15. Analytical Techniques:IR, NMR, Mass Spect

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

An unknown compound (C₇H₆O) gives the IR spectrum shown here. At what chemical shifts would you expect to see signals in the ¹H NMR spectrum?

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

(c) CH₃–O–CH₂CH₂CH₂Cl

(d) CH₃CH₂–C≡C–H

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

a.

b.

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.

Compound A with molecular formula C₆H₁₀ has two peaks in its ¹H NMR spectrum, both of which are singlets (with ratio 9 : 1). Compound A reacts with an acidic aqueous solution containing mercuric sulfate to form compound B, which gives a positive iodoform test (Problem 58) and has an 1H NMR spectrum that shows two singlets (with ratio 3 : 1). Identify A and B.

For the following molecules, give the chemical shift for each indicated hydrogen.

(e)

How would you expect the IR and ¹H NMR spectra for propanamide and N,N-diethylpropanamide to differ?

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

The ¹H NMR chemical shifts of nitromethane, dinitromethane, and trinitromethane are at δ6.10, δ4.33, and δ7.52. Match each chemical shift with the compound. Explain how chemical shift correlates with pK_a.

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.

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

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?

For the following molecules, give the chemical shift for each indicated hydrogen.

(d)