Different spectra: structural data

Note added in proof. Kamb, Hamilton, LaPloca and Prakash [J. Chem. Phys. 55, 1934 (1971)] have argued, from the comparison of the infrared absorption spectrum of HDO/H2O ice II and crystal structure data, that there is no correlation between vod and hydrogen bond donor angle. Instead, for this case they establish a correspondence between j>od and 00 separation. This interpretation differs from that offered by VRB for high density HaO(as). 

With this in mind, the coordination chemistry of 52 with different diazine structural isomers was investigated. There were no detectable changes in the H NMR spectrum of 52 in a THF-Jg solution when either pyrazine or pyrimidine were added in 1 1 or 1 2 molar ratios, which suggested that only weak interactions might occur between 52 and these bases. In contrast, incremental addition of pyridazine or phthalazine to a THF-Jg solution of 52 at 25 °C resulted in an upheld shift of the aromatic NMR resonances of the diindacycle 52 thus reflecting the formation of complexes between 52 and the 1,2-diazines. Analysis of the tritration data clearly indicated the formation of 1 1 Lewis acid-diazine complexes 52-pyridazine-(THF)2 and 52-phthalazine-(THF)2 whose stability constants are equal to 80 ( 10) and 1000 ( 150) M respectively (Scheme 29). These data, as a whole, indicate that 52 is a selective receptor for 1,2-diazines. 

The structural data from which the structure of vinoxine (89) was deduced have been described in greater detail.65 The configuration at C-16 is based on the closer resemblance of the XH n.m.r. spectrum of vinoxine to that of 16-epipleiocarpamine rather than that of pleiocarpamine. In reference 65, for some unspecified reason, the configuration given for the double bond is different from that illustrated in (89) and postulated in the earlier communication 334 however, the similarity of the chemical shifts of the protons of the ethylidene group with the corresponding ones in the pleiocarpamine series makes it extremely probable that the configuration about the double bond [i.e. (Ij)] is the same in all these alkaloids. 

Souz et al. synthesized and structurally characterized a tetramer complex [Eu4(ETA)9(OH)3 (H20)3l (see Figure 2.42 [76], where ETA = ethyl 4,4,4-trifluoroacetoacetate. From these structural data, they calculated the ground-state geometry of the tetramer by using the Sparkle/AMl model. The emission spectrum shows that the Dq Fq transitions in the emission spectrum are consistent with the Eu + ion occupying four different sites in chemical environments of low symmetries. 

If the difference in atomic number between the absorber element and the backscattering element is >10 and if only one kind of element backscatters, EXAFS spectra can be analyzed readily to provide local structural data on adsorbed species. However, because the electron mean free path, thermal and static disorder parameters (Debye-Waller factors), and coordination number for an absorber environment cannot be determined a priori with sufficient accuracy, EXAFS data for suitable reference compounds of known molecular structure must be used to help interpret the EXAFS spectrum for an interfaeial region. 

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