Kirchhoff s law requires that a = e for aH bodies at thermal equHibrium. For a blackbody, a = e = 1. Near room temperature, most clean metals have emissivities below 0.1, and most nonmetals have emissivities above 0.9. This description is of the spectraHy integrated (or total) absorptivity, reflectivity, transmissivity, and emissivity. These terms can also be defined as spectral properties, functions of wavelength or wavenumber, and the relations hold for the spectral properties as weH (71,74—76). 

These spectral properties give rise to the wide range of appHcations of PMDs as silver haHde sensitizers (11), laser media components (12,13), polymerization initiators (14), etc. 

The hterature on polymethine dyes has been reviewed (3,4,7,9—11,21). Reference 3 is the best among recent (1995) sources on the chemistry and spectral properties of this dye class it also contains a large bibhography. 

There are two main kinds of dye aggregates, characterized by their typical spectral properties J-aggregates and H-aggregates. The absorption band maximum (f-band) of the J-aggregates is shifted bathochromicaHy with respect to that of an isolated molecule (M-band) the absorption maximum of the H-aggregates is shifted hypsochromicaHy (H-band). The dyes can also form dimers with a shorter absorption wavelength (D-band). 

The synthesis of these compounds is shown in Figure 5. Extensive compilations of the chemical, and chromatographic and spectral properties of compounds (10) and (12) are given in References 43 and 44, respectively. 

Vitamin K compounds ate yellow solids or viscous liquids. The natural form of vitamin is a single diastereoisomer with 2 (E), 7 (R), ll (R) stereochemistry. The predominant commercial form of vitamin is the racemate and a 2 (E)j (Z) mixture. Table 1 fists some physical and spectral properties of vitamin K. ... 

There have been approximately 60 references to thiazine dyes in the past 15 years of Chemical Jibstracts. Although most of these references are to titration indicators, photophysical evaluation, and spectral properties, a few refer to stmctures for use as dyes (13). 

There is no easy understanding of the spectral properties of these compounds in general, which may or may not have a built-in chromophoric system responsible for a long-wavelength absorption like 7,8-dihydropteridin-4-one or a blue-shifted excitation like its 5,6-dihydro isomer. More important than the simple dihydropteridine model substances are the dihydropterins and dihydrolumazines, which are naturally occurring pteridine derivatives and reactive intermediates in redox reactions. 

The NMR spectral properties of the parent heterocycles are summarized in Table 12. The signal for the pyrrole a-carbon is broadened as a result of coupling with the adjacent nitrogen-14 atom (c/. Section 3.01.4.3). While the frequencies observed for the /3-carbon atoms show a fairly systematic upheld shift with increasing electronegativity of the heteroatom, the shifts for the a-carbon atoms vary irregularly. The shifts are comparable with that for benzene, S 128.7. 

Infrared, electronic and mass spectral properties of azetidines are discussed in Sections 5.01.1.4-5.01.1.6. 

The product exhibits the following spectral properties IR (CHCI3)... 

A variable pressure oil pump was used in this distillation. Approximately 10 g of a volatile component, consisting mostly of hexamethyl-disiloxane, was obtained at room temperature (15 (in) before the forerun. The forerun contained the desired product and mineral oil from the n-butyllithium solution. The pot residue was about 5 g. The submitters find the disilyl compound thus obtained is contaminated with a trace amount of mineral oil and 4-6% of a vinylsilane, probably 2-methyl-l-trimethylsiloxy-3-trimethylsilyl-2-propene. This impurity becomes quite significant if the reaction medium is less polar than the one described (e.g., too much hexane from n-butyllithium is allowed to remain behind). The spectral properties of the desired product... 

The product showed the following spectral properties H-NMR (CDCI3)... 

Gas chromatographic analysis of the product on a 1-m column packed with 20% Silicone SE-30 at 180°C should give a single peak. The product has the fallowing spectral properties IR (film) cm" 1710, 1630 (C=C) ... 

The following spectral properties were recorded for 3-butyroyl-l-... 

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