See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

To match each Newman projection with the correct conformer name, we analyze the dihedral angles and eclipsing relationships between substituents on the front and back carbons. Concept: In Newman projections, 'eclipsed' means front and back bonds overlap (0° dihedral), 'staggered' means they are 60° apart, 'gauche' is a staggered conformation with 60° between two large groups, and 'anti' is staggered with 180° between large groups. (a) Analysis: The front carbon bears CH3 and CH3 (two methyls together at top) plus two H's, and the back carbon also has H, H, H arranged such that the two CH3 groups on the front are directly eclipsing each other or eclipsing H's — specifically, both methyls on the front carbon eclipse bonds on the back, and looking at the drawing the CH3CH3 are at the top eclipsing each other with all three pairs of bonds overlapping. This represents the highest energy eclipsed conformation where the two largest groups (both CH3) eclipse each other. This is the Fully eclipsed conformation. → matches (p). (b) Analysis: The front carbon has H and CH3 (one methyl, one H at top), and CH3 and H at lower-left. The back carbon has H eclipsing CH3 and H eclipsing H in some pairs. There is a mixture: one CH3 eclipses CH3 and one CH3 eclipses H, meaning not all large groups eclipse large groups, so it is partially eclipsed (some H-H eclipsing and some H-CH3 eclipsing). This is the Partially eclipsed conformation. → matches (q). (c) Analysis: The front carbon has CH3 at top, H at upper-right, H at left; the back carbon has CH3 at bottom, H at lower-left, H at lower-right. The CH3 on front is at top and CH3 on back is at bottom — they are 180° apart (anti). All bonds are staggered (60° between each pair). This is the anti staggered conformation, which is simply called Staggered (specifically anti-staggered, the most stable). → matches (s). (d) Analysis: The front carbon has CH3 at upper-left and CH3 at upper-right (two methyls), H at bottom; the back carbon has H at bottom, H at left, H at right — all staggered. The dihedral angle between the two CH3 groups is 60° (gauche relationship). This is the Gauche staggered conformation. → matches (r). Why other options fail: - (a) cannot be gauche or staggered because bonds are clearly overlapping (eclipsed) and both large groups coincide. - (b) cannot be fully eclipsed because not all large groups eclipse large groups, nor staggered because bonds do overlap. - (c) cannot be gauche because the methyls are 180° apart, not 60°. - (d) cannot be eclipsed because the bonds are clearly staggered (no overlap shown). Therefore, the correct answer is a-p; b-q; c-s; d-r.