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Manipal Medical Manipal Medical Solved Paper-2015

  • question_answer
    The specific rotation of \[\alpha \]- and \[\beta \]-forms of a monosaccharide are +29° and -17° respectively. When either form is dissolved in water the specific rotation of the equilibrium mixture was found to be +14°. What is the composition of these forms?                 \[\alpha \]- form \[\beta \]- form                 \[\alpha \]- form \[\beta \]- form

    A) 67.4%      32.6%    

    B) 60%         40%

    C) 70%                 30%                 

    D) 50%          50%

    Correct Answer: A

    Solution :

    Suppose that the fraction of \[\beta \]-from = x Then, fraction of \[\alpha \]-from = 1 ? x \[x\times (-17)+(1-x)29=14\] Or,                     \[-17x+29-29x=14\] Or,                                 \[-46x+29=14\] Or,                                                \[15=46x\] Or, \[x=\frac{15}{46}=0.326=32.6%=\beta \]- form \[1-0.326=0.674=67.4%=\alpha \]- form


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