9) Unit 2 - Sterochemistry Flashcards
What is an isomer
molecules that have the same molecular formula but differ in the way their atoms are arranged
what are the 2 types of isomers
- structural isomers
* stereoisomers
describe a structural isomer
atoms are bonded together in a different order in each isomer
describe stereoisomer
atoms are bonded in the same order, but the arrangement of atoms in space is different for each isomer
Name the two types of stereoisomers
- geometric
* optical
when does geometric isomerism occur
- in molecules with a c=c bond, with each carbon having 2 different groups attached to it
- in cycloalkanes
what does cis and trans mean in geometric isomers with c=c bonding
cis = when two groups are on the same side trans = when groups are on opposite sides
what does cis and trans mean in geometric isomers with saturated rings (cycloalkanes)
cis = when 2 groups are on the same side of the plane trans = when 2 groups are on opposite sides of the plane
what are optical isomers and where do they occur
- asymmetrical molecules that are non-superimposable mirror images of each other
- exist in compounds with a chiral carbon atom (1 carbon bonded to 4 different groups)
How are optical isomers different
optical isomers are identical in every physical property except their effect on plane polarised light
They can be identified as R or S.
how is light deflected in a:
100% R-isomer
100% to the right
how is light deflected in a:
100% S-isomer
!00% to the left
how is light reflected in a:
70% R and 30% S isomer
40% to the right
How is light deflected in a:
20% R and 80% S isomer
60% to the left
•How is light deflected in a:
50% R and 50% S isomer
•And what is this called
- there is no deflection
* this mixture is called a race mixture
