Lecture 8 - Principles of Stereochemistry Flashcards
stereoisomerism:
compounds that have the same connectivity, but a different arrangement of atoms in space (e.g. E-Z/cis-trans alkene isomers)
two types of stereoisomerism:
enantiomers and diastereoisomers
how can you tell if something is achiral?
construct the mirror image of an object if the mirror image is congruent (i.e., superimposable) with the original object it is achiral (i.e. not chiral)
ONLY definition of chiral:
an object is chiral if it has a non-super impossible mirror image
only test to see if something is chiral:
checking if it has a imposable/non-imposable mirror image
achiral:
a molecule that has a superimposable mirror image
what sort of propert is chirality:
chirality is a symmetry property
how do we note chiral carbons [asymmetric centre]?
through an asterics [*] notation
asymmetric centre:
any *carbon with 4 DIFFERENT groups [but doesn’t have to be JUST carbon, can also be phosphorous]
many chiral molecules contain:
one or more asymmetric carbons
an asymmetric carbon is a type of…
… stereocentre
stereocentres [also known as a stereogenic atom]:
- an atom at which the interchange of two groups gives a stereoisomer
what relationship do ENANTIOMERS concern:
the relationship between only 2 molecules
molecules that have a non-superimposable (non-congruent) mirror image are:
chiral
molecules that are non-congruent mirror images of one another are defined as:
enantiomers
example of a macroscopic set of enantiomers:
our very own hands
the configuration of an asymmetric carbon can be specified using the:
Cahn-Ingold-Prelog Rules
Cahn-Ingold-Prelog Rules:
they are arranged into priorities using atomic number and viewed from opposite the low priority group
how do we view our asymmetric centres?
we must view our asymmetric centre from opposite the low priority group
where is the group of lowest priority always found?
the group of lowest priority is always away from the observer
S configuration:
(lowest priority is behind) and remaining priorities descend in counterclockwise order
R configuration:
(lowest priority is behind) and remaining priorities descend in clockwise order
a molecule with a plane of symmetry is never…
… chiral
what sort of bond should the low priority bond always lie on?
the lowest priority gourd should always be on a dotted fading bond
properties of enantiomers:
enantiomers share identical physical properties EXCEPT for their interaction with plane polarised light
a stereoisomer is named by:
indicating the configuration of each asymmetric carbon before the systematic name
enantiomers and plane-polarised light:
Enantiomers rotate plane-polarized light in equal, but opposite directions
The sign of optical rotation is unrelated to R and S configuration of a compound
