MUTAROTATION

When aldehyde is first dissolved in water and the solution is put in optical part so that the surface polarized light passed. The first optical rotation show by sugar slowly change it way until it form a fixed constant rotation, this enrich the characteristic of the sugar. The phenomenon of change of rotation is term mutarotation. For proper clarity see fig 1.5. in the fig it will be observed that the glucose happen to change it form, which it yield α-D-glucose and β-D-glucose, in the cause of these change, the optical rotation convert α-glucose to an equilibrium mixture of α-β-form. The word ‘Carbohydrates’ define as a group of organic compounds, starting from Simple sugars monosaccharide to complex sugars polysacchacharides,

The mechanism behind this involved the opening of hemiacetal rings, when this ring is open it form a trace aldehyde form, and recondensation occur which form cyclic compound. But the aldehyde is extremely unstable and exists only as a transient.

A man called Tarent provides a clear proof, on his experiment he prepared two isometric form of D-glucose, in these experiments he used a crystallization method under different condition where he come to the conclusion bellow;

• As the D-glucose is crystallized from water or diluted in alcohol at a room temperature α-D-glucose separate poses first exact rotation of +112̊, in the process this change to constant rotation of +52.5̊.
• As crystallization begin from water at a temperature above 98̊C it form a different compound of β-form of the glucose separately this also have first exact rotation +19̊ it also change to constant rotation of +52.5̊

 

TARENT EXPERIMEMT

α-D-glucose 112̊                +52. 5̊                  +19̊ β-D-glucose this exist as isomeric form, in a solution it observed that it change to equilibrium mixture not considering the compound dissolved in the solution.

Glucose solution have approximately 2/3 of sugar and this sugar exist only as β-from and 1/3 sugar which exist in the equilibrium as α-form and this lie at constant equilibrium.

 

 

 

 

The illustrate form of pyranose and furanose form when glucose is dissolved in solution.

1. Pyranose: as it was suggested by a man called Haworth in 1929, he said in pyranose there are six rings that form the sugar, these sugar are called pyranose because pyran have the same rings of the oxygen and carbon.
2. Furanose: these sugar have five number rings, the reason of these compound been called furanose is because furan contain the same rings as sugar pyranose contain inside the hemiacetal formed. This take place due to the megine of the aldehyde or ketone groups with the alcoholic group –OH on the carbon via aldehyde or ketone group. In another form, sugar of pyranose is also formed by reaction of aldehyde or ketone group with the compound in questions. As suggested by Haworth projection and shown bellow