15. Analytical Techniques:IR, NMR, Mass Spect

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 δ8.0 and 2H triplet at δ4.0

(b) sharp 3H singlet at δ2.0 and 2H quartet at δ4.1

(c) sharp 3H singlet at δ3.7 and 2H quartet at δ2.3

(d) broad 1H singlet at δ11.5 and 2H triplet at δ2.3

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.

<IMAGE>

(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, δ7.1, integral 44 mm

singlet, δ2.3, integral 130 mm

singlet, δ2.2, 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) <IMAGE>

Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, H^a is a singlet, area = 1, at δ2.4.

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.

(a) <IMAGE>

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

<IMAGE>

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