15. Analytical Techniques:IR, NMR, Mass Spect

Which of the labeled hydrogens will be most de-shielded?

Which compound possesses a hydrogen with the highest chemical shift for its 1H NMR signal?

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

(c) CH₃–O–CH₂CH₂CH₂Cl

(d) CH₃CH₂–C≡C–H

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.

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

(a)

(b)

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?

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.

h.

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.

e.

Label each set of chemically equivalent protons, using a for the set that will be at the lowest frequency in the ¹H NMR spectrum, b for the next lowest, and so on. Indicate the multiplicity of each signal.

a.

Explain the relative chemical shifts of the benzene ring protons in Figure 14.18.

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Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.

c. ClCH₂CH₂CH₂Cl

Explain why the chemical shift of the OH proton of a carboxylic acid is at a higher frequency than the chemical shift of an OH proton of an alcohol.

Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?

a.

b.

Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?

c.

d.