chemistry gurus, need help.

apple

in our lab, we made ethanol through the fermentation of sucrose.
one of the questions is explain how an H NMR spectrum of your distillate could be used to find the percentage of alcohol.
any help?  

  take the integral peak values of your ethanol and compare them with a standard value (should know this from a reaction equation) because the signals are proportional to the number of protons that they represent (which can help you determine moles).

Originally Posted by jun14scr
in our lab, we made ethanol through the fermentation of sucrose.
one of the questions is explain how an H NMR spectrum of your distillate could be used to find the percentage of alcohol.
any help?

  

  alright. good stuff. i was thinking something along those lines but wanted to make sure. thanks!
by standard value, you mean an H NMR of a 100% ethanol solution?  

  quite possibly ... i was thinking more of this ... what you want is an inert standard (example would be cyclododecane because it gives you one isolated peak) in the reaction mixture with a recorded ratio of that standard to whatever you're reacting.  
in the NMR signals, you compare the number of moles of your product to the standard.  if you use cyclododecane, it has 24 protons so an equation would be
np = nc x Ap/Ac x 24/p
np = moles product
nc = moles of cyclododecane
Ap = area of a particular proton in product
Ac = area of cyclododecane protons
p   = particular proton in product
you can use the mole amount to get your percentage

Originally Posted by jun14scr
alright. good stuff. i was thinking something along those lines but wanted to make sure. thanks!
by standard value, you mean an H NMR of a 100% ethanol solution?

  

  grief. if i put that on there she'd know someone helped me. i'm only in orgo II right now. thanks for your help.