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What's the difference between using the R, S label for steriochemistry vs the +. - ?
quick sterochem question
- Thread starter ihatebluescrubs
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R and S can be found by looking at the molecular structure. +/- can only be found experimentally. However, if you know the optical orientation (+/-) of one molecule, then its enantiomer has the opposite sign.
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Assuming that it has one chiral center, otherwise things get more complicated
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French physicist used the Rotation of Light to distinguish between enantiomers using the + / - system.
An enantiomer that rotates plane-polarized light in the positive direction, or clockwise, is called dextrorotary [(+), or d-], while the enantiomer that rotates the light in the negative direction, or counterclockwise, is called levorotary [(-), or l-]. When both d- and l- isomers are present in equal amounts, the mixture is called a racemic mixture. DO not mix Recemic with Meso
Left rotation: (-) or l or levorotatory.
Right rotation: (+) or d or dextrorotatory.
Caution: (+) or (-) does NOT correspond to R/S configurations.
Caution: d and l is NOT the same as D and L. The upper case letters denote absolute configurations in sugars.
Absolute configuration is the (R) or (S) that's labeled on the chiral centers
Relative configuration used before the mid-1800s, people did not have an understanding of the tetrahedral carbon atom, so they did not have absolute configurations. Instead, they used the relative configurations of which way a compound rotates plane-polarized light.
An enantiomer that rotates plane-polarized light in the positive direction, or clockwise, is called dextrorotary [(+), or d-], while the enantiomer that rotates the light in the negative direction, or counterclockwise, is called levorotary [(-), or l-]. When both d- and l- isomers are present in equal amounts, the mixture is called a racemic mixture. DO not mix Recemic with Meso
Left rotation: (-) or l or levorotatory.
Right rotation: (+) or d or dextrorotatory.
Caution: (+) or (-) does NOT correspond to R/S configurations.
Caution: d and l is NOT the same as D and L. The upper case letters denote absolute configurations in sugars.
Absolute configuration is the (R) or (S) that's labeled on the chiral centers
Relative configuration used before the mid-1800s, people did not have an understanding of the tetrahedral carbon atom, so they did not have absolute configurations. Instead, they used the relative configurations of which way a compound rotates plane-polarized light.
