See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the compound: The flat structure shows a 1,4-disubstituted cyclohexane with a methyl group at C1 (bold/wedge, pointing up) and an ethyl group at C4 (bold/wedge, pointing down-right). Both wedge bonds on opposite carbons pointing in opposite directions of the flat drawing indicate a trans-1-methyl-4-ethylcyclohexane. Wait - looking again, both substituents appear to be on wedge bonds (bold), which in a flat cyclohexane means both are on the same face, making this cis-1-methyl-4-ethylcyclohexane. Step 2 - Determine stereochemistry: In the flat hexagon, the methyl at C1 is on a wedge (above plane) and the ethyl at C4 is on a wedge (above plane). Since C1 and C4 are on opposite ends of the ring, both substituents pointing the same direction (both up) in the flat representation means they are CIS to each other. Step 3 - Chair conformations of cis-1-methyl-4-ethylcyclohexane: In a cis-1,4-disubstituted cyclohexane, the two substituents are either both axial or both equatorial in any given chair conformation. When both are equatorial, they are both equatorial but on opposite axial/equatorial positions of the ring - this is allowed for cis-1,4. Step 4 - Stability analysis: The most stable chair conformation places both substituents in equatorial positions, minimizing 1,3-diaxial interactions. For cis-1,4-disubstituted cyclohexane, one chair has both groups equatorial and the other has both groups axial. Both equatorial is far more stable. Step 5 - Identify option B: Option (b) shows the chair conformation where both the methyl (smaller) and ethyl (larger) groups are equatorial. This is the most stable conformation because both groups avoid the large 1,3-diaxial strain. Step 6 - Eliminate other options: Option (a) shows both groups axial - very unstable due to 1,3-diaxial interactions from both substituents. Option (c) appears to show a different arrangement. Option (d) is not a valid chair conformation. Therefore, the correct answer is B.