Organic chemistry structural isomerism

Partitioning of carbocations between addition of nucleophiles and deprotonation, 35, 67 Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutational isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudoration in permutational isomerization, 9, 25... 

An interesting, important, and common phenomenon in organic chemistry is that of structural isomerism. Consider a molecule having two carbon atoms, four hydrogen atoms, and two chlorine atoms (C2H4CI2). These atoms are capable of binding to each other in two different ways as shown. 

Optical isomerism is the result of a dissymmetry in molecular suhstitution. The basic aspects of optical isomerism are discussed in various textbooks of organic chemistry. Optical isomers (enantiomers) may have different physiological activities from each other provided that their interaction with a receptor or some other effector structure involves the asymmetric carbon atom of the enantiomeric molecule and that the three different substituents on this carbon atom interact with the receptor. The Easson-Stedman hypothesis assumes that a three-point interaction ensures stereospecificity, since only one of the enantiomers will fit the other one is capable of a two-point attachment only, as shown in figure 1.13 for the reaction with a hypothetical planar receptor. However, it is reasonable to assume that receptor stereospecificity can also undergo a change when the receptor conformation is altered by a receptor-drug interaction. 

Another important concept from organic chemistry that has an impact on polymer structure is that of isomerism. Recall that structural isomers are molecules that have the same chemical formula, but different molecular architectures. For example, there are two different types of propyl alcohols, both with the same formula, depending on where the —OH functional group is placed on the carbon backbone (see Figure 1.53). Another type of isomerism results in stereoisomers, in which the functional groups are... 

The methane molecule is a very important molecule in organic chemistry, the geometry around the tetravalent carbon atom being basic to the understanding of the structure, isomerism and optical activity of a very large number of compounds. It is a tetrahedral molecule belonging to the tetrahedral point group, Td. 

REARRANGEMENT (Organic Chemistry). These are reactions involving the transfer of an atom or group from one part of the molecule to another. Tautomcrism is a special case of rearrangements in which the two forms are in dynamic equilibrium. See Tautomerism in entry on Isomerism. When such reactions take place, the establishment of structural formulas becomes complex. Some of the better known rearrangements include ... 

Structural (or constitutional) isomers are compounds with the same molecular formulas but different structural formulas (that is, different arrangements of the atoms in the molecule). Isomerism is especially important in organic chemistry because of the capacity of carbon atoms to be arranged in so many different ways continuous chains, branched chains, and rings. Structural formulas can be written so that every bond is shown, or in various abbreviated forms. For example, the formula for n-pentane (n stands for normal) can be written as ... 

Nuclear Magnetic Resonance (NMR) spectroscopy is one of the most powerful analytical techniques in organic chemistry for elucidating the molecular structures of chemicals (1,2). Moreover, an NMR spectrum may be used like a fingerprint to identify a chemical by comparing it with its reference spectrum recorded from the authentic chemical under comparable conditions. The spectrum also reveals information on molecular conformation, isomerism, molecular dynamics, and diastereomers (3 6). 

Prismane is an example of another interesting strained compound. Because it contains three-membered rings fused with four-membered rings, it should be even more strained than cubane. Prismane was prepared in 1973. It is a liquid that is stable at room temperature but explosive under some conditions. In toluene at 90°C its half-life (the time it takes for one-half of the compound to decompose) is 11 h. Note that prismane is isomeric with benzene. In fact, it was one of the structures proposed for benzene in the early days of organic chemistry. 

A compound that has two or more alternate structures but the same molecular formula. Isomers differ in physical properties from each other. There are many different types of isomerism, e.g. structural, optical, functional group and geometrical isomerism. The term is most widely used in organic chemistry. 

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