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Chapter 13: Q.33P (page 701)

Question: An unknown compound has the molecular formula C9H11Br. Its proton NMR spectrum shows the following absorptions: singlet, d7.1, integral 44 mm singlet, d2.3, integral 130 mm singlet, d2.2, integral 67 mm Propose a structure for this compound.

Short Answer

Expert verified

Answer

The unknown compound is 2 bromo-1,3,5,trimehylbenzene

Step by step solution

01

Introduction to NMR spectroscopy

Proton magnetic resonance (PMR) is a particular branch of NMR spectroscopy where the nucleus is a proton. NMR and PMR spectroscopies are principally considered to be the same.

02

Explanation

The proton NMR spectrum for the unknown compound has the molecular formula C9H11Br and can be drawn as shown below:

Hence, the compound with the molecular formula C9H11Br is 2 bromo-1,3,5,trimehylbenzene .

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Most popular questions from this chapter

Sets of spectra are given for two compounds. For each set,

(1) Look at each spectrum individually and list the structural characteristics you can determine from that spectrum.

(2) Look ar the set of spectraas a group and purpose a tentative structure.

(3) Verify that your proposed structure accounts for the major features of each spectrum. The solution for compound 1 is given after the problem but go as far as you can before looking at the solution.

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.

Propose mechanisms to show the interchange of protons between ethanol molecules under

  1. Acid catalysis
  2. Base catalysis.

Phenyl Grignard reagent adds to 2-methylpropanal to give the secondary alcohol shown. The proton NMR of 2-methylpropanal shows the two methyl groups as equivalent (one doublet at1.1), yet the product alcohol, a racemic mixture, shows two differentdoublets, one at0.75 and one around1.0.

  1. Draw a Newmann projection of the product along the C1-C2 axis.
  2. Explain why the two methyl groups have different NMR chemical shifts. What is the term applied to protons such as these?

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.
See all solutions

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