In a 300-MHz spectrometer, the protons in iodomethane absorb at a position 650 Hz downfield from TMS.

(a) What is the chemical shift of these protons?

(b) What is the chemical shift of the iodomethane protons in a 60-MHz spectrometer?

(c) How many hertz downfield from TMS would they absorb at 60 MHz?

Predict the chemical shifts of the protons in the following compounds.

(a)

(b)

Determine the number of different kinds of protons in each compound.

(a) 1-chloropropane

(b) 2-chloropropane

(c) 2,2-dimethylbutane

The NMR spectrum of toluene (methylbenzene) was shown in Figure 13-11.

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(a) How many different kinds of protons are there in toluene?

(b) Explain why the aromatic region around d7.2 is broad, with more than one sharp absorption.

Draw the NMR spectra you expect for the following compounds.

(a)

Draw the NMR spectra you expect for the following compounds.

(b)

An unknown compound (C₃H₂NCl) shows moderately strong IR absorptions around 1650 cm^–1 and 2200 cm^–1. Its NMR spectrum consists of two doublets (J = 14 Hz) at δ5.9 and δ7.1. Propose a structure consistent with these data.

Propose a structure that corresponds to each spectrum.

(a) <IMAGE>

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

The spectrum of trans-hex-2-enoic acid follows.

(a) Assign peaks to show which protons give rise to which peaks in the spectrum.

(b) Draw a tree to show the complex splitting of the vinyl proton centered around 7 ppm. Estimate the values of the coupling constants.

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 “equivalent by NMR.”

(a) Use the imaginary replacement technique to show that the two allylic protons (those on C₃) of allyl bromide are enantiotopic.

Predict the theoretical number of different NMR signals produced by each compound, and give approximate chemical shifts. Point out any diastereotopic relationships.

a. 2-bromobutane

b. cyclopentanol

Predict the theoretical number of different NMR signals produced by each compound, and give approximate chemical shifts. Point out any diastereotopic relationships.

c. Ph—CHBr—CH₂Br

d. vinyl chloride

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

(a) acid catalysis.

(b) base catalysis.

Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D₂O.