15. Analytical Techniques:IR, NMR, Mass Spect

The ¹H NMR spectra of three isomers with molecular formula C₄H₉Br are shown here. Which isomer produces which spectrum?

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A small pilot plant was adding bromine across the double bond of but-2-ene to make 2,3-dibromobutane. A controller malfunction allowed the reaction temperature to rise beyond safe limits. A careful distillation of the product showed that several impurities had formed, including the one having the NMR spectra that appear below. Determine its structure, and assign the peaks to the protons in your structure.

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The following ¹H NMR spectra are for four compounds, each with molecular formula of C₆H₁₂O₂. Identify the compounds.

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

The ¹H NMR spectra of three isomers with molecular formula C₇H₁₄O are shown here. Which isomer produces which spectrum?

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Draw a spectrum for each of the following molecules, being sure to indicate the multiplicity, integration, and chemical shift of each peak. Label each signal based on the set of equivalent hydrogens to which it corresponds.

(b)

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds.

(a) 1-bromopropane and 2-bromopropane

Propose structures that are consistent with the following spectra. (Integral ratios are given from left to right across the spectrum.)

b. The ¹H NMR spectrum of a compound with molecular formula C₆H₁₀O₂ has two singlets with integral ratios of 2 : 3.

Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a), explain why the peaks around δ1.65 and δ3.75 are not clean multiplets, but show complex splitting.

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When compound A (C₅H₁₂O) is treated with HBr, it forms compound B (C₅H₁₁Br). The ¹H NMR spectrum of compound A has a 1H singlet, a 3H doublet, a 6H doublet, and two 1H multiplets. The ¹H NMR spectrum of compound B has a 6H singlet, a 3H triplet, and a 2H quartet. Identify compounds A and B.

Five proton NMR spectra are given here, together with molecular formulas. In each case, propose a structure that is consistent with the spectrum.

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The following ¹H NMR spectra are for four compounds, each with molecular formula of C₆H₁₂O₂. Identify the compounds.

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Describe the ¹H NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals:

g. CH₃CH₂OCH₂CH₃

An alkyl halide reacts with an alkoxide ion to form a compound whose ¹H NMR spectrum is shown here. Identify the alkyl halide and the alkoxide ion. (Hint: See Section 9.15.)

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