Double bonds chiral nomenclature

A useful atlas of chiral molecules has appeared the major monoterpenoids of known absolute configuration are illustrated, with a literature coverage to the end of 1971.3 The reader should beware of printing errors e.g. (+)-/ -irone lacks a methyl group at C-2, (—)-(R)-a-cyclogeraniol lacks a double bond between C-2 and C-3, and (+)-S-carotene has only 39 carbon atoms (p. 131) carvotanacetone is incorrectly indexed and the nomenclature and presentation of thujane monoterpenoids is different from that used in these Reports. 

Ethylene and propylene are molecules that possess different symmetry (Figure 12.3). Ethylene has two C2 rotation axes and a a mirror plane. Propylene, owing to the presence of the methyl group, possesses only a a mirror plane (the double bond plane). The first consequence of this difference is that propylene has two chiral faces with respect to the plane defined by the double bond. In this respect, each face should be regarded as an enantioface. In Figure 12.3, the enantiofaces are indicated using the si and re nomenclature. ... 

In this section we present the elements of chirality relevant to the stereospecific polymerization of propene with group 4 metallocenes. First of all, coordination of a prochiral olefin, such as propene, gives rise to nonsuperimposable coordinations. To distinguish between the two propene coordinations, we prefer the nomenclature re, si—defined for specifying heterotopic half-spaces— instead of the nomenclature R,. defined for double or triple bonds jr-bonded to a metal atom—in order to avoid confusion with the symbols R and S used for other chiralities at the same catalytic site, or the nomenclature Re, Si-defined for reflection—variant units—and used by Pino and co-workers in refs 83—86. The use of the si, re nomenclature can be confusing when different monomers are considered, because the name of a fixed enantioface of an 1-olefin depends on the bulkiness of the substituent in position 1. However, since propene is the only monomer considered in this review, this problem does not exist here. We only remark that the re and si coordinations sketched in Scheme 3 correspond to the R and S coordinations, respectively. 

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