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The specific rotation, [alpha], is expre...

The specific rotation, `[alpha]`, is expressed as

A

`(alpha_(obs))/(l.c)`

B

`alpha_(obs)lc`

C

`(l.c)/(alpha_(obs))`

D

`(alpha_(obs))/(l.c^(2))`

Text Solution

Verified by Experts

The correct Answer is:
A
Specific rotation
`= ("observed rotation"("degress"))/("length"(dm)xx"concentration or density" (g//mL^(-1)))`
The value of the optical activity (or rotatory power is expressed as specific. The specific rotation, `[alpha]_(D)`, denfined to make it independent of length and concentration (or density) is a true physical constant:
`[alpha]_(D) = (alpha_(obs))/(l.c)`
Where `alpha_(obs)` is the obserbed rotation, in degrees, in a sample cell whose path length `(l)` is in decimeters `(dm)` and the concetration `(c )` is in `gmL^(-1)`. For pure liquid compounds the density `(d)` in `gmL^(1)` is used. The subscript `D` tells us that the wavelength of light used is the `D` line of the sodium spectrum. The temperature is indicated by a superscirpt and is usually `25^(@)C`, thus `[alpha]_(D)^(25^(@))`
Note that the sign and/or value of the specific rotation of a molecule cen't be deduced form its configuration.
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