Chirality and Isomers Flashcards
What are isomers?
Molecules that have the same molecular formula but a different arrangement of atoms in space
What is the difference between constitutional and stereo isomers?
constitutional (structural)= the atoms in the molecule are arranged in different orders
stereo= the atoms in the molecule are arranged in the same order, but in different 3 dimensional orientations
Do constitutional isomers have different properties?
Yes, they have different physical and chemical properties
What are cis/trans isomers?
Depending on whether the substituents of highest priority (based on the lowest atomic number) at eachend of the double bond are next to or opposite each other there are different isomers
cis isomers are on the same side, trans are on opposite sides
What are E and Z isomers?
The E,Z system must be used for tri and tetra substituted alkenes
to assign an E,Z configuration, you must first assign a priority to the substituents on each side of the double bonds
E isomers are on opposite sides, Z isomers are on the same side
What is a chiral object?
When something is chiral it does not match it’s reflection, achiral objects, are identical to their reflection
What is the structure of a chiral molecule?
A chiral structure has to have a 3 dimensional structure
- as soon as there are 4 different constituents, we have a chiral molecule
- if a molecule has 3 or 2 substituents it is achiral
What is a stereogenic centre?
Many chiral molecules contain a chiral centre called a stereogenic centre
What are enantiomers? + an example?
Stereoisomers that are mirror images of one another are enantiomers
entantiomers do not differ in physical characteristics, yet interact differently with polarized light and with stereospecific environments
EG: Lactic acid = 2-Hydroxypropanic acid
How to label/name enantiomers
the R and S labels are used to differentiate
- Locate the stereogenic centre and identify each 4 substituents
- assign a priority 1-4 to each substituent
- orient the lowest priority group away from you, the remaining 3 groups then project towards you
- look at the molecules so that group 4 points away and count the groups from 1-3
- if you have to read clockwise it is an R structure
- if you have to read anticlockwise it is an S structure
How to figure out how many stereoisomers are possible?
For molecules with “n” stereocentres, 2 to the power of “n” stereoisomers are possible
What are distereoisomers?
stereoisomers that are not mirror images and cannot be super imposed
What are enzymes in terms of steroisomerism?
Enzymes are chiral strucutres which only produce /react with substances that match their stereoisomer qualities
What are meso compounds?
Compunds with many chiral centres that are achiral
