See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: Vinylic hydrogens are H atoms directly attached to sp2 carbons of a C=C double bond. Allylic hydrogens are H atoms on sp3 carbons adjacent (next) to a C=C double bond. The structure shown is 1,3-cyclohexadiene (double bonds at C1-C2 and C3-C4 of the six-membered ring). The molecular formula of 1,3-cyclohexadiene is C6H8. Identifying the carbons: - C1 and C2 are sp2 (part of first double bond), each bears 1 H → 2 vinylic H - C3 and C4 are sp2 (part of second double bond), each bears 1 H → 2 more vinylic H - Total vinylic H = 4 Identifying allylic carbons (sp3 carbons adjacent to a double bond): - C5 is sp3, adjacent to C4 (double bond C3=C4), bears 2 H → 2 allylic H - C6 is sp3, adjacent to C1 (double bond C1=C2), bears 2 H → 2 more allylic H - But C5 and C6 are also adjacent to each other; each is allylic with respect to one double bond. - Total allylic H = 2 + 2 = 4 Note: In 1,3-cyclohexadiene, C5 and C6 are the only two sp3 carbons. Each has 2 H atoms. So allylic H = 4. Why other options fail: - (a) 2 and 2: undercounts both vinylic and allylic H - (c) 2 and 4: undercounts vinylic H - (d) 4 and 2: undercounts allylic H Therefore, the correct answer is B.