Problem
15-4
![Pyridine has three lobes around nitrogen. One lobe has an unpaired electron and one lobe has a lone pair of electrons. Upper lobe of each carbon has an unpaired electron.]()
Pyridine has an aromatic sextet of electrons.
Problem
15-5
Cyclodecapentaene is not flat because of steric interactions.
Problem
15-6
All C – C bonds are equivalent; one resonance line in both 1H and 13C NMR spectra.
Problem
15-7
The cyclooctatetraenyl dianion is aromatic (ten π electrons) and flat.
Problem
15-10
![The orbital representation of thiazolium ring shows two lobes around sulfur each with a lone pair and upper lobes of the remaining atoms of the ring each with an unpaired electron.]()
The thiazolium ring has six π electrons.
Problem
15-11
![Two resonance structures of azulene, separated by a double-headed arrow.]()
Yes, it's aromatic.
Problem
15-12
The three nitrogens in double bonds each contribute one; the remaining nitrogen contributes two.