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Chapter 4: Problem 20

Draw all the possible isomers of threonine and assign \((R, S)\) nomenclature to each.

Short Answer

Expert verified
There are 4 possible isomers of threonine. Assigning (R, S) nomenclature to each depends on the arrangement of constituent groups around each chiral center.

Step by step solution

01

Understand Threonine Structure

Threonine is an alpha-amino acid with the chemical formula \(C_4H_9NO_3\). It is composed of a carboxyl group \(-COOH\), an amino group \(-NH2\), a side chain consisting of a hydroxyl group \(-OH\) and a methyl group \(-CH3\), and a single hydrogen atom \(-H\), all attached to a central carbon atom.
02

Generate Isomers

Each isomer should have a different arrangement of the side chain, amino, carboxyl group, and hydrogen around the carbon atom. There are 2 chiral centers (the alpha-carbon and the chiral carbon in the side chain), therefore, there are \(2^2 = 4\) isomers from these 2 chiral centers.
03

Assign (R, S) Nomenclature

Determine the priority of each group attached to a chiral carbon based on atomic number (higher atomic number = higher priority). Identify the chiral center and trace a curved or circular path from the highest to the lowest priority group. If the direction is clockwise, assign it \(R\). If the direction is anticlockwise, assign it \(S\). Do this for each isomer.

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