Organic Chemistry

Organic Chemistry - Ch 11 537 Daley & Daleyc) Spiro[4.3]octaned) trans-DecalinSample Solutionb) 1-Methylcyclohexanol has one plane of symmetry that bisects the —OH and —CH 3 groups on C-1 as well as C-1 and C-4.OHPlane of symmetryCH 3An enantiomer is one ofa pair ofnonsuperimposiblemirror imagemolecules.Molecular asymmetryis the result of amolecule’s shape.An organic molecule without a plane of symmetry or center ofsymmetry is asymmetric. A characteristic of all asymmetric moleculesis that they possess chirality. That is, for that molecule there exists anonsuperimposible mirror image molecule. All chiral, or asymmetric,molecules occur in pairs with a “right hand” and a “left hand”molecule. Each member of the pair is called an enantiomer. Forexample, there are two enantiomers of 2,3-pentadiene. To confirmthis, make a model of Figure 11.5 and then another of its mirrorimage. As you examine these two stereoisomers, note that they do nothave a plane of symmetry and that you cannot superimpose onemolecule upon the other. Their asymmetry is due to their shape, ormolecular asymmetry.HCH 3CCCHCH 3Figure 11.5. 2,3-Pentadiene is an example of a chiral molecule that does not have aplane or center of symmetry.A stereogenic center isa specific atom in amolecule that isresponsible for some orall of the molecularasymmetry.Although all chiral molecules have molecular asymmetry,many asymmetric molecules have a stereogenic center or, morespecifically, an asymmetric carbon atom. An asymmetric carbon atomis often called a stereocenter. An asymmetric carbon atom is bonded tofour nonequivalent substituents. This asymmetry is a propertyallowed by the tetrahedral structure of a carbon atom.www.ochem4free.com 5 July 2005