how we check given carbon is pseudo chiral?................. no useless answer plz
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The traditional name for a tetrahedrally coordinated carbon atom bondedto four differententities, Two and only two of which have the same constitution but opposite chirality sense .This is the reason how we can know given carbon is pseudo chiral .
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An atom is said to be pseudochiral if any change in the configuration (spatial arrangement) of adjascent atoms brings a change in the chirality of atom under investigation.
Let us discuss it in 2,3,4-trichloropentane.
This molecule 2,3,4-trichloropentane has three chiral carbon on C2 , C3 and C4. But the carbon C3 is conditionally chiral .Note the Carbon C2 and C4 is chiral in all conditions as they have 4 different groups connecting the carbon namely Chloro, Methyl,Hydrogen and 1,2 Dichloropropyl groups. It is represented in given figure. On this basis it should have 4 stereoisomers with the notations (2R,4R) ,(2S,4S), and (2R,4S) or (2S,4R).
Note that (2R,4S) or (2S,4R) have two chiral carbon with opposite configuration ie.they must be optically inactive with POS and COS. For (2R,4R) and (2S,4S) the C3 is achiral as C3 has one H, One F, and two similar (R)-1-Chloroethyl groups.
But both (2R,4R) and (2S,4S) are optically active and both are enantiomeric pair.For (2R,4S) and (2S,4R) the C3 is chiral as C3 has one H, One F, and one (R)-1-Chloroethyl group and one (S)-1-Chloroethyl group. Both (2R,4S) and (2S,4S) are not identical to each other.
Here C3 Carbon is the pseudochiral carbon.On the basis of RS naming convention where R has greater priority than S. Now C3 may be (r) or (s) as it has 4 different groups: F as 1, (R)-1-Chloroethyl group as 2,(s)-1-Chloroethyl group as 3 and H as 4th priority group.
Finally we have only 4 stereoisomers (2R,4R) ,(2S,4S), (2R,3r,4S) and (2R,3s,4S). The stereoisomers (2R,3r,4S) and (2R,3s,4S) are diastereoisomer to each other.
Let us discuss it in 2,3,4-trichloropentane.
This molecule 2,3,4-trichloropentane has three chiral carbon on C2 , C3 and C4. But the carbon C3 is conditionally chiral .Note the Carbon C2 and C4 is chiral in all conditions as they have 4 different groups connecting the carbon namely Chloro, Methyl,Hydrogen and 1,2 Dichloropropyl groups. It is represented in given figure. On this basis it should have 4 stereoisomers with the notations (2R,4R) ,(2S,4S), and (2R,4S) or (2S,4R).
Note that (2R,4S) or (2S,4R) have two chiral carbon with opposite configuration ie.they must be optically inactive with POS and COS. For (2R,4R) and (2S,4S) the C3 is achiral as C3 has one H, One F, and two similar (R)-1-Chloroethyl groups.
But both (2R,4R) and (2S,4S) are optically active and both are enantiomeric pair.For (2R,4S) and (2S,4R) the C3 is chiral as C3 has one H, One F, and one (R)-1-Chloroethyl group and one (S)-1-Chloroethyl group. Both (2R,4S) and (2S,4S) are not identical to each other.
Here C3 Carbon is the pseudochiral carbon.On the basis of RS naming convention where R has greater priority than S. Now C3 may be (r) or (s) as it has 4 different groups: F as 1, (R)-1-Chloroethyl group as 2,(s)-1-Chloroethyl group as 3 and H as 4th priority group.
Finally we have only 4 stereoisomers (2R,4R) ,(2S,4S), (2R,3r,4S) and (2R,3s,4S). The stereoisomers (2R,3r,4S) and (2R,3s,4S) are diastereoisomer to each other.
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