Home >
Community >
What is the relationship between configuration & optical rotation?
Upvote
23
Downvote
+ Stereochemistry
Posted by
Nwankwo Ekene
What is the relationship between configuration & optical rotation?
There is no general correlation between the the rectus (R) and sinister (S) prefixes and dextro/levorotation. In some cases the (R)-enantiomer is the dextrorotary enantiomer (as in the case of D-alanine), and in other cases the (R)-enantiomer is the levorotary enantiomer (as in the case of L-cysteine). The relationship can only be determined on a case-by-case basis with experimental measurements or detailed computer modeling.
For a really detailed explanation of exactly how chiral molecules rotate planes of polarized light, I recommend you check out this physics post, but to answer your other question, no it doesn't make sense for planes of polarized light to rotate according the Cahn–Ingold–Prelog Priority Rules. This system only takes into consideration the atomic number and number of bonds to atoms of a higher atomic number. Even though $\ce{-Cl}$ might rank higher than $\ce{-C(CH)3}$, wouldn't it make sense for the two groups to have different effects on rotation, in the cases of both direction and magnitude? This is why dextro/levorotation must be determined experimentally.
There is no general correlation between the the rectus (R) and sinister (S) prefixes and dextro/levorotation. In some cases the (R)-enantiomer is the dextrorotary enantiomer (as in the case of D-alanine), and in other cases the (R)-enantiomer is the levorotary enantiomer (as in the case of L-cysteine). The relationship can only be determined on a case-by-case basis with experimental measurements or detailed computer modeling.
For a really detailed explanation of exactly how chiral molecules rotate planes of polarized light, I recommend you check out this physics post, but to answer your other question, no it doesn't make sense for planes of polarized light to rotate according the Cahn–Ingold–Prelog Priority Rules. This system only takes into consideration the atomic number and number of bonds to atoms of a higher atomic number. Even though $\ce{-Cl}$ might rank higher than $\ce{-C(CH)3}$, wouldn't it make sense for the two groups to have different effects on rotation, in the cases of both direction and magnitude? This is why dextro/levorotation must be determined experimentally.
There is no general correlation between the the rectus (R) and sinister (S) prefixes and dextro/levorotation. In some cases the (R)-enantiomer is the dextrorotary enantiomer (as in the case of D-alanine), and in other cases the (R)-enantiomer is the levorotary enantiomer (as in the case of L-cysteine). The relationship can only be determined on a case-by-case basis with experimental measurements or detailed computer modeling.
For a really detailed explanation of exactly how chiral molecules rotate planes of polarized light, I recommend you check out this physics post, but to answer your other question, no it doesn't make sense for planes of polarized light to rotate according the Cahn–Ingold–Prelog Priority Rules. This system only takes into consideration the atomic number and number of bonds to atoms of a higher atomic number. Even though $\ce{-Cl}$ might rank higher than $\ce{-C(CH)3}$, wouldn't it make sense for the two groups to have different effects on rotation, in the cases of both direction and magnitude? This is why dextro/levorotation must be determined experimentally.
There is no general correlation between the the rectus (R) and sinister (S) prefixes and dextro/levorotation. In some cases the (R)-enantiomer is the dextrorotary enantiomer (as in the case of D-alanine), and in other cases the (R)-enantiomer is the levorotary enantiomer (as in the case of L-cysteine). The relationship can only be determined on a case-by-case basis with experimental measurements or detailed computer modeling.
For a really detailed explanation of exactly how chiral molecules rotate planes of polarized light, I recommend you check out this physics post, but to answer your other question, no it doesn't make sense for planes of polarized light to rotate according the Cahn–Ingold–Prelog Priority Rules. This system only takes into consideration the atomic number and number of bonds to atoms of a higher atomic number. Even though $\ce{-Cl}$ might rank higher than $\ce{-C(CH)3}$, wouldn't it make sense for the two groups to have different effects on rotation, in the cases of both direction and magnitude? This is why dextro/levorotation must be determined experimentally.
More
VOTE