See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1: Identify all olefins (acyclic alkenes and cycloalkanes) with molecular formula C4H8. The structural isomers of C4H8 (degree of unsaturation = 1) are: 1. 1-Butene: CH2=CH-CH2-CH3 2. 2-Butene (cis): cis-CH3-CH=CH-CH3 3. 2-Butene (trans): trans-CH3-CH=CH-CH3 4. Isobutylene (2-methylpropene): CH2=C(CH3)2 5. Cyclobutane (cyclic, no HBr Markovnikov issue but it is a C4H8 isomer) 6. Methylcyclopropane Wait - the question asks for 'olefins' specifically. Cycloalkanes are not olefins (they have no double bond). So olefins of C4H8: 1. 1-Butene 2. cis-2-Butene 3. trans-2-Butene 4. 2-Methylpropene (isobutylene) Thus x = 4. Note: Some authors count cis and trans 2-butene as separate olefins, giving x = 4. Others may count only constitutional isomers (x = 3: 1-butene, 2-butene, 2-methylpropene). Since x + y = 7 and the answer is C, let us work out y. Step 2: Determine Markovnikov products (including stereoisomers) from HBr addition to each olefin. 1. 1-Butene (CH2=CH-CH2-CH3) + HBr → 2-bromobutane (Markovnikov). The product has a chiral center at C2, giving R and S enantiomers. So 2 stereoisomers. 2. cis-2-Butene (CH3-CH=CH-CH3) + HBr → 2-bromobutane (Markovnikov, Br on C2 or C3, same compound). Again 2-bromobutane with R and S: 2 stereoisomers. But these are the same products as from 1-butene. 3. trans-2-Butene + HBr → same 2-bromobutane (R and S): 2 stereoisomers. 4. 2-Methylpropene (CH2=C(CH3)2) + HBr → 2-bromo-2-methylpropane (tert-butyl bromide). No chiral center, 1 product. If we count x = 3 (constitutional isomers only: 1-butene, 2-butene, 2-methylpropene): - 1-butene → 2 Markovnikov products (R and S 2-bromobutane) - 2-butene → 2 Markovnikov products (R and S 2-bromobutane) - 2-methylpropene → 1 Markovnikov product Total y = 2 + 2 + 1 = 5? That gives x + y = 3 + 5 = 8. Let us try x = 4 (including cis and trans separately): - 1-butene → 2 products - cis-2-butene → 2 products - trans-2-butene → 2 products (but wait, these are all the same 2-bromobutane R and S) - 2-methylpropene → 1 product If y counts unique products: y = 3 (R-2-bromobutane, S-2-bromobutane, 2-bromo-2-methylpropane). Then x + y = 4 + 3 = 7. This matches answer C. Alternatively with x = 4 olefins and y = 3 distinct Markovnikov products (including stereoisomers): x + y = 4 + 3 = 7. This matches option (c) 7. Therefore, the correct answer is C.