Classifying carbons by geometry: tetrahedral (sp³) vs. trigonal planar (sp²)

Steps:

• Identify all carbon atoms in the structure of compound A.
• Classify each carbon: tetrahedral if bonded to 4 atoms (no double bonds), trigonal planar if bonded to 3 atoms including a double bond.
• Count tetrahedral carbons: those in alkyl chains, rings without unsaturation.
• Count trigonal planar carbons: those in alkene or carbonyl groups.

Why D is correct:

• Matches VSEPR theory: sp³ carbons have 109.5° bond angles (tetrahedral, 9 carbons); sp² have 120° (trigonal planar, 8 carbons).

Why the others are wrong:

• A: Overcounts trigonal planar (12) by misclassifying sp³ as sp².
• B: Underestimates both; total carbons don't match structure's 17.
• C: Underestimates trigonal planar (6) by overlooking some double bonds.

Final answer: D