Q4. Cyclohexene has a C=C double bond in a ring. Is it an aromatic compound?
No. It is an alicyclic, homocyclic compound: a ring of carbon atoms that behaves like an aliphatic alkene. Having a ring and a double bond does not make a compound aromatic; benzene and its relatives form a special class.
Q5. Write the first three members of the alkanol (alcohol) series, CnH2n+1OH, with their molecular masses (C = 12, H = 1, O = 16).
CH3OH, 32 u; C2H5OH, 46 u; C3H7OH, 60 u. Each differs from the next by CH2, 14 u.
Q6. Which of CH3OH, C2H5OH, CH3OCH3 and C3H7OH belong to the same homologous series?
CH3OH, C2H5OH and C3H7OH: all are alcohols with the –OH group and differ by CH2. CH3OCH3 has the same molecular formula as ethanol, C2H6O, but it is an ether (C–O–C), a different family.
Q7. Classify thiophene, aniline and tetrahydrofuran.
Thiophene: aromatic, heterocyclic (S in the ring). Aniline, C6H5NH2: aromatic, benzenoid. Tetrahydrofuran: non-aromatic heterocyclic (O in a saturated ring); NCERT groups it with alicyclic examples.
Q8. An alkane has a molecular mass of 86 u. Find its molecular formula.
CnH2n+2 has mass 12n + 2n + 2 = 14n + 2. So 14n + 2 = 86 gives n = 6: C6H14 (hexane).