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Chapter 16: PROBLEM 16.38b (page 840)

Question: For each NMR spectrum, propose a structure consistent with the spectrum and the additional information provided.

a. Elemental analysis shows the molecular formula to be C8H7OCl . The IR spectrum shows a moderate absorption at 1602 cm-1 and a strong absorption at 1690 cm-1 .

b.The mass spectrum shows a double molecular ion of ratio 1:1 at m/z 184 and 186.

Short Answer

Expert verified

Answer

b. The structure for the given NMR spectrum is given below.

Step by step solution

01

Molecular ion peak

A molecular ion peak is formed when an electron is removed from a neutral compound.This ion helps us determine the molar mass as the electron mass is smaller than the molecule mass.

02

Structure determination

b. The double molecular ion peak of 1:1 intensity at 184 and 186 shows the presence of a bromine atom. When 79 is subtracted from m/z 184, the mass comes to 105 for the rest of the molecule. The rest of the molecule contains a benzene ring plus two carbons and a few hydrogen atoms. There are four aromatic hydrogens in the para pattern (two doublets) as shown by NMR, indicating para-disubstituted benzene. The 2H quartet and 3H triplet suggest that it is an ethyl group.

Structure for the NMR spectrum

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Most popular questions from this chapter

Classify the following compounds as aromatic, antiaromatic, or nonaromatic

(a)

(b)

(c)

(d)

Question: The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

a. Use resonance forms to show the delocalization (over four carbon atoms) of the positive charge, unpaired electron, and negative charge of the benzyl cation, radical, and anion.

b. Toulene reacts with bromine in the presence of light to give benzyl bromide. Propose a mechanism for this reaction.

c. Which of the following reactions will have the faster rate and give the better yield? Use a drawing of the transition state to explain your answer.

Does the MO energy diagram of cyclooctatetraene appear to be a particularly stable or unstable configuration? Explain

Question: For each NMR spectrum, propose a structure consistent with the spectrum and the additional information provided.

a. Elemental analysis shows the molecular formula to be C8H7OCl . The IR spectrum shows a moderate absorption at 1602 cm-1 and a strong absorption at 1690 cm-1 .

b. The mass spectrum shows a double molecular ion of ratio 1:1 at m/z 184 and 186.

The following hydrocarbon has an unusually large dipole moment. Explain how a large dipole moment might arise

(a)Cyclopnonatetraene cation

(b) Cyclononatetraene anion

(c) [16] annulene dianion

(d) [18] annulene dianion

(e)

(f) [20] annulene dication
See all solutions

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