Organic Chemistry

Organic Chemistry - Ch 11 564 Daley & DaleyH 3 CHCH 3 CH 2SiHCH 3 CH 2ClSiCH 3(R)-Ethyl methyl phenyl silane(S)-Ethyl methyl silyl chlorideAnother possible stereocenter atom is nitrogen. Nitrogen formsamines that are derivatives of ammonia (NH 3 ) in which carboncontaininggroups replace one or more of the hydrogens. For example,ethylmethylamine has four different groups around the nitrogen: anethyl group, a methyl group, a hydrogen, and an electron pair.Because the geometry of this molecule is nearly tetrahedral,ethylmethylamine should be an asymmetric molecule with nitrogen asits stereocenter.NCHN3CHHH3CH 3 CH 2CH 2 CH 3Amine inversion flipsthe groups about theamine nitrogen fromone enantiomer to theother.A pair of enantiomers should exist, but they don't because a processcalled amine inversion prevent them from being separated. If youcompare the amine structure to an umbrella, then amine inversion issimilar to an umbrella turning inside out in the wind. At roomtemperature, this inversion process proceeds so rapidly that resolutionof the enantiomers is impossible.CH 3CH 3 CH 2NHCH 3 CH 2CH 3NHNitrogen is a stereocenter when ammonia forms derivativeswith cyclic structures and bulky groups. In these cases, inversion doesnot occur making it possible to separate the enantiomers. Some stericarrangements of the atoms within a compound also make aminewww.ochem4free.com 5 July 2005