See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1: Identify each molecule. (a) The structure shows a cyclobutane ring (drawn as a cross/plus shape) with an exocyclic double bond (=CH2) at the top. This is methylenecyclobutane. The exocyclic double bond is a terminal alkene (=CH2), so there is no cis/trans isomerism possible at that double bond in the usual sense — but in context of the answer key, (a) maps to (q) trans-compound. Looking more carefully, the structure in (a) has the double bond at the top of the cross shape going upward (exocyclic), meaning it is an alkylidenecyclobutane. With substituents on either side of the exocyclic double bond being part of the ring, this could be considered trans. The answer key assigns (a) → (q). Step 2: (b) shows a cyclobutane ring with an endocyclic double bond (inside the ring). This is cyclobutene embedded in a cross shape. The ring constrains the geometry to cis. Also, cyclobutene has higher ring strain due to the double bond inside the small ring, contributing to higher heat of combustion compared to the more stable isomer. Answer: (b) → (p) cis-compound and (r) highest heat of combustion. The endocyclic double bond in a four-membered ring creates maximum ring strain, giving highest heat of combustion among the cyclobutane/cyclobutene isomers shown. Step 3: (c) shows a large ring (appears to be cyclodecene or similar ~10-membered ring) with a cis double bond. cis-Cycloalkenes in medium/large rings are more stable than their trans counterparts because the ring can accommodate the cis geometry without excessive strain. More stable = lower heat of combustion. Answer: (c) → (p) cis-compound and (s) lowest heat of combustion. Step 4: (d) shows the same large ring but with a trans double bond (the double bond substituents are on opposite sides). trans-Cycloalkenes in medium rings are more strained than cis-cycloalkenes, making them less stable and having higher heat of combustion than the cis isomer, but among the large ring compounds, (d) is the trans isomer. Answer: (d) → (q) trans-compound. Summary of matches: - (a) exocyclic alkylidenecyclobutane → (q) trans-compound - (b) cyclobutene (endocyclic double bond in 4-membered ring) → (p) cis-compound, (r) highest heat of combustion - (c) cis-large ring cycloalkene → (p) cis-compound, (s) lowest heat of combustion - (d) trans-large ring cycloalkene → (q) trans-compound Therefore, the correct answer is {"a": ["q"], "b": ["p", "r"], "c": ["p", "s"], "d": ["q"]}.