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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

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?

If the imaginary replacement of either of two protons forms enantiomers, then those protons are said to be enantiotopic.The NMR is not a chiral probe, and it cannot distinguish between enantiotopic protons. They are seen to be 鈥渆quivalent by NMR鈥�.

  1. Use the imaginary replacement technique to show that the two allylic protons (those on) of allyl bromide are enantiotopic.
  2. Similarly, show that the two HCprotons in cyclobutanol are enantiotopic.
  3. What other protons in cyclobutanol are enantiotopic?

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.

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

  1. Acid catalysis
  2. Base catalysis.

The three isomers of dichlorobenzene are commonly named ortho-chlorobenzene, meta-chlorobenzene, and para-chlorobenzene. These three isomers are difficult to distinguish using proton NMR, but they are instantly identifiable usingNMR.

  1. Describe how carbon NMR distinguishes these three isomers.
  2. Explain why they are difficult to distinguish using proton NMR.
See all solutions

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