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chapter5 - 5-5- Chiralityand ChiralityChapter 5Chapter...

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Unformatted text preview: 5-5-1StereoisomerismStereoisomerismand Chiralityand ChiralityChapter 5Chapter 55-5-2IsomersIsomers◆Isomers:Isomers:different compounds with the same molecular formula◆Constitutional isomers:Constitutional isomers:isomers with a different connectivity◆Stereoisomers:Stereoisomers:isomers with the same connectivity but a different orientation of their atoms in space5-5-3ChiralityChirality◆Chiral:Chiral:from the Greek, cheir, hand•an object that is not superposable on its mirror image◆Achiral:Achiral:an object that lacks chirality; one that lacks handedness•an achiral object has at least one element of symmetry•plane 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 half•center 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 Symmetry◆Symmetry in objectsSymmetry in objects5-5-5Elements of SymmetryElements of Symmetry◆Plane of symmetry (cont’d)HOOHmirrorplane5-5-6Chiral CenterChiral Center◆The most common (but not the only) cause of chirality in organic molecules is a tetrahedral atom, most commonly carbon, bonded to four different groups◆A carbon with four different groups bonded to it is called a chiral centerchiral center•all chiral centers are stereocenters, but not all stereocenters are chiral centers (see Figure 3.5)◆Enantiomers:Enantiomers:stereoisomers that are nonsuperposable mirror images•refers to the relationship between pairs of objects5-5-7EnantiomersEnantiomers◆2-Butanol•has one chiral center•here are four different representations for one enantiomer•using (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)5-5-8EnantiomersEnantiomers◆The enantiomers of lactic acid•drawn in two different representationsCCHOCH3HOHOCCOHCH3HOOHOHOHOOHHOO5-5-9EnantiomersEnantiomers◆2-ChlorobutaneCH3CHCH2CH3ClClHClH5-5-1010EnantiomersEnantiomers◆3-ChlorocyclohexeneClCl5-5-1111EnantiomersEnantiomers◆A nitrogen chiral centerNCH2CH3H3CNCH3CH3CH2A pair of enantiomers++5-5-1212R,SR,SConventionConvention◆Priority 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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chapter5 - 5-5- Chiralityand ChiralityChapter 5Chapter...

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