diastereomers are species with different arrangements of atoms but having no structural differences and which are not non-superposable mirror-images of each other.
diastereomers are species with different arrangements of atoms but having no structural differences and which are not non-superposable mirror-images of each other.
species with different arrangements of atoms but having no structural differences and which are not non-superposable mirror-images of each other?
diastereomers
stereoisomers have the same bond connectivity but different geometries. two broad classes of stereoisomers are recognized: enantiomers and diastereomers. enantiomers are non-superposable mirror-images of each other. diastereomers are not. enantiomers always contain chiral centers. some diastereomers are chiral and some are not. another type of isomer, conformational isomers (conformers), may be rotamers, diastereomers, or enantiomers depending on the compound. for example, ortho- position-locked biphenyl systems have enantiomers.









































e/z isomers, which have restricted rotation at a double bond, are configurational isomers. they are classified as diastereomers. e/z notation depicts absolute stereochemistry, which is an unambiguous descriptor based on cip priorities.
isomer
an asymmetric carbon atom is one which has bonds with four "different" atoms or groups, so that these bonds can be arranged in two different ways which are not superposable. most compounds that contain one or more asymmetric carbon (or other element with a tetrahedral geometry) atoms show enantiomerism, but this is not always true. compounds that contain two or more asymmetric carbon atoms but have a plane of symmetry with respect to the whole molecule are known as "meso" compounds. a "meso" compound does not have a mirror image stereoisomer because it is its own mirror image (i.e., it and its mirror image are the same molecule). for instance, "meso" tartaric acid (shown on the right) has two asymmetric carbon atoms, but it does not exhibit enantiomerism because each of the two halves of the molecule is equal and opposite to the other and thus is superposable on its geometric mirror image. conversely, there exist forms of chirality that do not require individual asymmetric atoms. in fact, there are four distinct types of chirality: central, axial, planar, and helical chirality. having an enantiomer by virtue of an asymmetric carbon atom represents the most common type of central chirality. the other three types of chirality do not involve asymmetric carbon atoms, and even central chirality does not require the center of chirality to be located at a carbon or any other atom. consequently, while the presence of an asymmetric carbon atom is a convenient characteristic to look for when determining whether a molecule will have an enantiomer, it is neither sufficient nor necessary as a criterion.
enantiomer