Chapter 5 Flashcards
(18 cards)
What is an enantiomer?
a pair of non-superimposable
(can’t accurately draw structure from mirro-image) mirror-image molecules
what properties do enantiomers share?
boiling point, melting point, density
When do enantiomers occur?
when a tetrahedral is bonded to four different substituents(at least one can’t be H)
How can you predict when a given molecule is chiral or not?
a molecule is not chiral if it has a plane of symmetry
if it has a plane of symmetry in any conformation it must be ACHIRAL
if there is no carbon atom in a molecule bonded to four different groups is it achiral or chiral?
achiral
what are Cahn-ingold-prelog rules used for?
used to rank the four groups attached to the chirality center and then looks at the handedness with which those groups are attached
What are 3 rules of cahn-ingold-prelog?
- look at the four atoms directly attached to the chirality center, and rank them according to the atomic number
- if a decision can’t be reached by ranking the first atoms in the substituent, look at the second, third, or fourth atoms away from the chirality center until the first difference is found
- multiple-bonded atoms are equivalent to the same number of single-bonded atoms
are atoms with higher or lower atomic number ranked higher?
higher atomic number=higher ranking
does a double or triple bond give a group higher priority?
no!
is R configuration clockwise or counterclockwise?
clockwise
what is a molecule with more than one chirality center called?
diastereomer
How to determine the number of stereoisomers based on number of chirality center?
one chirality center=two stereoisomers, and a molecule with “n” chirality centers can have up to 2^n stereoisomers
What is a key difference between enantiomers and diastereomers?
enantiomers have opposite configuration at ALL chirality centers and are mirror-images, whereas diastereomers have opposite configuration at only SOME(ONE OR MORE) chirality centers and are not mirror-images
what is a meso compound?
a structure that is achiral(contains a plane of symmetry) but still contains chirality centers
What is Racemic Mixture?
a 50:50 mixture of chiral enantiomers that are denoted by +- or d, l to indicate an equal mixture of dextrotatory and levorotatory forms
do racemic mixtures show optical rotation? why or why not?
no beecause the + rotation from one enantiomer exactly cancels out the - rotation from the other
what 3 types of consitutional isomers are there?
skeletal(different carbon skeletons), functional(different functional groups), positional(different position of functional groups)
