1H-NMR Spectral Correlation
Molecule (+)-29: 4.63 (d, J= 7.0 Hz, 1H), 4.32 –4.26 (m, 2H), 3.94 (dd, J= 10.3, 5.2 Hz, 1H), 3.87 (s, 1H), 3.68 (s, 1H), 3.29 (s, 3H), 2.39 (dt, J= 14.8, 3.5 Hz, 1H), 2.23 –2.14 (m, 1H), 2.14 –2.02 (m, 1H), 1.91 –1.82 (m, 2H), 1.74 –1.66 (m, 1H), 1.38 (s, 3H), 1.34 (s, 3H), 1.11 (d, J= 6.8 Hz, 3H), 0.94 (s, 9H), 0.15 (s, 3H), 0.00 (s, 3H)
Explanations:
0.00 (s, 3H) and 0.15 (s, 3H): I/J The base peak at 0 ppm for H-NMR is usually due to bonding between carbon and silicon atoms. This is a diastereotopic pair of methyl groups
.94 (s, 9H): K This is 9H group is attached to a silicon atom. Silicon is less electronegative than Carbon thus shielding this tert-butyl group more.
1.11 (d, J= 6.8 Hz, 3H): F This 3H group is quite shielded because the carbon to which it is bonded is surrounded by other sp3-hybridized carbon atoms. This group is split into a doublet because of the single hydrogen on the carbon bonded to this methyl group.
1.34 (s, 3H): A/B These two methyl groups each integrate to 3H- as expected- and experience no splitting because they have no nearby H neighbors. Since they are nearly identical, it makes sense for both groups to have nearly the same chemical shift. (A’s proximity to more oxygens could shift it slightly more downfield than B.)
1.38 (s, 3H): G This methyl group integrates to 3H- as expected- and experience no splitting because it lacks nearby H neighbors. This methyl is more shielded than C and less shielded than A, B, and R (which are the other 3H methyl groups in the molecule). As a result, G is found in between these other methyl groups.
1.74 –1.66 (m, 1H): S This 1H group is quite shielded, as it is surrounded by sp3 carbon atoms. it is split into a multiplet by hydrogen groups Q, R and T.
1.91 –1.82 (m, 2H): M/N This peak corresponds to the 2 hydrogen group on the ketone. This is normally would be considered a diastereotopic pair, but this integrates to 2H. Additionally, this is a typical shift for a ketone’s hydrogens.
2.14 –2.02 (m, 1H): O/P This peak corresponds to the other 2 hydrogen group in the cyclohexane ring. This is considered a diastereotopic pair since two separate peaks are found. These hydrogens split each other and also have nearby neighbors that create the multiplet.
2.39 (dt, J= 14.8, 3.5 Hz, 1H): Q This peak corresponds to the one hydrogen group which is split by three hydrogen groups.
3.29 (s, 3H): C This peak corresponds to the distal methoxy group. This shift of 3.29 is typical of an ether.
3.68 (s, 1H): R This peak corresponds to the hydrogen on the carbon proximal to the MOMO group, which acts as an electron withdrawing group, causing the peak to be downfield due to shielding.
3.87 (s, 1H): T This peak corresponds to the hydrogen on the carbon proximal to the oxygen and methyl groups. This hydrogen is deshielded, as it is a two-bond and three-bond neighbor to an electronegative oxygen atom and a methyl group. This hydrogen is split by two other three-bond 1H neighbors: groups S and U.
3.94 (dd, J= 10.3, 5.2 Hz, 1H): U This hydrogen is very deshielded, as it is a two-bond and three-bond neighbor to two electronegative oxygen atoms. This hydrogen is split by two other three-bond 1H neighbors: groups F and T.
4.32 –4.26 (m, 2H): D/E This peak is represented by the 2 hydrogens between the two oxygen atoms. Again, this is normally a diastereotopic pair, but because this integrates to 2H we said its D/E. Additionally, this group is heavily shifted downfield because it is proximal to two electronegative oxygen atoms.
4.63 (d, J= 7.0 Hz, 1H): L This peak is represented by the singular ketone hydrogen that is also proximal to the oxygen. This single hydrogen is next to two extremely electron withdrawing groups. Therefore, it is the most downfield hydrogen.