Chapter 16, Problem 20P

Interpretation Introduction

Interpretation:

The carbonyl group of each of the eight $\text{D-aldohexoses}$ is reduced with ${\text{NaBH}}_{\text{4}}$ and protonated with $\text{HCl}$. Among the reduced and protonated products, the one that is optically active has to be found.

Concept Introduction:

Reduction Reaction: The aldehyde and ketones in the presence of strong reducing reagent (like $NaB{H}_4,LiAl{H}_4,Na/N{H}_3$ etc.,) the carbonyl compound reduced saturated alkanes, alcohols. If the keto group involves in the reduction process of $NaB{H}_4$, this carbonyl group reducing to give the different type alcohols.

Example:

  

Acid Catalyzed Hydration Reaction: The reaction involves breaking of phi bonds between carbon-carbon multiple bonds and addition of alcohol to more substituted position of carbon in the molecule.

First step is the acid donates proton to the alkene which leads to the formation of more stable carbo cation.

Then, the water is added to the given alkene through acid catalyzed reaction where the water gets added to the carbo cation finally, the removal of one proton from oxonium ion (oxygen with one positive charge) using water results in the formation of product.

Optical activity: molecule or substances that can rotate the plane-polarized light are said to be optically active.

Meso compound are optically inactive, because meso compound is a stereoisomer with an identical or superimposable mirror image.

Plane of symmetry: When structure of the compound can be cut into two equal halves along the plane. Then such plane is called as plane of symmetry.

The stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in different in each isomer.