ijsup Posted February 19, 2009 Share Posted February 19, 2009 Hi. I just did a lab where we dehydrated 2-methylcyclohexanol. We were told it would form 1-methylcyclohexene and/or 3-methylcyclohexene and we are asked to determine the major product. I figure the major product is 1-methylcyclohexene because it is the most substituted c=c. However, we are supposed to determine it using C13 NMR. We are given the "hint" to figure out how the spectra of the 1-and 3- methylcyclohexenes would differ. I don't know how to figure this out. Any suggestions? Link to comment Share on other sites More sharing options...
UC Posted February 19, 2009 Share Posted February 19, 2009 is there going to be a difference in the chemical shifts for the more substituted alkene versus the almost-symmetrical one? This database has everything you could possibly ever need as far as numbers. Both compounds and the chemical shifts are given under cyclohexene: http://www.chem.wisc.edu/areas/reich/Handouts/nmr-c13/cdata.htm Of course, the point of using C13 NMR is out the window if you can't understand why the shifts differ between the two (and I suspect that you will be required to explain). Link to comment Share on other sites More sharing options...
Tartaglia Posted February 21, 2009 Share Posted February 21, 2009 Its actually even simpler than that. Since 99% of C-13 nmr are proton decoupled, the vinyl protons in 3-methylhexene will both exhibit Nuclear Overhauser enhancement, but only one will in the 1-methylcyclohexene Merged post follows: Consecutive posts mergedThat should ofcourse have been "vinyl carbons" not "vinyl protons" Link to comment Share on other sites More sharing options...
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