Theoretical and Structural Studies

MINDO calculations of the molecular geometries of diazaheterocyclic 1,2-dienes indicated that diazocine 183 has more allenic character than the seven- and six-membered ring homologues (although all three have largely allenic structures) (82JCR(S)80). 

Urbanski and co-workers prepared a number of 1,5-diazocines (see Section II,C,1) and investigated their conformations. In one study, molecular refractions were determined for compounds 101 (cis and trans, R = Me, Et, n- Pr R1 = H). Infrared spectra of these compounds showed both bonded NH2 and NOz groups the compounds formed only monohydrochlorides and mononitroso derivatives. These facts suggested intramolecular hydrogen bonding between the two ring nitrogen atoms. The experimental dipole moment of trans-101 (R = Et, R1 = H) was consistent with that calculated for a crown conformation (184), with the two 

The naphthodiazocine monocation 185 was found to undergo 100% equilibrium N-protonation. This was in contrast to the 9- and 10-memb-ered ring homologues, which underwent 100% C-protonation on the naphthalene nucleus to give an sp2-hybridized imminium ion C=N +. This phenomenon is believed to be favored in medium rings. However, models of C-protonated 185 did seem strained (82JCS(P2)477). 

In a study of Troger s base derivatives 68 [R = H, Me RR = (CH2)3] in acid media (see Section II,B,3), Greenberg et al. found the dication of the dimethyl derivative (186, R = Me) to have nonidentical benzylic methylene groups and nonequivalent methyl NMR resonances. These results are consistent with the open iminium ion structure 69 (R = Me), and contrast with the results with Troger s base itself (68, R = H) and its spiro (cyclobutyl) derivatives 68 [RR = (CH2)3], in which the protonated closed structure 186 [RR = (CH2)3M] is favored (84JOC1127). 

Reaction of diazocine 190 (see Section II,A,3) with phosgene afforded the oxadiazolone derivative 191 (79CPB2608). As mentioned earlier (see Section II,B,1), annelated diazocine 51 accompanied 50 (R = R1 = H) as a product of the Schmidt reaction of 1,3-cyclohexanedione. It was postulated, on the basis of ring-opened hydrolysis products (see Section IV,D), that 51 arose from annelation of 50 (R = R1 = H). [A 1,4-diazo-cinedione and its annelation product were also obtained (89AHC185), but it was determined that in this case annelation occurred at the intermediate seven-membered p-ketolactam stage, not on the diazocine that followed.] 

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Theoretical and structural studies have been briefly reviewed as late as 1979 (79AHC(25)147) (discussed were the aromaticity, basicity, thermodynamic properties, molecular dimensions and tautomeric properties ) and also in the early 1960s (63ahC(2)365, 62hC(17)1, p. 117). Significant new data have not been added but refinements in the data have been recorded. Tables on electron density, density, refractive indexes, molar refractivity, surface data and dissociation constants of isoxazole and its derivatives have been compiled (62HC(17)l,p. 177). Short reviews on all aspects of the physical properties as applied to isoxazoles have appeared in the series Physical Methods in Heterocyclic Chemistry (1963-1976, vols. 1-6). 

The aromaticity of isoxazole has been reviewed in terms of theoretical and structural studies,138 139 and the conclusion is that it is slightly less aromatic than oxazole and furan. 

Research in the reviewed period 1995-2005 has covered more the chemistry of 1,3,2-dithiazoles and less the chemistry of 1,3,2-dioxazoles. 1,3,2-Oxathiazoles and their derivatives were not investigated in this period. Much attention has been paid to the neutral 1,3,2-dithiazolyl radicals including their synthesis, theoretical and structural study, and application. Special attention was given to their magnetic properties and conductivity. 1,3,2-Benzodithiazole. Y-oxidcs were of interest as enantiomeric compounds and intermediates for the preparation of enantiopure amines and alcohols. 

There has been a considerable expansion in the use of C NMR in theoretical and structural studies since the publication of CHEC-I in 1985, but in many instances C NMR data is recorded for the purposes of characterization without detailed assignment of the chemical shifts. Selected assigned data from the review period for pyridazines and pyridazinones is shown in Table 1. Compared with these aromatic systems, dihydropyridazinones show normal C shifts as shown by the methylene 25.9 and 23.8) and carbonyl 5 166.6) carbons of 6-benzyl-4,5-dihydro-3(2//)-pyridazinone in DMSO <89JHC1787>. Care should be taken in making comparisons involving potentially tautomeric systems like the pyridazinones note, for instance, the equivalence of 3,6- and... 

The combined use of theoretical and structural studies allows one to establish the existence of the mutual influence of different structural parameters, usually referred to as structural correlations. Such correlations are useful for predicting or explaining the structural data for new compounds. In particular, they should ultimately allow one to make predictions on compounds with extreme bonding situations, i.e., very weak or very strong bonds. 

