Optical Isomers Flashcards
What is an enantiomer
What is an diasteriomer
Carbon with 4 diff groups all Chiral centres changed, same physical properties but they rotate plane of polarized light in diff directions
Carbon with 4 diff groups more than one but not all Chiral centres changed, diff chemical/ physical properties
What is the sign of alpha in the R enantiomaer
What about S
-
+
If it’s a 50:50 race mix mixture does is have optical rotation?
No it doesn’t rotate the plane of polarized light
How do you know the max amount of isomers for a single compund
2^n
If 2 chiral centres, 4 diff types of isomers of that one compound
R,R
S,S
R,S
S,R
If something is meso what does this mean
It has an internal mirror plane
Meaning it’s optically inactive and achiral
It’s alpha value is 0
What is polarimetry and what does it depend on
Measuring the observed rotation (alpha)
The sign and magnitude of alpha depends on structure, concentration, and path length
What is the equation for calculating specific rotation? [alpha]
= (observed alpha/length of the cell in dm x [] in g/ml)
If you have a mix or samples and the specific rotation is - what does this mean
If it was zero what would this mean
The R enantiomer is in excess
The mixture is a 50:50 mix
How do we find % optical purity of a sample
What does this mean
100x alpha of the mix sample/ alpha of the pure sample (the one in excess)
If 50% this means the samole has 50% more of R than S
How do you find % enantiomeric excess
Two ways
%ee= % optical purity
Or
%ee= % R - %S
How do you find what percent of a specific isomer I present in a mixture?
Use these equations if %ee= 50
%50= %R-%S
%R + %S = 100%
Isolate for S plug into second equation
R= 75 S= 25
