Posted by Hannah on Sunday, October 28, 2012 at 3:02pm.
I know that to calculate the specific rotation for a compound you do
observed rotation / path length(dm) * conc. (g/ml).
I am confused about how to calculate the specific optical rotation for a compound.
Thank you for your help!
Chemistry(Please help) - DrBob222, Sunday, October 28, 2012 at 3:12pm
I'm not understanding. You know the formula; substitute the numbers and solve for alpha.
Chemistry(Please help) - Hannah, Sunday, October 28, 2012 at 3:17pm
Oh ok, the question asks me to find the specific rotation for D-erythrose 4-phosphate which I determined was 50 and then it asks me to find the specific optical rotation for L-erythrose 4-phosphate so I thought that it would be a different formula.
Chemistry(Please help) - Hannah, Sunday, October 28, 2012 at 3:20pm
The path of length was given in cm so I converted it to dm but I am not sure if I calculated the concentration correctly. A 50 gram sample was dissolved in 10 mL solution so would I do 50/10?
Chemistry(Please help) - DrBob222, Sunday, October 28, 2012 at 3:49pm
Yes, path length is in dm and cncn is g/mL. In your case that is 50g/10 mL = 5 g/mL.
Chemistry(Please help) - Hannah, Sunday, October 28, 2012 at 4:22pm
ok thank you and for the specific rotation of L-erythrose 4-phosphate would it be the same as for D-erythrose 4-phosphate which I determined was 50 or would it be -50?
Chemistry(Please help) - DrBob222, Sunday, October 28, 2012 at 5:01pm
If one is + the optical isomer will be - but don't confuse D and L with d and l.
d is for dextro-rotatory(right handed) and l is for levo-rotatory(left handed) and they don't have anything to do with D- and L-.
Here is a LONG article where you can read more.
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