Chiral flags

The first line of the connection table, called the counts line (see Figure 2-21), specifies how many atoms constitute the molecule represented by this file, how many bonds arc within the molecule, whether this molecule is chiral (1 in the chiral flag entry) or not, etc. The last-but-onc entry (number of additional properties) is no longer supported and is always set to 999. The last entry specifics the version of the Ctab format used in the current file. In the ease analyzed it is V2000". There is also a newer V3000 format, called the Extended Connection Table, which uses a different syntax for describing atoms and bonds [50. Because it is still not widely used, it is not covered here. 

Figure 5-28. Reaction query for Example 2 "R indicates that the bond must be part of a ring system, and "53 represents an atom with three non-hydrogen attachments. The Chiral" flag is necessary to retrieve only molecules with the identical absolute stereoconfiguration.

Add chiral flag If the compound has a single stereo center, a chiral flag should be present ... 

Remove chiral flag If a structure does not have a stereo center, the chiral flag should not be present ... 

Figure 9.5. Defining absolute, relative collection, and relative single configuration stereochemistry. The older convention depends on a "chiral" flag on the molecule to specify whether a given structure represents one or several stereoisomers. In the newer convention, collections of stereo centers can be defined, and they can be designated absolute, relative-part-of-a-mixture, or relative-single-configuration.

Mean E E-l = 0.510 [expected. 968 centrosym and. 736 non-centrosym] Chiral flag NOT set Systematic absence exceptions ... 

When racemic 2-ethylpiperidine was reacted with the provisional chiral conformation of 3a, similar results were obtained as the reaction with 2-methylpiperidine. However, when racemic 3-methylpiperidine was used as a nucleophile, the substitution reaction occurred quantitatively however, the ee value resulted in 17%. The methyl group at the 3-position of the paperidine ring was insufficient to control the stereoselectivity because of the distance between the reacting nitrogen atom and the substituent. On the contrary, the substituent at the 2-positions worked sufficiently as strong chiral flags to control the stereoselectivity. 

SCHEME 1. Access to optically active compounds Structure relationship between the chiral source and chiral products (flags refer to right- or left-handed molecules). 

Giancarlo, L.C. and Flynn, G.W., Raising flags Applications of chemical marker groups to study self-assembly, chirality, and orientation of interfacial films by scanning tunneling microscopy, Acc. Chem. Res. 33, 491-501, 2000. 

Ciancarlo. L. Flynn, C.W. Raising flags Application of chemical marker groups to study self-assembly, chirality. 

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