Answer to Question #86432 in Organic Chemistry for Gayatri

Question

a) Explain mutarotation in glucose by drawing suitable structures.
b) Define the following for oils and fats: i) Acid value ii) Saponification value iii) Iodine value.

Answer 1

a) Alpha and beta configurations of glucose can change spontaneously through intermediate open chain formation (the process of Mutarotation). Specific rotation of alpha form is +112⁰, specific rotation of beta form is +19⁰. There is gardual change in optical rotation of the solution. The initial optical rotation changes to a constant optical rotation (+52.5⁰). The constant specific rotation is due to resultant net optical activity of both alpha and beta anomers.

b) i) Acid value

The acid value (AV) is defined as the weight of KOH in mg needed to neutralize the organic acids present in 1g of fat and it is a measure of the free fatty acids (FFA) present in the fat or oil.

ii) Saponification value

Saponification value number is the number of milligrams of potassium hydroxide required to saponify 1g of fat. It is a measure of the average molecular weight (or chain length) of all the fatty acids present.

iii) Iodine value

The iodine value is the mass of iodine in grams that is consumed by 100 grams of fat. Iodine numbers are often used to determine the amount of unsaturation in fatty acids. This unsaturation is in the form of double bonds, which react with iodine compounds. The higher the iodine number, the more C=C bonds are present in the fat.