Chiral centre, definition

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). 

Chiral centres encountered in anaesthetics usually have carbon or quaternary nitrogen as the chiral centre. Any compound which contains more than one chiral centre is termed a diastereoisomer by definition. 

The user specifies a desired upper limit on the number of steps in an acceptable synthesis. The user also specifies his lower limit on the overall yield. In addition there must be some kind of definition of what is an acceptably simple molecule, i.e. one whose structure is so simple that it can be assumed to be readily available or cheaply prepared. This definition is conveyed by the user in the form of the minimum number of chiral centres, rings and functional groups that are acceptable in a readily available material. In addition the structure of a preferred starting material can be input. Finally the structure of the goal molecule is provided by the user. Structures of molecules are communicated to the program in the form of... 

When the difference between substituents is in configuration, then in general Z> E and R> S. However, the formal definition is that an olefinic ligand in which the substituent of higher sequence priority is on the same side of the alkene double bond as the chiral centre takes priority. This definition does not correspond with either E,Z- or cis/trans- (change to the rules in 1982), The subscript n (for new ) is used in cases of doubt. 

A second area concerns the use of the word chiral. This has a specific definition and can only be properly applied to three-dimensional objects. Thus it is incorrect to refer to a chiral centre/axis or a chiral synthesis . The former can be a chirality centre/axis or a centre/axis of chirality although for most purposes we prefer to replace these terms by stereogenic centre/axis (which is, however, not equivalent). [51 As a collective term for enantio- and diastereoselective... 

Definition of the stereochemistry of heptoses, octoses and nonoses requires two prefixes, one defining the configuration at Oi—Cs as in a hexose, and the other, which appears first in the name, defining the configuration at the remaining chiral centre(s). The known aldoheptoses, aldooctoses, octuloses and nonuloses are tabulated in Reference [ 1 ], pp. 245-50. 

Chiral nematic liquid crystals, as the name suggests, are optically active variants of nematic liquid-crystalline compounds the incorporation of a chiral centre imparts properties which are unique to the chiral nematic phase and are responsible for their utilisation in a variety of differing display technologies and other related applications. The term cholesteric liquid crystal was originally used to describe this phase, and originates from the structural nature of the earliest chiral nematic liquid crystals which were derivatives of cholesterol [1,2], Nowadays, the term chiral nematic is used primarily because the materials are clearly derived from nematic type liquid crystals [3, 4], Despite these differences in definition, the terms cholesteric and chiral nematic phase are interchangeable and it is common to find references to either term in the literature. 

In the application of this general definition, it is possible to include an examination of the symmetry group to which a molecule belongs. Knowledge of its symmetry group allows us to say whether a molecule is chiral or not. The condition for a molecule to be chiral is that it has no element of inverse symmetry, that is it does not have a centre, a plane or an improper axis of symmetry (Figure 2.9). 

Little secure information exists on the detail of biosynthesis between cadaverine and the various alkaloids although the incorporation, in appropriate fashion, of three molecules of radioactive A -piperideine 6.18) into lupanine 6.54) has been recorded label from C-6 appeared at C-2, C-15, and, by inference, C-10, whereas C-2 label appeared at C-17, C-11, and, by inference, C-6 [38]. (Much less definitive results were obtained for matrine [36].) This was taken, together with a careful consideration of the chirality at the asymmetric centres of all the quinolizidine alkaloids, as evidence for rearrangement within the A -piperideine trimer 6.59) [38], formed from 6.18), leading to the quinolizidine alkaloids [38]. 

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