Geometry and stability

General Properties oe Vinyl Cations A. Geometry and Stability 1. Theoretical Calculations 

Semi-empirical calculations for the simple vinyl cation C2H3+ have been reported by Hoffmann (1964) and by Yonezawa et ad., (1968). More rigorous calculations by Sustmann et ad. (1969) are based on a semi-empirical method based on the neglect of diatomic differential overlap (NDDO) calibrated to results of ab initio Hartree-Fock-Roothaan SCF calculations. Recent work by Hopkinson et al. (1971) is entirely based on a non-empirical LCAO-MO-SCF method. 

The calculations on the vinyl cation have been mainly concerned with the problem of linear (161) versus bridged structures (162). 

There is general agreement on the prediction that cation 161 is more stable than 162 and ab initio calculations indicate a difference of 18-5-25 kcal mol-1 which probably corresponds to the real difference in the gas phase (Sustmann et al., 1969). 

Dissection of charge distribution in a and v orbitals for the vinyl cation 161 indicates that the -n electrons are polarized toward the 

---

Surfactants provide several types of well-organized self-assembhes, which can be used to control the physical parameters of synthesized nanoparticles, such as size, geometry and stability within liquid media. Estabhshed surfactant assembles that are commonly employed for nanoparticie fabrication are aqueous micelles, reversed micelles, microemulsions, vesicles [15,16], polymerized vesicles, monolayers, deposited organized multilayers (Langmuir-Blodgett (LB) films) [17,18] and bilayer Upid membranes [19](Fig. 2). 

The integrals of the separated resonance absorptions provide a direct measure of the enantiomeric ratio from which the cc can be calculated. The chemical shift anisochrony of enantiomers (dR S<>) in the presence of a nonracemic chiral auxiliary compound is attributed to at least two contributions which are related to the geometry and stability of the resulting diastereomeric association complexes79 80 ... 

Kakiuchi, N., Marck, C., Rousseau, N., Leng, M., De Clerq, E. and Guschlbauer, W. (1982) Polynucleotide helix geometry and stability. Spectroscopic, antigenic and interferon-inducing properties of deoxyribose-, ribose-, or 2 -deoxy-2 -fluororibose-containing duplexes of poly(inosinic acid), poly(cytidylic acid). J. Biol. Chem., 257, 1924-1928. 

Apart from this, one could use the degree of pyramidalization at the central Si atom or geometrical distortions of solvent molecule(s) S or counterion(s) X interacting with R3Si+ in solution. However, direct determination of geometry and stability of an ion R3Si(S)+ in solution by experimental means is difficult. In... 

It is interesting to note that the geometry and stability of the model complex are more important than the particular identity of the donors in modeling the hydrolytic zinc enzymes. Ligands such as L2 (32) appear to be closer mimics of the active site donors than the amine macrocycles but the water molecule in [Zn(L2)(H20)] " has a p/C, of 8.3. 

Molecular Geometry and Stability Solid and Solution Phase Analysis of A/,AT-disalicylaldehyde-1,3-propanediimine nickel(ll)... 

The first row d8 transition metal ion, nickel(II) provides an excellent system in which to investigate how the nature of the metal ion and its ligands affect coordination number, geometry, and stability. Nickel(II) offers a plethora of stereochemistries with various ligands and, further, complexes of the same chemical constituency can adopt different geometries with a range of stabilities. This behavior of nickel(II) complexes was first noted in 1939 by coordination chemist Lifschitz and his co-workers. Lifschitz reported that several... 

MOLECULAR GEOMETRY AND STABILITY SOLID AND SOLUTION PHASE ANALYSIS... 

---