flashcards on achiral, chiral, and stereomolecules
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| What is Chiral/Achiral How do you distinguish between the two? | Chiral: mirror images of a molecule are not superimposable, doesn't always have a stereocenter, NO PLANE OF SYMMETRY Achiral: mirror images of a molecule are superimposable, PLANE OF SYMMETRY | Test superimposability or see if it has a plane of symmetry
all planar molecules are achiral
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| what are enantiomers, diastereomers and meso compounds | enantiomers: must be chiral, mirror image pairs diastereomers: not superimposable, not mirror images meso compounds: has two or more stereocenters but is superimposable with mirror image all meso compounds are achiral | meso compounds can be spotted due to their internal plane of symmetry
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| How do you identify stereocenters in a chiral molecule? what is a racemic mixture? | it is attached to 4 DIFFERENT groups a racemic mixture: A + its enantiomer = 50/50 |
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| What is the difference between identical, structural isomers, conformers, and stereoisomers | identical: exactly the same structural: same molecular formula, different structural formula conformers: different rotations of same molecular structure stereoisomers: atoms connected same, different spatial structure, ie. diastereomers and enant |
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| Cahn, Ingold, Prelog rules to assign substituents | 1. higher atomic number = higher priority and vice versa 2.if same A.N., go down chain to first point of difference, the one w attached to more things besides H, is higher priority 3.double and triple bonds treated as single bonds and expanded |
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| What is one way to assign R/S? | Version 1 1.rank substituents by priority 2.rotate until lowest, usually H, is farthest away 3.determine if the ranking progression is clockwise(R) or counter clockwise(S). |
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| What is the other way to assign R/S? | Version 2 1. rank substituents by priority 2. place thumb along stereocenter bond 3. see which hand, when curled gives 1,2,3 progression. Right means R, left means S |
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| how do you compare relationships in more complex structures? | use R/S if all the r's switch to s's and vice versa, it's an enantiomer if some r's switch to s's or vice versa, its a diastereomer | if you invert a stereocenter, the R/s switches
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| what happens with halgenation of different parts of an alkane | if you halogenate a substituent, it remains active as long as the stereocenter is left intact halogenation of a stereocenter leads to a racemic mixture |
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| based on the relationship between two stereoisomers as diastereomers or enantiomers, what will their physical properties be like? | bond length increases and strength decreases as you move down the pd table when bonded to a halogen bc of the mismatch | but enantiomers, because they are the similar , mirror images, have the same properties. and diastereomers, because they are different, not superimposable or mirror images, have different properties
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