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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

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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.

Step by step solution

01

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.

02

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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Most popular questions from this chapter

The following spectra are taken from a compound that is an important starting material for organic synthesis. Determine the structure, first by considering each spectrum individually, and then by considering all the spectra together. Assign peaks to show that your proposed structure accounts for all the major features of each spectrum. DEPT information is given in blue on the carbon NMR

The following proton NMR spectrum is of a compound of molecular formula C3H80.

  1. Propose a structure for this compound.
  2. Assign peaks to show which protons give rise to which signals in the spectrum.

Determine the ratios of the peak areas in the following spectra. Then use this information, together with the chemical shifts, to pair up the compounds with their spectra. Assign the peaks in each spectrum to the protons they represent in the molecular structure.

Possible structures:

A compound was isolated as a minor constituent in an extract from garden cress. Its spectra are shown here.

  1. Look at each spectrum individually and list the structural characteristics you can determine from that spectrum.
  2. Look at the set of spectra as a group and propose a tentative structure.
  3. Verify that your proposed structure accounts for the major features of each spectrum.

A new chemist moved into an industrial lab where work was being done on oxygenated gasoline additives. Among the additives that had been tested, she found an old bottle containing a clear, pleasant-smelling liquid that was missing its label. She took the quick NMR spectrum shown and was able to determine the identity of the compound without any additional information. Propose a structure and assign the peaks. (Hint: This is a very pure sample.)

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