Molecular structure stereoisomer

A theoretical analysis is presented for the binding of the four dia-stereoisomers of benzo[a]pyrene diol epoxides (BPDEs) to N2(g), N6(a), 06(G) and NU(c). Molecular models for binding and stereoselectivity involving intercalation, intercalative covalently and externally bound forms are presented. Molecular mechanics calculations provide the energetics which suggest possible structures for the formation of each of the principal DNA-BPDE complexes. Stereographic projections are used to illustrate the molecular structures and steric fits. The results of previous calculations on intercalation and adduct formation of BPDE l(+) in kinked DNA (37) are summarized and extended to include the four diastereoisomers l( ) and II( ). The theoretical model is consistent with the observed experimental data. 

Stereochemical aspects in mass spectrometry have aroused more and more interest. El mass spectra of stereoisomers are practically indistinguishable. However, the use of soft ionization methods (chemical ionization, field ionization, etc.) accompanied by tandem mass spectrometry allows important and reliable conclusions on the molecular structures to be drawn. 

The term oxime dates to the 19th century, a combination of the words oxygen and imide. Oximes exist as two stereoisomers syn (Z) and anti (E). Aldoximes, except for aromatic aldoximes, exist for the most part as the syn isomer, while ketoximes are obtained as both syn and anti isomers, which can be separated almost completely. Recently, Kolandaivel and Senthilkumar have studied the molecular structure and conformational stability of anti and syn conformers of some aliphatic aldoximes by employing the ab initio and density funetional theory (DFT) methods. 

Figure 5 Molecular structures of the (+)-/rans-a/i/i-[BP]-,/V2-dG and (-)-cis-anti-[BPJ-A dG adducts formed from the metabolically activated form of the widespread environmental polutant benzo[a]pyrene (BP) and dG. These two adducts have the same S-configuration about the a/i/HBPJ-ClO-A -dG linkage but different arrangements of the OH groups at the 7, 8, and 9 positions of the a/i//-[BP] residue. Each of these two diastereoisomers also has a corresponding stereoisomer with a 10R configuration at CIO (not shown).

Enantiomers Stereoisomers whose molecular structures are related as an object to its mirror image but that can t be superimposed. 

The molecules of MSG can exist in two different forms known as isomers. These isomers are chemically identical, but physically different because their molecular structures are dissimilar. In fact, the elements on the two MSG isomers, known as stereoisomers, are arranged in such a way that if they were placed next to each other, they would appear as mirror images. The isomers of MSG have different physiological effects, and only one of them, known as the L form, has flavor enhancing properties. 

In Chap. 4, we learned that stereoisomers exist of the kind called enantiomers (mirror-image isomers), that they can be optically active, and that both their existence and their optical activity are the result of the chirality of certain molecules, that is, of the non supe iinposability of such molecules on their mirror images. We learned how to predict, from a simple examination of molecular structure, whether or not a particular compound can display this kind of isomerism. We learned how to specify the configuration of a particular enantiomer by use of the letters R and S. 

The relationship between the molecular structure of a chemical compound and its odor has been the subject of much research and conjecture. It is still not possible to predict the aromatic profile from the structure of a given chemical, and it is not possible to assume changes in flavor profile based on molecular structure modification. Even stereoisomers may differ in odor both qualitatively and quantitatively. Nevertheless, the relationship between structure and odor can be summarized as follows. 

When we examine the molecular structures and functional groups of known pheromones, we find that they have little in common. Some pheromones contain stereoisomers, and some insects can distinguish between the stereoisomers. The strucmres of pheromones play vital roles in their activity. Part of the structure is an upper limit of about 20 carbon atoms, a limit probably imposed by Graham s Law. Most pheromones must travel through the air those with low molecular weights are often more volatile. Scientists suspect that the physical motions of pheromone molecules, which are also a function of molecular strucmre, play an important role in the communication mechanism. 

Enantiomer Stereoisomers whose molecular structures are non-superimposable mirror images. 

MOLGEN+, a generator of connectivity isomers and stereoisomers for molecular structure eludication. Anal. Chim. Acta 314,141-147. 

Stereoisomers Rotation of Plane-Polarized Light The Relationship between Molecular Structure and Optical Activity Fischer Projection Formulas... 

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