StereoisomerismIn stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the same molecular formula, but the bond connections or their order differs. By definition, molecules that are stereoisomers of each other represent the same structural isomer.
Cis–trans isomerismCis–trans isomerism, also known as geometric isomerism or configurational isomerism, is a term used in chemistry that concerns the spatial arrangement of atoms within molecules. The prefixes "cis" and "trans" are from Latin: "this side of" and "the other side of", respectively. In the context of chemistry, cis indicates that the functional groups (substituents) are on the same side of some plane, while trans conveys that they are on opposing (transverse) sides.
IsomerIn chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ.
Enantiomeric excessIn stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%. A sample with 70% of one enantiomer and 30% of the other has an ee of 40% (70% − 30%). Enantiomeric excess is defined as the absolute difference between the mole fraction of each enantiomer: where In practice, it is most often expressed as a percent enantiomeric excess.
1998 Winter OlympicsThe 1998 Winter Olympics, officially known as the XVIII Olympic Winter Games and commonly known as Nagano 1998 (長野1998), was a winter multi-sport event held from 7 to 22 February 1998, mainly in Nagano, Japan, with some events taking place in the nearby mountain communities of Hakuba, Karuizawa, Nozawa Onsen, and Yamanouchi. The city of Nagano had previously been a candidate to host the 1940 Winter Olympics (which were later cancelled), as well as the 1972 Winter Olympics, but had been eliminated at the national level by Sapporo on both occasions.