As a historical note, thalidomide was never approved for use in the United States. 66 0 obj<>stream
The stereocenters are labeled as R or S. Consider the diagram above on the left: a curved arrow is drawn counter-clockwise (c-cw) from the highest priority substituent (1) to the lowest priority substituent (4) in the S-configuration ("Sinister" → Latin= "left").
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Have questions or comments? A big thanku. Of the four bonds to the chiral center, the #4 priority is hydrogen. Which of the two ‘C’ groups is priority #2, the aldehyde or the CH, With our priorities assigned, we look next at the #4 priority group (the hydrogen) and see that it is pointed back away from us, into the plane of the page - thus step 4a from the procedure above applies. Rule 2: Interchanging any two ligands on the chiral center changes the absolute configuration at the chiral center. First manufactured by a German drug company and prescribed widely in Europe and Australia in the late 1950's as a sedative and remedy for morning sickness in pregnant women, thalidomide was soon implicated as the cause of devastating birth defects in babies born to women who had taken it. The first is 6,6'-dinitrobiphenyl-2,2'-dicarboxylic acid. Rule 2: Rotation of three ligands on the chiral center in either direction, keeping the remaining ligand in place, does not change the absolute configuration at the chiral center. Is it part of the game and how do you use it? For example, let’s go back to the 2-chlorobutane starting with the wedge chlorine: Chlorine is the first priority, then we have two carbons and a hydrogen which gets the lowest priority. So, one S beats N, O, F because it has a higher atomic number than the others individually. For example, the ethenyl group (CH2=CH) has higher priority than the ethyl group (CH3CH2). And that is why this is also known as the Absolute Configuration or most commonly referred to as the R and S system. Step 1 0000001246 00000 n
If you have a modeling kit use it as you read through this section and work the practice problems. So, we discussed the roles of priorities 1, 2, and 3 but what about the lowest priority? Multiple bonds are treated as if each bond of the multiple bond is bonded to a unique atom. 0000007090 00000 n
Carbon “b” is connected to one oxygen and one hydrogen. Option one.
Here, you leave the molecule as it is with the hydrogen pointing towards you. 0000004229 00000 n
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Step 2 - vertical option The only thing you have to do at the end is change the result from R to S or from S to R. In this case, the arrow goes counterclockwise but because the hydrogen is pointing towards us, we change the result from S to R. Of course, either approach should give the same result as this is the same molecule drawn differently. The racemic drug is Celexa. The arrow goes clockwise, however, the absolute configuration is S, because the hydrogen is pointing towards us. The operations that do change the absolute configuration at a chiral center in a Fischer projection can be summarized as two rules. The "right hand" and "left hand" nomenclature is used to name the enantiomers of a chiral compound. ���=�6���������D�s���Tԯ]���M�b)0��������8GD����������B�8�;az��z̪L�e�m��ir��_������Z���٠|-��j�lWv�M'.������4} First manufactured by a German drug company and prescribed widely in Europe and Australia in the late 1950's as a sedative and remedy for morning sickness in pregnant women, thalidomide was soon implicated as the cause of devastating birth defects in babies born to women who had taken it. Assigning R/S configuration to glyceraldehyde: Two priorities are easy: hydrogen, with an atomic number of 1, is the lowest (#4) priority, and the hydroxyl oxygen, with atomic number 8, is priority #1. For this, there is this simple yet such a useful trick making life a lot easier. Sometimes it happens that two or more atoms connected to the chiral center are the same and it is not possible to assign the priorities right away. 0000009364 00000 n
Swapping any two groups on a chiral center inverts its absolute configuration (, How to Determine the R and S configuration, Enantiomers Diastereomers the Same or Constitutional Isomers with Practice, Chirality and Enantiomers: Determine if Enantiomers or identical based on R and S Configuration, Fischer Projections with Practice Problems, Diastereomers: Determine the Relationship-Constitutional Isomers Enantiomers or Diastereomers, Enantiomeric Excess (ee): Percentage of Enantiomers from Specific Rotation with Practice Problems, Calculating Enantiomeric Excess from Optical Activity, Resolution of Enantiomers: Separate Enantiomers by Converting to Diastereomers.
In our molecule, we only have one carbon with four different groups and that is the one with the bromine and we are going to assign the absolute configuration of this chiral center. 0000003677 00000 n
Meso compounds have a) an even number asymmetric atoms of opposite configuration. 0000001326 00000 n
Its enantiomer, by definition, must be (S)-glyceraldehyde. Owing to its three bonds to oxygen, the carbon on the acid group takes priority #2, and the methyl group takes #3.
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