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?

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).

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

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That should ofcourse have been "vinyl carbons" not "vinyl protons"