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Chapter 13: 13-53P (page 707)

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

Short Answer

Expert verified

The given structures are matched with their characteristic proton NMR signals in each case.

Protons are shown in bold which gives NMR signals

Step by step solution

01

Step-1. Explanation of part (a):

The description of chemical shift and signals of part (a) matches with structure 4. In structure 4, there exists a sharp singlet of 1 hydrogen atom which is attached to the carbonyl carbon and its chemical shift value is 8.0. The two hydrogen atoms exhibit triplet pattern due to adjacent methylene hydrogen atoms and their chemical shift value is 4.0 due to attachment with oxygen which is electronegative.

Structure matched with given description

02

Step-2. Explanation of part (b):

The description of chemical shift and signals of part (b) matches with structure 3. In structure 3, there exists a sharp three hydrogen singlet of methyl group at chemical shift 2.0 and quartet for two hydrogens at chemical shift 4.1 due to presence of adjacent three hydrogens of methyl which splits the signal for these two hydrogen atoms into quartet.

Structure matched with given description

03

Step-3. Explanation of part (c):

The description of chemical shift and signals of part (c) matches with structure 2. In structure 2, there exists a sharp three hydrogen singlet at chemical shift 3.7 of methoxy group hydrogens. Hydrogen atoms of methylene group which are adjacent to carbonyl group shows quartet splitting pattern due to presence of three hydrogens of methyl group adjacent to it and have chemical shift value 2.3.

Structure matched with given description

04

Step-4. Explanation of part (d):

The description of chemical shift and signals of part (d) matches with structure 1. In structure 1, there exists a broad singlet of hydrogen of a hydroxyl group. The signal is broad due to acidic hydrogen of hydroxyl group which is exchangeable. The chemical shift value of this hydrogen is high due to direct attachment with electronegative atom like oxygen. The hydrogens of methylene group which are adjacent to carboxylic group shows a triplet pattern due to two hydrogens adjacent to it and shows chemical shift 2.3.

Structure matched with given description

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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.

A laboratory student was converting cyclohexanol to cyclohexyl bromide by using one equivalent of sodium bromide in a large excess of concentrated sulfuric acid. The major product she recovered was not cyclohexyl bromide, but a compound of formula C6H10that gave the following 13CNMR spectrum:

  1. Propose a structure for this product.
  2. Assign the peaks in the 13CNMR spectrum to the carbon atoms in the structure.
  3. Suggest modifications in the reaction to obtain a better yield of cyclohexyl bromide.

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?

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.

Draw a splitting tree, similar to Figures 13-32 and 13-33, for proton Hc in styrene. What is the chemical shift of proton Hc?
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