There is a NMR problem that I\'ve been struggling with and I was wondering if th

Question

There is a NMR problem that I've been struggling with and I was wondering if there is anybody who can help me with it: a. Assign which atoms in the molecule give which chemical shifts in the H and C NMR in the alpha-terpinene=N-phenylmaleimide adduct, the spectra are provided in your lab manual. (The singlet at 7.26ppm in the H NMR and the triplet at 77.00ppm in the C Nmr are due to solvent.) Note: in some cases, it's not possible to determine the exact assignment, if two or more H or C are nearly chemically equivalent and cannot be distinguished mention this on the blank provided.

H NMR (CDCL3) e.g H1 0.50ppm (3H, s) the CH3 on the ring

H3 ___ppm (__H, __) ______________

H4 ___ppm (__H, __) ______________

H6 ___ppm (__H, __) ______________

H7 ___ppm (__H, __) ______________

H8 ___ppm (__H, __) ______________

H9 ___ppm (__H, __) ______________

H10 ___ppm (__H, __) ______________

H11 ___ppm (__H, __) ______________

H12 ___ppm (__H, __) ______________

H16 ___ppm (__H, __) ______________

H17 ___ppm (__H, __) ______________

H18 ___ppm (__H, __) ______________

C NMR (CDCl3)

C1 ___ppm, _____________

C2 ___ppm, _____________

C3 ___ppm, _____________

C4 ___ppm, _____________

C5 ___ppm, _____________

C6 ___ppm, _____________

C7 ___ppm, _____________

C8 ___ppm, _____________

C9 ___ppm, _____________

C10 ___ppm, _____________

C11 ___ppm, _____________

C12 ___ppm, _____________

C13 ___ppm, _____________

C14 ___ppm, _____________

C15 ___ppm, _____________

C16 ___ppm, _____________

C17 ___ppm, _____________

C18 ___ppm, _____________

b. Why do the two isopropyl methyl groups have different chemical shifts?

c. Is there any evidence for exo- vs. endo- in the NMR? Explain why/why not.

Explanation / Answer

A. As the your NMR picture is not clear here,so I have given the approx ( very much close to your NMR) Data below. Please do cross check once.

H3 6.05ppm (1H, d) vicinal hydrogen attached with the ring.

H4 6.1ppm (1H, d) vicinal hydrogen attached with the ring.

H6 1.5-1.6ppm (2H, t) bridged -CH2 group

H7 1.5-1.6ppm (2H, t) bridged -CH2 group.

H8 1.3-1.4ppm (1H, septet) -CH proton of isopropyl group.

H9 1.0ppm (3H, d) methyl of isopropyl group.

H10 1.1ppm (3H, d) methyl of isopropyl group

H11 2.70ppm (2H, t) CH proton of fused carbon between two ring

H12 2.75ppm (2H, t) CH proton of fused carbon between two rings.

H16 7.5ppm (1H, d) aromatic hydrogen

H17 7.4ppm (1H, t) aromatic hydrogen

H18 7.2ppm (1H, t) aromatic hydrogen

C NMR (CDCl3)

C1 18ppm,methyl carbon

C2 33ppm, bridge head carbon

C3 138-140ppm, double bonded carbon (exocyclic)

C4 138-140ppm, exocyclic double bonded carbon

C5 50-52ppm, bridge head carbon

C6 21-22ppm, fused carbon

C7 44-45ppm, fused carbon

C8 30-31ppm, -CH group of isopropyl group

C9 20-22ppm, methyl carbon of isopropyl group

C10 20-22ppm, methyl carbon of isopropyl group

C11 50-52ppm, fused carbon between two rings

C12 56-58ppm, fused carbon between two rings

C13 175-177ppm, carbonyl carbon

C14 176ppm, carbonyl carbon

C15 133-134ppm, aromatic carbon

C16 130-131ppm, aromatic carbon

C17 130-132ppm, aromatic carbon

C18 130-132 ppm, aromatic carbon

B. The chemical environment of these two isopropyl methyl group is same.it should show same chemical shift. But due to symmetry reason it will show chemical shift at different region.

C. Exo cyclic and endocyclic double bond can easily be identified by NMR. Exocyclic double bond with show geminal coupling value (J)=2 Hz whether endo cyclic double bond will show vicinal(cis hydrogen) coupling constants value at around 7-8 Hz.

If you like my answer,please do rate my question.

Thanking you.

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