Chirality definitions

Chiral, definition of, 260 Chiral axis. See Stereogenic axis Chiral center. See Stereogenic center Chiral drugs, 273 Chiral molecules, 259—263, 290 absolute configuration, 267, 292 Fischer projection formulas, 271-272, 278, 280, 292-293... 

Clearly, the next step is the handling of a molecule as a real object with a spatial extension in 3D space. Quite often this is also a mandatory step, because in most cases the 3D structure of a molecule is closely related to a large variety of physical, chemical, and biological properties. In addition, the fundamental importance of an unambiguous definition of stereochemistry becomes obvious, if the 3D structure of a molecule needs to be derived from its chemical graph. The moleofles of stereoisomeric compounds differ in their spatial features and often exhibit quite different properties. Therefore, stereochemical information should always be taken into ac-count if chiral atom centers are present in a chemical structure. 

Analogous definitions and designations apply to molecules containing a chiral centre and a prochiral tetrahedral or trigonal centre. The plane containing the chiral and prochiral centres is called a diastereo-zeroplane (Y. Izumi, 1977). 

The same kind of spontaneous racemization oc curs for any as 1 2 disubstituted cyclohexane in which both substituents are the same Because such compounds are chiral it is incorrect to speak of them as meso compounds which are achiral by definition Rapid chair-chair interconversion however converts them to a 1 1 mixture of enantiomers and this mix ture IS optically inactive... 

Achiral (Section 7 1) Opposite of chiral An achiral object is supenmposable on its mirror image Acid According to the Arrhenius definition (Section 1 12) a substance that ionizes in water to produce protons Accord mg to the Br0nsted-Lowry definition (Section 1 13) a sub stance that donates a proton to some other substance According to the Lewis definition (Section 1 17) an electron pair acceptor... 

In the early days following the discovery of chirality it was thought that only molecules of the type CWXYZ, multiply substituted methanes, were important in this respect and it was said that a molecule with an asymmetric carbon atom forms enantiomers. Nowadays, this definition is totally inadequate, for two reasons. The first is that the existence of enantiomers is not confined to molecules with a central carbon atom (it is not even confined to organic molecules), and the second is that, knowing what we do about the various possible elements of symmetry, the phrase asymmetric carbon atom has no real meaning. 

Cone angle concepts, 2,1012-1028 chelate effects, 2,1012 definitions, 2,1015 models, 2,1015 phosphines chiral, 2,1014 polydentate, 2,1013 solubility effects, 2,1014 use, 2,1028... 

There are two possible structures for simple alkyl radicals. They might have sp bonding, in which case the structure would be planar, with the odd electron in ap orbital, or the bonding might be sp, which would make the structure pyramidal and place the odd electron in an sp orbital. The ESR spectra of CHs and other simple alkyl radicals as well as other evidence indicate that these radicals have planar structures.This is in accord with the known loss of optical activity when a free radical is generated at a chiral carbon. In addition, electronic spectra of the CH3 and CD3 radicals (generated by flash photolysis) in the gas phase have definitely established that under these conditions the radicals are planar or near planar. The IR spectra of CH3 trapped in solid argon led to a similar conclusion. " °... 

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