Organic Chemistry

Organic Chemistry - Ch 11 565 Daley & Daleyinversion impossible. For example, 1-azabicyclo[3.2.1]octane cannotundergo amine inversion, thus allowing the enantiomers to beseparated.N1-Azabicyclo[3.2.1]octanePhosphorus is in the same group on the periodic table asnitrogen and, like nitrogen, it also forms trigonal pyramidalstructures. However, unlike the amines formed by nitrogen,phosphines do not undergo rapid inversion. Thus, phosphorus is astereocenter that can form a number of optically active phosphines.For example, ethyl methyl phenyl phosphine is asymmetric and hasbeen resolved.••PCH 3CH 2 CH 3Ethyl methyl phenyl phosphineWhen sulfur has three different substituents, it also formscompounds that are asymmetric. The rate of inversion for asymmetricsulfur compounds is quite slow, allowing for ready resolution of theenantiomers. An example of a compound with sulfur as thestereocenter is a dialkyl sulfoxide such as the ethyl methyl sulfoxideshown below.••CH 3CH 3 CH 2SOEthyl methyl sulfoxideThe Cahn-Ingold-Prelog priority rules specify the absoluteconfiguration of any of these centers. These rules assign the unsharedpair of electrons a lower priority than hydrogen. Application of thesepriority rules to ethyl methyl sulfoxide is shown below.www.ochem4free.com 5 July 2005