Chapter 13: Structure Determination: Nuclear Magnetic Resonance Spectroscopy

Predict the splitting pattern for each kind of hydrogen in the following molecules:

(a) $\left({\mathrm{CH}}_3\right){}_3\mathrm{CH}$

(b)${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CO}}_2{\mathrm{CH}}_3$

(c) trans-2-Butene

Predict the splitting pattern for each kind of hydrogen in isopropyl propanoate,${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}\mathbf{CH}{\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}$.

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:

a.

b.

c.

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:

The acid-catalyzed dehydration of 1-methylcyclohexanol yields a mixture of two alkenes. How could you use ${}^1\mathrm{H}$NMR to help you decide which was which?

How could you use ${}^{\mathbf{1}}\mathbf{H}$NMR to distinguish between the following pairs of isomers?

Propose structures for compounds that fit the following NMR data:

(a) C₅H₁₀O

0.95$\mathrm{\delta }$(6H,double, J = 7Hz)

2.10$\mathrm{\delta }$(3H,singlet)

2.43$\mathrm{\delta }$(1H, mutiplet)

(b) C₃H₅Br

2.32$\mathrm{\delta }$(3H,singlet)

5.35 $\mathrm{\delta }$(3H,singlet)

5.45$\mathrm{\delta }$(1H, broad signet )

Propose structures for the two compounds whose¹H NMR spectra are

shown.

(a) C₄H₉Br

(b) C₄H₈CI₂

How many ₁₃C NMR absorptions would you expect for cis-1,3-dimethylcyclohexane?For trans-1,3-dimethylcyclohexane? Explain.

How many absorptions would you expect to observe in the NMR

spectra of the following compounds?

(a) 1,1-Dimethylcyclohexane

(b) CH₃CH₂OCH₃

(c) tert-Butylcyclohexane

(d) 3-Methyl-1-pentyne

(e) cis-1,2-Dimethylcyclohexane

(f) Cyclohexanone