Organic molecules, shapes

Alkenes are hydrocarbons that contain a carbon-carbon double bond A carbon-carbon double bond is both an important structural unit and an important func tional group m organic chemistry The shape of an organic molecule is influenced by the presence of this bond and the double bond is the site of most of the chemical reactions that alkenes undergo Some representative alkenes include isobutylene (an industrial chemical) a pmene (a fragrant liquid obtained from pine trees) md fame sene (a naturally occurring alkene with three double bonds)... 

Of the various geometric parameters associated with molecular shape, the one most nearly constant from molecule to molecule and most nearly independent of substituent effects is bond length. Bond lengths to carbon depend strongly on the hybridization of the carbon involved but are little influenced by other factors. Table 1.2 lists the interatomic distances for some of the most common bonds in organic molecules. The near constancy of bond lengths from molecule to molecule reflects the fact that the properties of individual bonds are, to a good approximation, independent of the remainder of the molecule. 

We saw in the last chapter how covalent bonds between atoms are described, and we looked at the valence bond model, which uses hybrid orbitals to account for the observed shapes of organic molecules. Before going on to a systematic study of organic chemistry, however, we still need to review a few fundamental topics. In particular, we need to look more closely at how electrons are distributed in covalent bonds and at some of the consequences that arise when the electrons in a bond are not shared equally between atoms. 

For some compounds, it is especially useful to know the shape of the molecule. While this is critically important in large molecules made with a backbone of carbon, called organic molecules, it is often interesting in simpler molecules as well. The formula for water might cause you to think that a hydrogen atom was attached to another hydrogen atom, and then an oxygen atom was attached to them ... 

Recently, a symmetry rule for predicting stable molecular shapes has been developed by Pearson Salem and Bartell" . This rule is based on the second-order, or pseudo, Jahn-Teller effect and follows from the earlier work by Bader . According to the symmetry rule, the symmetries of the ground state and the lowest excited state determine which kind of nuclear motion occurs most easily in the ground state of a molecule. Pearson has shown that this approximation is justified in a large variety of inorganic and small organic molecules. 

Figure 3. Several strategies on controlling the shape of nanoparticles (a) organic molecules or polymers as capping agents, (b) inorganic molecules as face-selective catalysts, and (c) inorganic molecules as face-selective etchants.

What are the shapes of some organic molecules Can the same number of atoms be arranged differently ... 

The present volume gives a general and at the same time rather detailed review on main research developments in the field of dendrimers (oligomer and polymer) during the past several years, but also offers views and visions of the future - of what could soon be achieved in this area at the interface between small organic molecules and macromolecules (polymers). We are sure that the rapid development of fractal-shaped molecules will continue in academic institutes as well as in industry - there is still more to come. 

The great importance of minerals in prebiotic chemical reactions is undisputed. Interactions between mineral surfaces and organic molecules, and their influence on self-organisation processes, have been the subject of much study. New results from Szostak and co-workers show that the formation of vesicles is not limited to one type of mineral, but can involve various types of surfaces. Different minerals were studied in order to find out how particle size, particle shape, composition and charge can influence vesicle formation. Thus, for example, montmorillonite (Na and K10), kaolinite, talc, aluminium silicates, quartz, perlite, pyrite, hydrotalcite and Teflon particles were studied. Vesicle formation was catalysed best by aluminium solicate, followed by hydrotalcite, kaolinite and talcum (Hanczyc et al., 2007). 

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