Question

Calculate the specific rotation of invert sugar given that $[\alpha {]}_D=+{52.7}^o$ for D-glucose and $[\alpha {]}_D=-{92.4}^o$ for D-fructose.

• A. $+{19.9}^o$
• B. $-{19.9}^o$
• C. $+{25.0}^o$
• D. $-{25.0}^o$

Answer 1

The correct option is B $-{19.9}^o$

Invert sugar is an equimolar mixture of D-glucose and D-fructose. It is obtained by the hydrolysis of sucrose. The specific rotation is one-half the sum of the of individual monosaccharides: $\frac{1}{2}[+{52.7}^o+(-{92.4}^o\left)\right]=-{19.9}^o]$