stereroisomerism -...
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STEREROISOMERISM20.6
Tuesday, January 24, 2012
Stereoisomers
have the same molecular formula and sequence of bonded atoms (constitution), but that differ only in the three-dimensional orientations of their atoms in space
Tuesday, January 24, 2012
Tuesday, January 24, 2012
EnantiomersStereoisomers that are related to each other by a reflection: They are mirror images of each other, which are non-superimposable.
Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light
Tuesday, January 24, 2012
Cis or Trans Isomers Such isomers contain double bonds, which cannot rotate, but they can also arise from ring structures.
The terms cis and trans are from Latin, in which cis means "on the same side" and trans means "on the other side"
Tuesday, January 24, 2012
Tuesday, January 24, 2012
Cis Trans PropertiesTrans-alkenes, which are less polar and more symmetrical, have lower boiling points and higher melting points, and cis-alkenes, which are generally more polar and less symmetrical, have higher boiling points and lower melting points.
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Chemical Properties Primarily there are little to no differences in the chemical properties of isomers. Some exceptions to this do occur.
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Cyclic Cis TransWhen two substituents on a ring point to the same face, they are cis. When the two substituents point to opposite faces, they are trans. Like the cases of cis-trans isomerism in alkenes, these isomers have the same atomic connectivities but differ in their spatial arrangement of atoms. Hence, they are stereoisomers.
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Cyclic Cis Trans Examples
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Chiral Center
A chiral center is defined as an atom that is bonded to four different chemical species, allowing for optical isomerism.
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom.
Tuesday, January 24, 2012
Optical Isomers
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Chiral compounds rotate plane polarized light. Each enantiomer will rotate the light in a different sense, clockwise or counterclockwise. Molecules that do this are said to be optically active.
Tuesday, January 24, 2012