Dear Friends,
I have the following question for those of you who are familiar with DOSY or
diffusion in general:
For a reaction between two molecules A and B, where A is a bulk molecule
with a molecular weight of about 2000 while B is an 8-carbon diamine
(H2N-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-NH2) and presumably the middle part
(carbons 3-6) of B will interact with A, we were expecting from DOSY one
diffusion coefficient if they form AB, assuming a molar ratio A:B=1:1 and
the reaction completes, and two separate coefficients if they did not react
at all (arguably there could be more coefficients if equilibrium).
Surprisingly, the 1H DOSY showed that A plus the protons on the middle 4
carbons of B occurred at roughly the diffusion coefficient of A while the
protons on the 4 end carbons of B appeared at the diffusion coefficient of
B. Since B did not break into pieces during the reaction, how could it occur
at two different diffusion rates? We are puzzled by the results. I'll
appreciate if you could shed light on this observation.
Cheers,
Jerry
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Jerry Hu, Ph.D. Email:
jghu_at_mrl.ucsb.edu
Project Scientist Tel:
(805)893-7914
Materials Research Lab, UCSB Fax: (805)893-7914
Santa Barbara, CA 93106
Received on Wed May 18 2011 - 07:41:56 MST