Organic compounds molecular geometry

Hehre, W.J. Pople, J.A. Lathan, W.A. Radom, L. Wasserman, E. Wasserman, Z.R. Molecular orbital theory of the electronic structure of organic compounds 28. Geometries and energies of singlet and triplet states of the C3H2 hydrocarbons. J. Am. Chem. Soc. 1976, 98, 4378-4383. 

A somewhat dilferent way to define a molecule is as a simplified molecular input line entry specification (SMILES) structure. It is a way of writing a single text string that defines the atoms and connectivity. It does not define the exact bond lengths, and so forth. Valid SMILES structures for ethane are CC, C2, and H3C-CH3. SMILES is used because it is a very convenient way to describe molecular geometry when large databases of compounds must be maintained. There is also a very minimal version for organic molecules called SSMILES. 

Although reservations have been expressed concerning VSEPR as an explanation for molecular geometries it re mains a useful too/for pre dieting the shapes of organic compounds... 

So far we have emphasized structure in terms of electron bookkeeping. We now turn our attention to molecular geometry and will see how we can begin to connect the three-dimensional shape of a molecule to its Lewis formula. Table 1.6 lists some simple compounds illustrating the geometries that will be seen most often in our study of organic chemistry. 

Short intramolecular contacts between chalcogens and other chalcogens or other heteroatoms have been shown to influence molecular geometry, particularly planarity, in many structures of electroactive materials. Hence the position of the chalcogen atom in the material can profoundly affect its properties. For example Crouch et al 2 report the X-ray crystal structure of compound 24 (Figure 10), a candidate for an organic field-effect transistor, showing the effect of intramolecular S- F close contacts (in tandem with H F contacts) on the planarity of the molecule in the solid state. Note also the... 

Fig. 5 A proposed mechanism for enhanced emission (or AIEE) in solid-state organic dye nanoparticles. The dye considered here is trans-biphenylethylene (CN-MBE) compound. The geometry is optimized by the density functional theory (DFT) calculation at the B3LYP/6-31G level. Molecular distortion such as twisting and/or subsequent planarization causes prevention of radiationless processes along with specific aggregation such as the /-aggregate in the nanoparticles...

An excited state has a finite lifetime and so it has static properties, such as molecular shape (median bond lengths and angles) and dipole moment, like those of a ground-state molecule, that can in principle be determined experimentally. However, the lifetime of an excited state is short, often very short, and this restricts the range of techniques that can be employed to study such properties. Most of the available information comes from high-resolution absorption 01 emission spectra, particularly of small or symmetrical model compounds. The geometry of most other excited organic molecules has to be inferred from such results. 

It is clear from the preceding section that the field of tethered arene-metal complexes is dominated by ruthenium and by arene-phosphines as ligands. In part, this situation has arisen because of the current surge of interest in the catalytic properties of ruthenium complexes in organic synthesis.85,86 Moreover, the tethered arene complexes are usually air-stable, crystalline solids with a well-defined, half-sandwich molecular geometry that, in principle, can lock the configuration at the metal centre. These compounds should, therefore, be ideal both for the study of the stereospecificity of reactions at the metal centre and for stereospecific catalysis. 

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