We ve included several papers in the References section which perform theoretical and experimental studies of the IR and Raman spectra for these compounds. These compounds were among the earliest ab initio frequency studies of such systems. In addition, in the case of propellane, theoretical predictions of its energy and structure preceded its synthesis. 

Numerous theoretical and experimental studies have dealt with the properties of rutile (see 3 and references therein), while the other polymorphs have attracted less attention. This is due to the fact that rutile is easier to grow and characterize, and has a simpler structure that can be readily investigated using a variety of theoretical techniques. The fact that the experimentally reported bulk modulus of anatase is in the range from 59 GPa to 360 GPa illustrates the need for further studies of titanium dioxide polymorphs. 

Two-phase flows in micro-channels with an evaporating meniscus, which separates the liquid and vapor regions, have been considered by Khrustalev and Faghri (1996) and Peles et al. (1998, 2000). In the latter a quasi-one-dimensional model was used to analyze the thermohydrodynamic characteristics of the flow in a heated capillary, with a distinct interface. This model takes into account the multi-stage character of the process, as well as the effect of capillary, friction and gravity forces on the flow development. The theoretical and experimental studies of the steady forced flow in a micro-channel with evaporating meniscus were carried out by Peles et al. (2001). These studies revealed the effect of a number of dimensionless parameters such as the Peclet and Jacob numbers, dimensionless heat transfer flux, etc., on the velocity, temperature and pressure distributions in the liquid and vapor regions. The structure of flow in heated micro-channels is determined by a number of factors the physical properties of fluid, its velocity, heat flux on... 

It is well known that the energy profiles of Compton scattered X-rays in solids provide a lot of important information about the electronic structures [1], The application of the Compton scattering method to high pressure has attracted a lot of attention since the extremely intense X-rays was obtained from a synchrotron radiation (SR) source. Lithium with three electrons per atom (one conduction electron and two core electrons) is the most elementary metal available for both theoretical and experimental studies. Until now there have been a lot of works not only at ambient pressure but also at high pressure because its electronic state is approximated by free electron model (FEM) [2, 3]. In the present work we report the result of the measurement of the Compton profile of Li at high pressure and pressure dependence of the Fermi momentum by using SR. 

Finally, the chemical properties of the new structures available from disilene addition reactions have hardly been touched. In future developments, theoretical and experimental studies are likely to proceed together and complement one another, as they have from the beginning days of this research. 

Hydroxyl radical (OH) is a key reactive intermediate in combustion and atmospheric chemistry, and it also serves as a prototypic open-shell diatomic system for investigating photodissociation involving multiple potential energy curves and nonadiabatic interactions. Previous theoretical and experimental studies have focused on electronic structures and spectroscopy of OH, especially the A2T,+-X2n band system and the predissociation of rovibrational levels of the M2S+ state,84-93 while there was no experimental work on the photodissociation dynamics to characterize the atomic products. The M2S+ state [asymptotically correlating with the excited-state products 0(1 D) + H(2S)] crosses with three repulsive states [4>J, 2E-, and 4n, correlating with the ground-state fragments 0(3Pj) + H(2S)[ in... 

An experimental study of barbituric acid found one new polymorph where molecules in the asymmetric unit adopted two different conformations [10]. The conformational aspect was investigated through the use of ab initio calculations, which permitted the deduction that the new form found would have a lower lattice energy than would the known form. It was also found that many hypothetical structures characterized by a variety of hydrogen-bonding structures were possible, and so the combined theoretical and experimental studies indicated that a search for additional polymorphs might yield new crystal structures. 

This chapter is concerned with the application of liquid state methods to the behavior of polymers at surfaces. The focus is on computer simulation and liquid state theories for the structure of continuous-space or off-lattice models of polymers near surfaces. The first computer simulations of off-lattice models of polymers at surfaces appeared in the late 1980s, and the first theory was reported in 1991. Since then there have been many theoretical and simulation studies on a number of polymer models using a variety of techniques. This chapter does not address or discuss the considerable body of literature on the adsorption of a single chain to a surface, the scaling behavior of polymers confined to narrow spaces, or self-consistent field theories and simulations of lattice models of polymers. The interested reader is instead guided to review articles [9-11] and books [12-15] that cover these topics. 

In addition to pure water, we extended our investigation on solvated Li+ to NH3 (90), NH3-H20 mixtures (91), dimethylsulf-oxide (DMSO) (92), DMS0-H20 mixtures (92), HCN and CH3CN, and their mixtures with water (93). For NH3 as a water-like solvent, all published X-ray structures are tetrahedrally coordinated, [Li(NH3)4] + (94-97). Therefore, we expect to have [Li(NH3)4]+ in solution. The validity of this assumption is also supported by the exchange mechanism. In the case of DMSO, a variety of theoretical and experimental studies on liquid DMSO (98-104), DMSO-water mixtures (105-110), DMSO-non-aqueous... 

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