See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 – Structure of o-xylene and its double bonds. o-Xylene is 1,2-dimethylbenzene. The benzene ring has three formal double bonds (in one Kekulé structure they are at positions 1-2, 3-4, and 5-6; in the other they are at 2-3, 4-5, and 6-1). For ozonolysis purposes, we consider all three double bonds of the ring being cleaved. Step 2 – Numbering and labeling carbons. Label the ring carbons 1–6 with methyl groups at C1 and C2. The three double bonds in one Kekulé form: C1=C2, C3=C4, C5=C6. In the other Kekulé form: C2=C3, C4=C5, C6=C1. Step 3 – Products from ozonolysis (reductive workup with Zn). Each C=C bond is cleaved to give two carbonyl fragments. The substitution at each carbon determines whether the fragment is an aldehyde (CHO) or a ketone (C=O with two carbons attached). - C1 bears a methyl group → upon cleavage gives a CH3-C(=O)- fragment (ketone end). - C2 bears a methyl group → upon cleavage gives a CH3-C(=O)- fragment (ketone end). - C3, C4, C5, C6 bear only H → upon cleavage give -CHO fragments (aldehyde end). Step 4 – Possible dicarbonyl fragments from the ring opening. Since the ring is cleaved at all three double bonds, the ring opens to give a single open-chain hexanedial-type compound, which then further fragments. The adjacent carbons in the ring that are connected give the following paired carbonyl units: - From C1=C2 cleavage: CH3-CO- | -CO-CH3 → diacetyl (option c) is possible. - From C1-C6 and C2-C3 region: CH3-CO- | -CHO and CH3-CO- | -CHO → methylglyoxal (option b) is possible. - From C3=C4 and C5=C6 cleavage: OHC- | -CHO → glyoxal (option a) is possible. Step 5 – Evaluating option (d). Option (d) is CH3-C(=O)-C(=O)-CHO (a compound with a methyl ketone, a second ketone carbonyl, and an aldehyde on the same 3-carbon chain, i.e., 2,3-dioxobutanal or 3-oxobutanal-type). For this fragment to form, we would need a carbon bearing a methyl group directly bonded to a carbon bearing only H in the ring, AND that second carbon would need to be bonded to another carbonyl carbon that is also adjacent to another CHO. Tracing the ring: C1(CH3)-C2(CH3)-C3(H)-C4(H)-C5(H)-C6(H). For the fragment CH3CO-CO-CHO, we would need C bearing CH3 adjacent to C bearing CH3 adjacent to C bearing H cleaved in a specific way, but since C1 and C2 are both methyl-bearing, the C1–C2 cleavage gives CH3CO–COCH3 not CH3CO–CO–CHO. A fragment CH3CO-CO-CHO would require a methyl-bearing carbon adjacent to another carbonyl carbon that is adjacent to an H-bearing carbon in a single fragment, which is not consistent with the connectivity of o-xylene. The fragment would require the same carbon to simultaneously be part of two different cleavage products, which is not possible. Thus, option (d) cannot be obtained. Step 6 – Conclusion. Options (a), (b), and (c) are all legitimate ozonolysis products of o-xylene. Option (d), CH3-C(=O)-C(=O)-CHO, cannot be obtained because no such connectivity exists in the o-xylene ring that would produce a three-carbon fragment with methyl ketone, internal ketone, and terminal aldehyde simultaneously. Therefore, the correct answer is D.