HB: Aromatic hydrogens usually exhibit peaks around 7-8ppm, A coupling constant of 8Hz and splitting pattern of a doublet shows that this couples with HA. HC: Through the inductive effect, the two chlorines significantly deshield this hydrogen. HD: The two neighboring oxygens serve to strongly deshield this hydrogen. Also, this hydrogen has no two- or three-bond neighbors to couple with. HE:The inductive effect of the bromine results in the downfield shift of this hydrogen. Furthermore, this hydrogen exhibits the expected splitting pattern (dd) with coupling constants seen correspondingly in HR and HM. HF: This shift is expected for a hydrogen attached to the same carbon as an oxygen and shows the expected doublet of doublet splitting pattern. HG, HH: These two hydrogens are deshielded by the adjacent electronegative oxygen atom, giving them shifts around 4 ppm, which is expected for hydrogens on a carbon atom bonded to an oxygen. The hydrogens are not chemically equivalent because of the chiral centers in the molecule. HI: This shift is expected for a hydrogen attached to the same carbon as an oxygen and shows the expected ddd splitting pattern with corresponding coupling constants that paired with HF, HT, and HT’. HJ: The closeness of HJ to the two chlorines deshields this hydrogen. The appropriate splitting pattern and coupling constants with HC and HF further prove this assignment. HK: The closeness of HK to the aromatic ring aids in deshielding this hydrogen. Moreover, the coupling constants seen in HK match up with those observed in HR, HM, and HP. HL: This hydrogen is shifted downfield as it is near an electronegative oxygen atom. HM: The inductive effect of the neighboring bromine serves to slightly desheild this hydrogen. As it is diastereotopic with HR, it is expected to exhibit a ddd splitting pattern. HN: Hydrogens of the methyl of toluene-like benzene derivatives are expected to show peaks around 2.5ppm. Moreover, the lack of two- or three-bond neighbors results in this peak appearing as a singlet. HO: The polarity of the carbonyl bond causes the deshielding of HO and its five three-bond neighbors result in the observed multiplet. HP: Again, the polarity of the carbonyl bond causes the deshielding of HP. Furthermore, the coupling constant observed in HP matches with its partner, HK. HQ, HS: These two hydrogens are diastereotopic, and show shifts slightly downfield of what is expected of a methyl group bonded to a carbon atom. This can be explained through the inductive effect due to the nearby oxygen atom. HR: The inductive effect of the neighboring bromine serves to slightly desheild this hydrogen. As it is diastereotopic with HM, it is expected to exhibit a ddd splitting pattern. HT: The neighboring oxygen most likely serves to deshield this hydrogen slightly. Additionally, its diastereotopic relationship with HT’, results in a ddd splitting pattern. HT': This hydrogen was not assigned a shift in the 1HNMR data provided, however, due to the similar chemical environment of HT, we can expect HT’ to display the same shift and splitting pattern. HU: The hydrogens of this methyl group have no two- or three-bond neighbors and are thus expected to display a singlet splitting pattern. The neighboring electronegative atoms deshield these hydrogens slightly. HV: The hydrogens of this methyl group have a single three-bond neighbor and therefore shows a doublet splitting pattern. The nearby ester results in the downfield shift of these hydrogens. HW: The increase in electron density on the central carbon of the tert-butyl group (from the electronegativity difference between silicon and carbon) results in the shielding effect on these hydrogens. As these hydrogens have no three-bond neighbors, they display singlets. HX, HY: The significant electronegativity difference between silicon and carbon results in an increase of electron density on the carbons of HX and HY. The hydrogens of carbon Y are slightly more downfield shifted as they are geometrically closer to two oxygens. HZ: Though no chemical shift was assigned to this hydrogen, the hydrogen of hydroxyls are expected to exhibit peaks around 4-1.57ppm. |
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