Organic Chemistry

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Organic Chemistry - Ch 11 563 Daley & DaleyHHOOC OOHHCOOHCH 3COOHCH 3OHH OHCH 2 CH 3 HO H +HO HCH 2 CH 3COOHydrolysis of the (S)-2-butyl tartrate gives (S)-2-butanol, completingthe resolution of the enantiomers.HCH 3OCOOO CCH 3OHH OHCH 2 CH 3 H OHH OH +HO HHO HCH 2 CH 3COOCOOHExercise 11.9The same concept of resolution of enantiomers also applies to amines.An amine reacts with a carboxylic acid to produce a salt.R'COOH +CarboxylicacidRNH 2AmineR'COO NH 3 RSaltUsing (+)-tartaric acid, accomplish the resolution of 2-aminobutane.Draw the diastereomeric salts that result from this reaction.11.8 Stereocenters Other than CarbonAlthough carbon is the most commonly found stereocenter in amolecule, a number of other atoms can be stereocenters, too. One ofthese atoms is silicon. Silicon forms the same sort of tetrahedralstructure as carbon; thus, a silicon atom with four different groupsbonded to it can be asymmetric, and indeed there are many examplesof compounds with silicon stereocenters.www.ochem4free.com 5 July 2005
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
Page 1 and 2: Richard F. Daley and Sally J. Daley
Page 3 and 4: Organic Chemistry - Ch 11 532 Daley
Page 38: Organic Chemistry - Ch 11 567 Daley

Organic Chemistry

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