The nadir (UK: /ËnÃ¦dÉªÉr/), (US: /ËneÉªdÉªÉr/) (from Arabic: ÙØ¸ÙØ±ââ / ALA-LC: naáºÄ«r, meaning counterpart) is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there.
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen preferentially to one of two faces of an unsaturated substrate molecule, such as an alkene or ketone.ne of these is in the asymmetric hydrogenation of N-unfunctionalized imines to give primary amines. Such species can be difficult to selectively reduce because they tend to exist in complex equilibria of imine and enamine tautomers, as well as (E) and (Z) isomers.
Punctuated equilibrium can be accommodated within the classical neo-Darwinian synthesis as an end-member of the spectrum of possible evolutionary events that lead to the appearance of new species. But it's not the only possible mode of speciation: it is one possible mode. There's no intrinsic reason that evolutionary change should occur only in small populations, and there's no evidence that populations that have undergone marked evolutionary change are any smaller than those that are stable.