Structure and spectroscopic properties

The infrared spectrum of di-0-trityl-3 -ketouridine 2, in comparison with that2 of the parent 1, exhibited an additional carbonyl band at 1775 cm-1. 

The presence of a 3 -keto function in 18a was confirmed by a carbonyl band at 1780 cm-1, in addition to those present at 1720 and 1675 cm-1 in the i.r. spectrum of the parent nucleoside 17a. Similarly, a new carbonyl band appeared at 1780 cm-1 in the spectrum25 of the 2 -keto-cytidine derivative 20a. 

The 5 -0-trityl 3 -ketothymidine 33b exhibited an i.r. absorption at 1778 cm-1, attributed to the keto group introduced.44 Also, theophylline 4 -ketonucleoside derivative 41a had26,27 an i.r. spectrum similar to that of the parent 40a, except for a carbonyl band at 1755 cm-1. Thymine 4 -ketonucleoside derivative 45 exhibited a carbonyl band at 1725 cm-1, assigned to the C=0 and -C(=0)-C=C- groups of the base.30 The 

In the case of 2 -ketonucleosides, this shifting of the H-l resonance is further enhanced by the purine or pyrimidine ring. 

Some characteristic results are as follows. The n.m.r. spectra2 of 2 -ke-touridines 2 and 3 showed the H-l signal as sharp singlets at 8 5.79 and 5.42, respectively, and J3.4. as a doublet in both cases, confirming the absence of a proton at C-2.  

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Inadequate availability of experimental data can considerably inhibit the development of improved energy functions for more accurate simulations of energetic, structural, and spectroscopic properties. This has led to the development of class II force fields such as CFF and the Merck Molecular Force Field (MMFF), which are both based primarily on quantum mechanical calculations of the energy surface. The purpose of MMFF, which has been developed by Thomas Halgren at Merck and Co., is to be able to handle all functional groups of interest in pharmaceutical design. 

Extensive quantum chemical calculations have been reported for sulfur-rich compounds in the past two decades. These calculations were used to investigate molecular structures and spectroscopic properties, as well as to understand the nature chemical bonding and reaction mechanism. Many high-level ab initio calculations were used for interpretation of experimental data and for providing accurate predictions of molecular structures and thermochemical data where no reliable experimental values are available. In recent years, density functional calculations have been extensively tested and used on many first- and second-row compounds. These proven DFT methods look promising for larger systems because for their computational efficiency. 

Chan, M.C.-W. and Che, C.-M. (1998) Application of 2,6-diphenylpyridine as a tridentate [C N C] dianionic ligand in organogold(III) chemistry. Structural and spectroscopic properties of mono- and binuclear transmetalated gold(III) complexes. Organometallics, 17, 3505-3511. 

B. Hydroxide Derivatives of Zinc and Cadmium 1. Syntheses, Structures, and Spectroscopic Properties... 

Biomimetic chemistry of nickel was extensively reviewed.1847,1848 Elaborate complexes have been developed in order to model structural and spectroscopic properties as well as the catalytic function of the biological sites. Biomimetic systems for urease are described in Section 6.3.4.12.7, and model systems for [Ni,Fe]-hydrogenases are collected in Section 6.3.4.12.5. 

From the standpoint of modeling Type I copper proteins,4,5,59,60 a variety of imidazole-based ligands containing thioether sulfurs and imidazole groups have been synthesized.61,62 The structures and spectroscopic properties of their copper(II) complexes (51)-(53) and (55)-(60) were investigated.65,79-82 To characterize apical copper(II)-thioether bonding, the complex (51) was... 

Although continuum solvation models do appear to reproduce the structural and spectroscopic properties of many molecules in solution, parameterization remains an issue in studies involving solvents other than water. In addition, the extension of these approaches to study proteins embedded in anisotropic environments, such as cell membranes, is clearly a difficult undertaking96. As a result, several theoretical studies have been undertaken to develop semi-empirical methods that can calculate the electronic properties of very large systems, such as proteins28,97 98. The principal problem in describing systems comprised of many basis functions is the method for solving the semi-empirical SCF equations ... 

During the last few years, both neutral and cationic 1,3,2-diazaphospholes and NHP have been studied extensively by computational methods. The best part of these studies focused on a discussion of n-electron delocalization and their implication on chemical reactivities and stabilities, the explanation of the unique ionic polarization of exocyclic P-X bonds noted for some species, and the evaluation of structural and spectroscopic properties with the aim of helping in the interpretation of experimental data. 

Electronic Structure and Spectroscopic Properties of Molybdenum and Tungsten N2, NNH, NNH2, and NNH3 Complexes with Diphosphine Co-Ligands Insights into the End-on Terminal Reduction Pathway of Di nitrogen Felix Tuczek... 

We have already pointed out in the Introduction (see above) that the first review article on radialenes is only a few years old1. In this first summary we have enclosed a comprehensive survey and discussion of the structural and spectroscopic properties of the radialenes. Since progress in this latter area has not been very rapid in the last few years, we do not address here again these aspects of the radialenes. Furthermore, nothing new can be added to the statement that all radialenes are nonaromatic and that they have localized endocyclic single bonds and exocyclic double bonds1 (for recent discussions of ji-ji interaction in [5]- and [3]radialene, see elsewhere903 109). 

In summary, we can say that, because of the unique absence of angular and radial nodes in the H-atom valence shell, the hydride oah orbital is uniquely suited to strong n-a donor-acceptor interactions with Lewis bases. In turn, the unique energetic and angular features of nB-aAH interactions (or equivalently, of B H—A <—> B—H+ A covalent-ionic resonance) can be directly associated with the distinctive structural and spectroscopic properties of B - H—A hydrogen bonding. 

Table 1 Selected structural and spectroscopic properties of /V-acyloxy-iV-alkox yam ides 31b and 31f, -urea 38i, -carbamate 39g, theoretical models 40 and 41 and 1-aza-2-adamantanone 1...

Proton and 13C NMR spectral data of 33 derivatives of 64 have been tabulated and assigned <1996MRC409>. Several 3-oxo derivatives of 64 have been studied by proton and 13C NMR spectroscopy as part of a comprehensive investigation of their structural and spectroscopic properties <2003BCJ2361>. The regioselectivity of the formation of the six-membered ring in derivatives of 67 from 1,3-diketones has been established by proton NMR spectroscopy and nuclear Overhauser effects <1997CHE535>. 

III. Crystal and Solution Structure, and Spectroscopic Properties of the Gulono-1,4-lactones and Derivatives... 

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