Atoms stereogenic,

The great majority of known chiral compounds are naturally occurring organic substances, their molecules having one or more asymmetrically substituted carbon atoms (stereogenic atoms). Chirality is present when a tetrahedrally coordinated atom has... 

Polymerization of optically active isonitiiles, 72, also leads to the formation of helical polymers with a preferential screw sense (219-222). Various factors distinguish this system from the preceding ones In the isonitrile case no new stereogenic atoms are formed during polymerization the helices are rigid and there is no indication of conformational equilibrium in the system the formation of a preferential screw sense is very probably a kinetically controlled process. 

An intramolecular hetero-Diels-Alder reaction has been used to produce the cyclopentaquinoline core of a series of alkaloids <20030L2509>. They form in high diastereoselectivity, generating up to four contiguous stereogenic atoms (Equation 134). 

For an alkene to exhibit cis-trans isomerism, the two groups on one end of the double bond must be different and the two groups on the other end of the double bond must be different. That is, in terms of the following structure, A must be different from B, and D must be different from E. When this is the case, both of the carbons of the double bond are said to be stereocenters. A stereocenter or stereogenic atom is defined as an atom at which the interchange of two groups produces a stereoisomer. 

Stcreocenter or stereogenic atom (Section 6.1) An atom at which the interchange of two groups produces a stereoisomer. 

The term stereocenter (stereogenic atom) is not consistently defined. The original (Mislow) definition is given here. Some sources simply define it as a synonym for an asymmetric carbon (chiral carbon) or for a chirality center. 

The examples shown in Scheme 16, which are representative for all other sulfinates studied, demonstrate a high level of stereoselectivity (around 80-90% of the original enantiomeric excess is retained after switching the stereogenic atom from sulfur to carbon). Despite these encouraging results, the somewhat tedious and stereochemically unreliable preparation of the starting sulfinates [47] may be the reason for the reluctance of the chemical community to use this chemistry as an entry to enantiomerically pure 2-alkenyl sulfones. 

Compounds with Other Quadrivalent Stereogenic Atoms Any molecule containing an atom that has four bonds pointing to the comers of a tetrahedron will be optically active if the four groups are different. Among... 

Compounds with Tervalent Stereogenic Atoms. Atoms with pyramidal bond-ing might be expected to give rise to optical activity if the atom is connected to three different groups, since the unshared pair of electrons is analogous to a fourth group, necessarily different from the others. For example, a secondary or tertiary amine where X, Y, and Z are different would be expected to be chiral and thus resolvable. Many attempts have been made to resolve such compounds, but until 1968 aU of them failed because of pyramidal inversion, which is a rapid oscillation of the unshared pair from... 

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