15. Analytical Techniques:IR, NMR, Mass Spect

A ¹H NMR spectrum has a singlet at 4.1 ppm with an integration of 2H. How many hydrogen atoms are on the neighboring carbon atom?

A ¹H NMR spectrum contains a quartet at 4.1 ppm integrating to 2H and triplet at 0.9 ppm integrating to 3H, among other signals. What fragment is likely part of this molecule?

Which of the following structures would give the following ¹H NMR spectrum? 0.93 ppm (s, 9H), 2.13 ppm (d, 2H), 9.85 ppm (t, 1H)

Draw the expected NMR spectrum of methyl propionate, and point out how it differs from the spectrum of ethyl acetate.

Each of these four structures has molecular formula C4H8O2. Match the structure with its characteristic proton NMR signals. (Not all of the signals are listed in each case.)

(a) sharp 1H singlet at d 8.0 and 2H triplet at d 4.0 (b) sharp 3H singlet at d 2.0 and 2H quartet at d 4.1 (c) sharp 3H singlet at d 3.7 and 2H quartet at d 2.3 (d) broad 1H singlet at d 11.5 and 2H triplet at d 2.3

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

Sketch your predictions of the proton NMR spectra of the following compounds. (b)

Sketch your predictions of the proton NMR spectra of the following compounds. (a) CH3-O-CH2CH3

The following proton NMR spectrum is of a compound of molecular formula C3H8O.

(a) Propose a structure for this compound. (b) Assign peaks to show which protons give rise to which signals in the spectrum.

An unknown compound has the molecular formula C9H11Br. Its proton NMR spectrum shows the following absorptions: singlet, d7.1, integral 44 mm singlet, d2.3, integral 130 mm singlet, d2.2, integral 67 mm Propose a structure for this compound.

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

Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, Ha is a singlet, area = 1, at d2.4.

Propose chemical structures consistent with the following NMR spectra and molecular formulas. (a) In spectrum (a), explain why the peaks around d1.65 and d3.75 are not clean multiplets, but show complex splitting.

Draw the NMR spectra you expect for the following compounds. (b)

Draw the NMR spectra you expect for the following compounds. (a)

Identify each of the following compounds from its molecular formula and its 1H NMR spectrum: b. C6H12O

Identify each of the following compounds from the 1H NMR data and molecular formula: c. C5H10O2: a 3H triplet at 1.15 ppm a 3H triplet at 1.25 ppm a 2H quartet at 2.33 ppm a 2H quartet at 4.13 ppm

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

Explain how the following compounds, each with the same molecular formula, could be distinguished by their 1H NMR spectra.

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

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

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

Sketch the following spectra that would be obtained for 2-chloroethanol: b. The 1H NMR spectrum for a sample of the alcohol that contains a trace amount of acid.

Sketch the following spectra that would be obtained for 2-chloroethanol: a. The 1H NMR spectrum for an anhydrous sample of the alcohol.

The 1H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.

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

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.)

Identify each of the following compounds from the 1H NMR data and molecular formula: b. C8H9Br: a 3H doublet at 2.01 ppm a 1H quartet at 5.14 ppm a 5H broad singlet at 7.35 ppm

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

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

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

Match each of the 1H NMR spectra with one of the following compounds: b.

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.

Which of the following compounds is responsible for the 1H NMR spectrum shown below?

Identify each compound from its molecular formula and its 1H NMR spectrum: b. C5H10O

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

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

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.

(•••) In the lab, ¹H NMR is often used to verify that a reaction has worked as expected by comparing the product spectrum with what is expected. Given the ¹H NMR of the reactant shown, draw the spectrum you'd expect to see of the product that results.

(•••) (a) Using the ¹H NMR spectra, (b) Provide an arrow-pushing mechanism for the reaction.

Without worrying about the relative location of the signals (i.e., the chemical shift) or the splitting patterns, draw a spectrum of the following molecule, being sure to indicate the integration of each peak. Label each signal based on the set of equivalent hydrogens to which it corresponds. [We expand on this question in future assessments.]

(•••) Draw the ¹H NMR spectrum you would expect to see for each of the molecules in Assessment 15.63. b

(•••) Draw the ¹H NMR spectrum you would expect to see for each of the molecules in Assessment 15.63. c

(•••) Draw the ¹H NMR spectrum you would expect to see for each of the molecules in Assessment 15.63. d

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)

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. (c)

(•••) Assign the peaks in the ¹H NMR spectrum for the molecule shown.

The spectrum shown here is for a molecule with a molecular formula of C₄H₉Cl. Suggest a structure for this molecule.

When a compound with molecular formula C11H14O2 undergoes acid-catalyzed hydrolysis, one of the products that is isolated gives the following 1^H NMR spectrum. Identify the compound.

How many signals would the product of the following reaction show in a. its 1H NMR spectrum? b. its 13C NMR spectrum?

The following NMR spectra correspond to compound of formula (C) C6H10O2. Propose structure, and show how it is consistent with the observed absorptions. (c)

The following NMR spectra correspond to compound of formula (A) C9H10O2. Propose structure, and show how it is consistent with the observed absorptions. (a)

The only organic compound obtained when compound Z undergoes the following sequence of reactions gives the 1H NMR spectrum shown. Identify compound Z.

(b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the '15 to 20 times as large' rule of thumb?

When heated with chromic acid, compound A forms benzoic acid. Identify compound A from its 1H NMR spectrum.

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

(•••) Given the ¹H NMR spectrum and the molecular formula, suggest a structure for each molecule. [The IR spectrum suggests the presence of two C=O bonds.] (a) Important IR bands (cm ⁻ ¹) : 1728, 1708 [Note: The pKₐ of this molecule is around 10.]

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.