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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: SantiagoJordan on February 07, 2020, 01:36:45 PM

Title: How does polarimeter assign + or - sign to the value of optical rotation?
Post by: SantiagoJordan on February 07, 2020, 01:36:45 PM

We got into bit discussion in a lab about how exactly polarimeteres work. The problem we encountered is that how exactly does polarimeter distinguish between lets say +350° or -10°? I was thinking that the detector measures up to +180° and whatever is higher gets reverted into the -part. ie. +190° is shown as -170° but this was disproved by a collegue who told that there are compounds with specific rotation above 360°

thx

Title: Re: How does polarimeter assign + or - sign to the value of optical rotation?
Post by: Borek on February 07, 2020, 04:20:49 PM

Polarimeter doesn't, but you can always dilute the sample and see what the new angle is. Can you predict what kind of change you would measure for half dilution and 10° vs 370° specific rotations?

Title: Re: How does polarimeter assign + or - sign to the value of optical rotation?
Post by: sjb on February 08, 2020, 02:51:42 AM

Also, compare the discussion at https://www.reddit.com/r/chemistry/comments/f07t4k/how_does_polarimeter_assign_or_sign_to_the_value/