The absolute configuration at the chirality center in the diol obtained by dihydroxylation of t r a n s -2-butene is to be determined when one of the chirality center has ( R ) -configuration. Concept introduction: The dihydroxylation is the addition of two hydroxyl groups to the double bond of an alkene to form a 1,2-diol . The dihydroxylation of alkene is a s y n - type of addition as both hydroxyl groups add to the double bond from the same side. The osmium tetroxide reacts with alkene and forms a cyclic osmate ester. In the presence of an oxidizing agent, this ester forms a diol. The stereochemistry of chiral center is predicted by assigning the absolute configuration to the molecule. The absolute conjugation can be determined by assigning priority to the groups bonded to chirality center. The priority order is decided by Cahn-Ingold-Prelog priority rules. If the order of priority of groups bonded to chirality center preceding 1 → 2 → 3 is clockwise, then the absolute configuration is ( R ) , and if it is counterclockwise, then the absolute configuration is ( S ) . The c i s alkene, on dihydroxylation, forms the meso compound in which both carbon atoms bonded to hydroxyl group have opposite absolute configuration. The t r a n s alkene, on dihydroxylation, forms a racemic mixture and both the carbon atoms in a diol that are bonded to hydroxyl group have same absolute configuration.

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Chapter 16.5, Problem 6P

Interpretation Introduction

Interpretation:

The absolute configuration at the chirality center in the diol obtained by dihydroxylation of trans-2-butene is to be determined when one of the chirality center has (R)-configuration.

Concept introduction:

The dihydroxylation is the addition of two hydroxyl groups to the double bond of an alkene to form a 1,2-diol.

The dihydroxylation of alkene is a syn- type of addition as both hydroxyl groups add to the double bond from the same side.

The osmium tetroxide reacts with alkene and forms a cyclic osmate ester. In the presence of an oxidizing agent, this ester forms a diol.

The stereochemistry of chiral center is predicted by assigning the absolute configuration to the molecule.

The absolute conjugation can be determined by assigning priority to the groups bonded to chirality center.

The priority order is decided by Cahn-Ingold-Prelog priority rules. If the order of priority of groups bonded to chirality center preceding 1→2→3 is clockwise, then the absolute configuration is (R), and if it is counterclockwise, then the absolute configuration is (S).

The cis alkene, on dihydroxylation, forms the meso compound in which both carbon atoms bonded to hydroxyl group have opposite absolute configuration.

The trans alkene, on dihydroxylation, forms a racemic mixture and both the carbon atoms in a diol that are bonded to hydroxyl group have same absolute configuration.

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