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Chapter 13: Q2P (page 656)

Predict the chemical shifts of the protons in the following compounds

Short Answer

Expert verified

Alkene hydrogens give nearly 5.5 ppm NMR chemical shift. And the sp3hybridised carbon hydrogen give 0.8 ppm in NMR spectra.







Step by step solution

01

Alkene and sp3hydrogens

Alkene hydrogens give nearly 5.5 ppm NMR chemical shift. And the sp3hybridised carbon hydrogen give 0.8 ppm in NMR spectra.

02

 Phenyl and methyl hydrogens

Phenyl hydrogens give 7 ppm NMR chemical shift. And the methyl hybridised carbon hydrogen give 2.5 ppm in NMR spectra.

03

 Phenyl and methoxy hydrogens

Phenyl hydrogens give 7 ppm NMR chemical shift. And the methoxy hydrogen give 3.8 ppm in NMR spectra.

04

Alkene and Alkyne hydrogens

Alkene hydrogens give 5.5 ppm NMR chemical shift. And the alkyne carbon hydrogen give 2 ppm in NMR spectra.

05

Phenyl, carboxylic acid and methyl hydrogens

Phenyl hydrogens give 7 ppm NMR chemical shift. And the carboxylic acid carbon hydrogen give 13 ppm in NMR spectra and methyl is 2.5 ppm.

06

Methyl hydrogens

Methyl hydrogens give 1.8 ppm NMR chemical shift. But in presence of bromine the value is deshielded and increases near to 3.7 ppm in NMR spectra.

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Most popular questions from this chapter

Each of these four structures has molecular formula . Match the structure with its characteristic proton NMR signals. (Not all of the signals are listed in each case.)

(a) Sharpsinglet atδ8.0 andtriplet atδ4.0

(b) Sharpsinglet atδ2.0 andquartet atδ4.1

(c) Sharpsinglet atδ3.7 andquartet atδ2.3

(d) Broadsinglet atδ11.5 andtriplet atδ2.3

Question: How many signals would you expect to see in the 13CNMR of the following compounds? In each case, show which carbon atoms are equivalent in the 13CNMR.

For each compound shown below,

  1. Sketch theC13NMR spectrum (totally decoupled, with a singlet for each type of carbon), showing approximate chemical shifts.
  2. Show the multiplicity expected for each signal in the off-resonance-decoupled spectrum.
  3. Sketch the spectra expected using the DEPT-90 and DEPT-135 techniques.

Different types of protons and carbons in alkanes tend to absorb at similar chemical shifts, making structure determination difficult. Explain how the among the following four isomer 13C NMR spectrum, including the DEPT technique, would allow you to distinguish.

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.
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