See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the structure: The compound shown is a C3-symmetric tricyclic molecule consisting of three benzene rings fused to a central six-membered ring that bears three ketone (=O) groups at alternating carbons (positions 1, 3, 5 of the central ring). This molecule is essentially 10,15-dihydro-5H-tribenzo[a,f,k]trindene-5,10,15-trione (truxenetrione) or a closely related trione. Step 2 - Check for C4 axis (option b): A C4 axis requires 4-fold rotational symmetry (90° rotation gives identical structure). This molecule has 3-fold (C3) symmetry, not 4-fold. Option (b) is incorrect. Step 3 - Check for centre of symmetry / inversion centre (option a): An inversion centre maps every atom at (x,y,z) to (-x,-y,-z). For this planar or near-planar molecule with C3v symmetry, there is no inversion centre because the three carbonyl oxygens are all on the same face (or the molecule has C3v symmetry, not Ci). Option (a) is incorrect. Step 4 - Check chirality (option d): The molecule is NOT chiral because it possesses symmetry elements (mirror planes) that make it achiral. Option (d) is incorrect. Step 5 - Check for plane of symmetry (option c): The molecule has C3v symmetry. It possesses at least one (in fact three) planes of symmetry - each passing through one carbonyl group and the midpoint of the opposite C-C bond of the central ring, bisecting the molecule. Additionally, if the molecule is planar or has a molecular plane, that itself acts as a plane of symmetry. These mirror planes make the molecule achiral and confirm the presence of planes of symmetry. Option (c) is correct. Step 6 - Why other options fail: No C4 axis exists (only C3); no inversion centre exists in a C3v molecule; the molecule is achiral due to its mirror planes. Therefore, the correct answer is C.