Posted by Hannah on .
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,
I'm not understanding. You know the formula; substitute the numbers and solve for alpha.

Chemistry(Please help) 
Hannah,
Oh ok, the question asks me to find the specific rotation for Derythrose 4phosphate which I determined was 50 and then it asks me to find the specific optical rotation for Lerythrose 4phosphate so I thought that it would be a different formula.

Chemistry(Please help) 
Hannah,
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,
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,
ok thank you and for the specific rotation of Lerythrose 4phosphate would it be the same as for Derythrose 4phosphate which I determined was 50 or would it be 50?

Chemistry(Please help) 
DrBob222,
If one is + the optical isomer will be  but don't confuse D and L with d and l.
d is for dextrorotatory(right handed) and l is for levorotatory(left handed) and they don't have anything to do with D and L.
Here is a LONG article where you can read more.
http://en.wikipedia.org/wiki/Chirality_%28chemistry%29