6. (20) The compound (S) 3-chloro-1,2,propanediol is shown below. A sophomore ch

Question

6. (20) The compound (S) 3-chloro-1,2,propanediol is shown below. A sophomore chemistry major looked at this structure and predicted a 1H NMR spectrum to show 2 doublets and a quintet (3 signals, nine lines total). The 1H NMR spectrum (400 MHz), however shows upwards of 24 lines as seen in Appendix D. In the spectrum, the OH protons are not shown and there is no coupling to the OH proton HC OH HO Cl Ha Hb Hd He 3-chloro-1,2-propanediol a) Thoroughly explain to a sophomore chemistry major why the spectrum is so complex and give a line list for each of the labeled protons a, b, d, and hemical shifts should e. be expressed to 0.01 ppm and coupling constants to 0.1 Hz. (Hc is the signal 63.92) b) Based on your assignments for a, b, d, and e, what should Ho (the downfield signal) appear as? Does it?

Explanation / Answer

(a) The given spectrum is complex due to chirality

All the protons show separately in the 1H NMr spectrum

Assignment,

Ha : doublet of doublet at 3.56 ppm

Hb : doublet of doublet at 3.60 ppm

Hd : doublet of doublet at 3.64 ppm

He : doublet of doublet at 3.74 ppm

Hc : multiplet at 3.91 ppm

(b) Hc would be the most downfield signal in the NMR and would appear at,

3.91 ppm as multiplet as it is the chiral center.

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