Chapter 13: Q.13-42P (page 703)
The following off-resonance-decoupled carbon NMR was obtained from a compound of formula. Propose a structure for this compound and show which carbon atoms give rise to which peaks in the spectrum.
Short Answer
Step by step solution
Off-resonance-decoupled carbon NMR:
In an off resonance-decoupled carbon NMR spectrum, the coupling between each carbon atom and each hydrogen attached directly to it is observed. The n+1 rule can be used to determine whether a given carbon atom has three, two or no hydrogens attached. The off-resonance decoupled spectrum retains the couplings between carbon atom and directly attached protons but effectively removes the couplings between the carbon and more remote protons.
Determination of structure from given spectrum:
From the given off resonance-decoupled carbon NMR spectrum, the multiplicity of the peaks in this off resonance-decoupled spectrum shows two differentand a
. There is only one way to assemble these pieces with three chlorine atoms as the molecular formula is
.
The chemical shift values and splitting pattern have been assigned to the peaks in the spectrum, higher chemical shift value of 75 indicates that carbon is attached to more electronegative atoms as more electronegative atoms create the deshielded environment means area of less electron density, thus increasing the value of chemical shift. The chemical shift value of 60 also indicates attachment of electronegative atom such as chlorine in this case, due to which value of chemical shift increases. The multiplet at 0 is TMS. Thus, the proposed structure will be of 1,1,2-trichloropropane.
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