Increasing cell length increases specific rotation?

[pineappletree]

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pertaining to measuring the rotation of polarized light from stereoisomers, i was wondering how the rotation increases as the cell length increases...

This doesn't really seem to make sense as the equation for observed specific rotation has cell length on the denominator

 

[loveoforganic]

Where are you getting that? Should definitely decrease according to the equation.

 

[pineappletree]

It is BR orgo chapter 3, question #16


Which of the following explanations does NOT account for an observed optical rotation greater than that of a positive literature value for a pure species?

A.) Both enantiomers are present in an unequal amount
B.) The solution is too concentrated
C.) The cell for the polarimeter is too long
D.) the wavelength of light being used is greater than that of the standard sodium light used

The answer is A, but wondering why C is wrong...

 

[kentavr]

The specific rotation is measured as
Ad=A/(L*[x]) (and published in the literature)
Then, to find the observed angle(in experiment) we have
A=Ad*(L*[x])
That means, the longer the length the larger the angle (up until 360)
And that can explain larger angle observed. Choice C.
But the question asked, what does not explained it. So C is not the answer.
From common sence, the longer the tube,
the more interaction of light with chirality center we get, angle should be larger.