Question | Answer | answer cont. |
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 |
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 |
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 | |
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 | |
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 | |
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). | |
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 | |
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 |
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 | |
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 |