Spectral Behavior

Because many of our organotin products are not very soluble, we have looked at avenues for physical characterization that do not require the material to be in solution. We have used a munber of mass spectral techniques to characterize these materials. Here we will describe for illustrative purposes some results for the product derived from the reaction of dimethyltin dichloride and norfloxacin.  

Tin contains 10 naturally occurring isotopes with 7 of them present in a reasonable abimdance to allow identification by MS. Table 3 contains isotopic ion abundance matches for selected tin-containing ion fragments. The matches are reasonable and consistent with the presence of tin in these ion fragments. 

Results for the product derived from reaction of dimethyltin dichloride and norfloxacin appear in Table 4. Only the molecular weight of the most abundant ion 

Unlike HREI MS, the particular mass spectrometry employed for the MALDl studies is not highly accmate, making isotopic abundance studies difficult. Nevertheless, some matches were made, and selected ones are included in Tables 5 and 6. Reasonable matches are the exception rather than the rule. Fmiher, results that reflect the relative isotopic abimdance are leveled as the number of units, and consequently the isotopic characteristics are lost. Thus MS is a useful tool for structural identification, including, sometimes, end groups. It also allows an insight into the thermal stability of certain groups. 

Other xiseM structural reports on the structural analysis of organotin products not given elsewhere are found in literature for fluorescence, photodegradation by UV light, size exclusion chromatography, and NMR and chro- 

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Transmission Fourier Transform Infrared Spectroscopy. The most straightforward method for the acquisition of in spectra of surface layers is standard transmission spectroscopy (35,36). This approach can only be used for samples which are partially in transparent or which can be diluted with an in transparent medium such as KBr and pressed into a transmissive pellet. The extent to which the in spectral region (typically ca 600 4000 cm ) is available for study depends on the in absorption characteristics of the soHd support material. Transmission ftir spectroscopy is most often used to study surface species on metal oxides. These soHds leave reasonably large spectral windows within which the spectral behavior of the surface species can be viewed. 

Some quinolinoquinone heterocyclic dimethine cyanine dyes have been prepared, and their solvatochromic and spectral behavior in buffer solutions has been... 

For the silica gel (Figure 3A), the solution was removed slightly less effectively, and more Cs was left (ca. 0.0020 atoms/A2). The spectral behavior is quite similar to that of boehmite, except that there is a peak due to surface Cs coordinated by only water molecules and not in contact with the surface oxygens (so-called outer sphere complexes)at 30% RH. Complete dynamical averaging among sites at frequencies greater than ca. 10 kHz occurs at 70% RH and greater. 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

The mass spectral behavior of several nuclear and extranuclear nitroquinoxalines... 

Gokalp, LG. Shepherd, and R.K. Cheng 1988, Spectral behavior of velocity fluctuations in premixed turbulent flames. Combust. Flame 71 (3) 313-323. 

Undoubtedly, the uniform structural and spectral behavior of the trigonal-planar jt-radicals (t-Bu2MeSi)E (E = Si, Ge, Sn) 43-45 both in the solid state and in solution should be ascribed to the immediate impact of the bulky electropositive silyl substituents. In contrast, it is well known that simple alkyl and aryl substituents cause a highly pronounced pyramidalization at the radical centers, where the unpaired electron typically occupies the orbital with a high s-contribution (o-radicals)7 ... 

The mass spectral behavior of several nuclear and extranuclear nitroquinoxalines has been investigated in some detail.290,763 The X-ray analysis of 5-nitro-2,3-bis(pyridin-2-yl)quinoxaline1115 and its bisperchlorate salt1113 have been reported. Reduction to quinoxalinamines is the main transformation of nitroquinoxalines, but they also undergo useful displacement reactions. 

The mass spectral behavior of tropane alkaloids is well documented (53,63,142,166-171), and only the most characteristic points will be noted here. The general fragmentation pattern of the 3-hydroxytropane esters can be described in terms of the following five routes (Routes A-E) (Scheme 29) (55). 

Quadrupole electron-impact (El) and chemical ionization (Cl) mass spectral behavior of some principal tropane alkaloids (e.g., 1,14,19,26,43,89, 96-98, and 124) has recently been reported (172). 

All these features were observed experimentally for solutions of 3-amino-/V-methylphthalimide, 4-amino-/V-methylphthalimide, and for nonsubstituted rhoda-mine. The results were observed for cooled, polar solutions of phthalimides, in which the orientational relaxation is delayed. Exactly the same spectral behavior was observed [50] by picosecond spectroscopy for low viscosity liquid solutions at room temperature, in which the orientational relaxation rate is much higher. All experimental data indicate that correlation functions of spectral shifts Av-l(t), which are used frequently for describing the Time Dependent Stokes Shift, are essentially the functions of excitation frequency. 

Pilla, P. Foglia Manzillo, P. Giordano, M. Korwin Pawlowski, M. L. Bock, W. J. Cusano, A., Spectral behavior of thin film coated cascaded tapered long period gratings in multiple configurations, Opt. Express 2008, 16, 9765 9780... 

These data, together with the molecular formula, indicated that the oxygen must be present as an ether bridge. If the doublet at 77.7 ppm is due to an aminomethine, the second carbon of the ether bridge should give rise to the singlet at 80.1 ppm. The only biosynthetically reasonable structures that could explain this spectral behavior are 2,14-oxidopseudoaspidospermidine (306) (without stereochemistry) or the new structure 173. Structure 306 was easily... 

It is remarkable that the n scale has been established from the averaged spectral behavior of numerous solutes. It offers the distinct advantage of taking into account both non-specific and specific interactions. 

In our discussion, solute refers to the substance whose resonances are being discussed (which may be racemic, enantiomerically enriched, or even a single enantiomer), and CSA to the substance whose chirality influences solute spectral behavior. Occasionally, for a given pair of compounds, these roles may be interchangeable. 

This interpretation was also supported by the spectra of the corresponding N-methyl-leucine derivative in which the H-donor of the selectand was substituted by a methyl group and therefore not available for hydrogen bonding. Both complexes showed a similar spectral behavior as the weak 5-complex of DNB-Leu The C=0 stretch was always shifted from 1725 (uncomplexed autoassociated selector) to 1739 cm (indicative for disrupted H-bonds) in the 5-complex and R-complex as well. These FT-IR data may be regarded as an unequivocal proof for the existence of a stereoselective H-bond between the NH of DNB-Leu and the selector s carbonyl group (Figures 1.10 and 1.11). 

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