chapter5 - 5-5-1StereoisomerismStereoisomerismand...

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Unformatted text preview: 5-5-1StereoisomerismStereoisomerismand Chiralityand ChiralityChapter 5Chapter 55-5-2IsomersIsomersIsomers:Isomers:different compounds with the same molecular formulaConstitutional isomers:Constitutional isomers:isomers with a different connectivityStereoisomers:Stereoisomers:isomers with the same connectivity but a different orientation of their atoms in space5-5-3ChiralityChiralityChiral:Chiral:from the Greek, cheir, handan object that is not superposable on its mirror imageAchiral:Achiral:an object that lacks chirality; one that lacks handednessan achiral object has at least one element of symmetryplane of symmetry:plane of symmetry:an imaginary plane passing through an object dividing it so that one half is the mirror image of the other halfcenter of symmetry:center of symmetry:a point so situated that identical components are located on opposite sides and equidistant from that point along the axis passing through it5-5-4Elements of SymmetryElements of SymmetrySymmetry in objectsSymmetry in objects5-5-5Elements of SymmetryElements of SymmetryPlane of symmetry (contd)HOOHmirrorplane5-5-6Chiral CenterChiral CenterThe most common (but not the only) cause of chirality in organic molecules is a tetrahedral atom, most commonly carbon, bonded to four different groupsA carbon with four different groups bonded to it is called a chiral centerchiral centerall chiral centers are stereocenters, but not all stereocenters are chiral centers (see Figure 3.5)Enantiomers:Enantiomers:stereoisomers that are nonsuperposable mirror imagesrefers to the relationship between pairs of objects5-5-7EnantiomersEnantiomers2-Butanolhas one chiral centerhere are four different representations for one enantiomerusing (4) as a model, here are two different representations for the enantiomer of (4)OHCH3CCH2CH3HOHCH3CCH2CH3HHOHOH(1)(2)(3)(4)OH(4)OHOHrepresentations for theenantiomer of (4)5-5-8EnantiomersEnantiomersThe enantiomers of lactic aciddrawn in two different representationsCCHOCH3HOHOCCOHCH3HOOHOHOHOOHHOO5-5-9EnantiomersEnantiomers2-ChlorobutaneCH3CHCH2CH3ClClHClH5-5-1010EnantiomersEnantiomers3-ChlorocyclohexeneClCl5-5-1111EnantiomersEnantiomersA nitrogen chiral centerNCH2CH3H3CNCH3CH3CH2A pair of enantiomers++5-5-1212R,SR,SConventionConventionPriority rules1. Each atom bonded to the chiral center is assigned a priority based on atomic number; the higher the atomic number, the higher the priority2. If priority cannot be assigned per the atoms bonded to the chiral center, look to the next set of atoms; priority is assigned at the first point of difference(53)(35)(17)(16)(8)(7)(6)(1)Increasing priority-H -CH3 -NH2 -OH -SH -Cl -Br -IIncreasing priority(8)(7)(6)(1)- CH2-OH-CH2-NH2- CH2-CH3- CH2-H5-5-1313R,S ConventionR,S Convention3. Atoms participating in a double or triple bond areconsidered to be bonded to an equivalent number of similar atoms by single bonds-CH=CH2O-CHC CHOHCCOC-CH-CH2CC C HCCCCis treated asis treated asis treated as5-...
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This note was uploaded on 09/19/2011 for the course CHM 261 taught by Professor Wenthold during the Spring '11 term at Purdue University-West Lafayette.

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chapter5 - 5-5-1StereoisomerismStereoisomerismand...

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