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Optical and isomers are compounds which contain the same number and kinds of atoms, and bonds (ie the connectivity between atoms is the same), and different spatial arrangements of the atoms, but which have non-super imposable mirror images. Each non-super imposable mirror image structure is called an enantiomer. Optical isomers get their name because the plane – polarized light that is passed through a sample of a pure enantiomers is rotated. The planeis rotated in the opposite direction but with the same magnitude when plane- polarized light is passed through a pure sample containing the other enantiomer of a pair. A solution of one enantiomer rotates the plane of polrisation in a clockwise direction. This enantiomer is known as the (+) form. A solution of the other enantiomer rotales the plane of polarisation in an anti-clockwise direction. This enantiomer is known as (-) form.

 If the solution are equally  concentrated the amount of rototation caused by the two isomers is exactly the same , but in opposite directions. When optically active substance are made in the lab, they  often occurs as a 50/50 mixture of the two enantiopmers. This is known as a racemic mixture or racemate. It has no effect on plane polarised light.

Which of the following have the same rates of reaction ? 

(a) Reaction of (+) and (-) enantiomers with a chiral reagent.

(b) Reaction of diastereomers with a chiral reagent .

(c) Reaction of (+) and (-) enantiomers with an achiral reagent.

(d) Reaction of diastereomers with an achiral reagent.

1 Answer

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The transition state of the reaction of (+) and (-) enantiomers with an achiral regent being mirror images have the same energy of activation .
Hence (+) and (-) enantiomers react at the same rate.
So, Reaction of (+) and (-) enantiomers with an achiral reagent.
Hence c is the correct answer.
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