91Ó°ÊÓ

Thiamin, or vitamin B1, contains a positively charged five-membered nitrogen–sulfur heterocycle called a thiazolium ring. Explain why the thiazolium ring is aromatic.

Azulene, a beautiful blue hydrocarbon, is an isomer of naphthalene. Is azulene aromatic? Draw a second resonance form of azulene in addition to that shown.

How many electrons does each of the four nitrogen atoms in purine contribute to the aromatic system?

Give IUPAC names for the following substances (red 5 O, blue 5 N):

All-cis cyclodecapentaene is a stable molecule that shows a single absorption in its NMR spectrum at $\mathbf{5}\mathbf{.}\mathbf{67}\mathit{δ}$. Tell whether it is aromatic, and explain its NMR spectrum.

Give IUPAC names for the following compounds

a)

Give IUPAC names for the following compounds

b)

Propose structures for aromatic hydrocarbons that meet the following descriptions:

(a) C₉H₁₂; gives only one C₉H₁₁Brproduct on substitution of hydrogen on the aromatic ring with bromine

(b)C₁₀ H₁₄; gives only one C₁₀H₁₃Clproduct on substitution of hydrogen on the aromatic ring with chlorine

(c) C₈H₁₀; gives three C₈H₉Brproducts on substitution of hydrogen on the aromatic ring with bromine

(d)C₁₀ H₁₄ ; gives two C₁₀H₁₃Clproducts on substitution of hydrogen on the aromatic ring with chlorine

Look at the three resonance structures of naphthalene shown in Section 15-6, and account for the fact that not all carbon-carbon bonds have the same length. The C1–C2 bond is 136 pm long, whereas the C2–C3 bond is 139 pm long

Anthracene has four resonance structures, one of which is shown. Draw the other three

Anthracene