Q6. Why does NCERT’s list of carcinogens not include naphthalene, although naphthalene is a fused-ring aromatic hydrocarbon?
NCERT’s description covers polynuclear hydrocarbons with more than two fused benzene rings. Naphthalene has only two.
Q7. Show that 1,2,5,6-dibenzanthracene, C22H14, fits five fused benzene rings.
Degree of unsaturation = (44 + 2 − 14)/2 = 16 = rings + π bonds. Five rings leave 11 π bonds, that is 22 π electrons, one for each of the 22 sp2 carbons.
Q8. 3-Methylcholanthrene is C21H16, with four six-membered rings, one five-membered ring containing two CH2 groups, and a methyl group. Check the formula with the degree of unsaturation.
(42 + 2 − 16)/2 = 14 = rings + π bonds. There are 5 rings, and the 18 aromatic carbons (21 minus the two CH2 carbons and the CH3 carbon) give 9 π bonds: 5 + 9 = 14.