An unknown sugar is known to equilibrate between two forms, I and II, in aqueous solution. This equilibration can be followed by measuring the optical rotation of aqueous solutions of isolated samples of form I and II. When species I was dissolved in pure water and the optical rotation was measured, it gave a specific rotation of [?] = +42.0°. Over time, this value decreased to a constant value of [?] = +0.2°. • When species II was dissolved in pure water and the optical rotation was measured, it gave a specific rotation of [?] = -54.0°. Over time, this value decreased to constant value of [?] = +0.2°. • In each case, both forms I and II were shown to be present in the mixture at the end of the experiment.
An unknown sugar is known to equilibrate between two forms, I and II, in aqueous solution. This
equilibration can be followed by measuring the optical rotation of aqueous solutions of isolated
samples of form I and II.
When species I was dissolved in pure water and the optical rotation was measured, it gave a
specific rotation of [?] = +42.0°. Over time, this value decreased to a constant value of [?]
= +0.2°.
• When species II was dissolved in pure water and the optical rotation was measured, it gave a
specific rotation of [?] = -54.0°. Over time, this value decreased to constant value of [?]
= +0.2°.
• In each case, both forms I and II were shown to be present in the mixture at the end of the
experiment.
Calculate the ratio of the two forms I and II present at equilibrium and comment on any
assumptions made in making that calculation.
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