[nj_bartel]

I'm having trouble figuring out how to do this :/  Just a point in the right direction would be very appreciated.  I already determined that there was at least some exo product present due to ~3.61 Hz J3 coupling at the peak at 3.63 ppm, by the Karplus relationship.

Spectrum attached.

Edit:  Spectrum is attached as a PDF.  Can attach MestReNova file if additional clarity is needed. (scratch that, nova files can't be uploaded.  Can post individual zooms then, if necessary)

Thanks

Edit:  Upon analyzing my TLC plate, I get 2 spots, Rf 0.42 and Rf 0.60.

Lit Values - Starting material: 0.68,  Endo: 0.47,  Exo: 0.33

Sigh.  This isn't going well 

[azmanam]

what's the reaction?

[nj_bartel]

N-phenylmaleimide and furan

[azmanam]

Go get a NOESY.  If you've got more than 20 mgs or so, you should get a nice one in 20 min on a 400 magnet.  Endo product will show enhancement between phenyl group and alkenes.  Exo product may show enhancement between methine protons (from original double bond of maleimide) and alkene (3.1 angstroms may be pushing it, but you have structural rigidity working for you).

Both will show enhancement between alkene and bridgehead.  And bridgehead and methine protons (actually looking again, you may not get a good enhancement b/t the bridgehead and methine protons in the exo product... further evidence).  Then find a region where the two diastereomers have good separation in the NMR and take the ratio of the endo:exo protons (remember the molecule is symmetrical and each signal is really 2 protons).

[nj_bartel]

Sorry!  I should have specified.  This is for O. Chem II lab, so the spectrum I've obtained is all I'm allowed to work with.  I was thinking the peak at 2.95 would be the endo proton version of the exo-proton I measured the coupling on, but it's a singlet, which doesn't make sense to me.

Edit:  Pulling lit values on the specific dihedral angles I'm working off of.  Picture attached.  38 for the endo, 80 for the exo.

[nj_bartel]

So, I would think I'd expect to see, assuming I have some endo product (which seems to be the case from TLC, even though the values weren't really right at lit), that I'd have a doublet of doublets with J3 ~6-8 Hz, with the peak somewhere slightly upfield or downfield of the doublet of doublets I'm assuming to be exo.  But all there is in that region is the singlet at just below 3 ppm.  Is that correct?

Are you thinking that the peak I thought was exo is actually endo?

[azmanam]

can you zoom in between 5.5 and 2.5 ppm (and if you can, what are the j values for the 4 peaks in that region)

I don't yet know which peaks are which isomer.

[nj_bartel]

More info coming.

I'm unsure of the coupling at 5.375 ppm.  It's a weird multiplet.  The coupling at 3.63 ppm is 3.62 Hz.  The other peak upfield is a singlet.

[azmanam]

I think you have enough information to assign your peaks.  I'd focus on the methines.  The dihedral angles and coupling constants will be key, imho.

What's your guess?

[nj_bartel]

Talked a bit with some people in my class and am leaning toward I got essentially all exo (no endo), along with some starting material.

Peak assignment -

1.45: water
2.95: protons on carbon alpha to carbonyl on exo product
3.63: bridgehead protons on exo product
5.37: vinylic protons on exo product
6.51: vinylic protons on SM
7.2: chloroform

Didn't really mess with the aromatics.

Sound good I hope?  Already turned the report in

[azmanam]

I guess it would also have been helpful to know when the nmr was taken.  After workup/before column? after column? one spot or mixture of two spots after column?

Based on two peaks integrating to 1, two peaks integrating to 0.82 and one peak integrating to 0.82, I see it as a 1.25:1 mixture of diastereomers.  1.25 endo, 0.82 exo. 

I put the protons integrating to 0.82 as the exo because a) it should be the minor product and b) the splitting at 3.5 is predicted from the 40 deg dihedral angle b/t methine and carbinol.  1 goes with endo because a) it should be major and b) dihedral angle of 80 gives j value close to zero - making any splitting appear as a singlet, which you see.

so i say
3 = endo methine
3.5 exo methine
5.3 endo carbinol
5.4 exo carbinol
6.5 both vinyls

if the integrations weren't so even across the board, I might be convinced of mix of pdt and sm.  as such, I guess mix of diastereomeric products.

let us know how it turns out.  (and tell your instructor this can all be cleared up with a 20 min NOESY )

[nj_bartel]

Sorry, I feel like I keep with holding information

The furan was pure, reagent grade.  The N-phenylmaleimide was synthesized by me and recrystallized.  The two were combined in a flask and stoppered, then kept at 0 oC for a week.  It was then heated under reflux for 5 hours.  The product was collected by filtration (no recrystallization).  It was this that was put through NMR and TLC.

I was originally thinking something along the lines of what you're saying, but there's no splitting on that peak at 2.95, which doesn't make sense to me.  The lit values I was given has the exo dihedral at 80 and the endo dihedral at 38.

[azmanam]

when is a singlet not a singlet?  When it should be a multiplet but the j value is so small that all the peaks coalesce.  The expected j value for an 80 degree dihedral angle, from the karplus curve, should be essentially nonexistant.  That's why I'm ok with it being a singlet.

Also, were the two reacted at a 1:1 stoichiometric ratio?  Is maleimide a solid?  Furan should wash through with your filtration, so I don't know how I feel about it hanging around for the NMR.

I can't say with certainty that the NMR is a mix of pdts, but I'll stand by my guess

[nj_bartel]

Gotcha, wasn't thinking about potential NMR resolution.

Furan was reacted in excess.  Maleimide is a solid.  During the filtration, only a small quantity of solid (all adhered to filter, unremovable) was filtered off.  In the filtration flask, the product precipitated.  On a new filter, that precipitate was then collected.

Thanks for your help