Structure and Bonding -- Practice Problems
Structure and Bonding — Practice Problems
10 MCQ questions covering hybridization, resonance, stereochemistry (R/S, E/Z), conformational analysis, and aromaticity. Select an option to check your answer and view the explanation.
Hybridization and Resonance
Stereochemistry and Conformational Analysis
Intuition
Molecular structure determines reactivity: The three-dimensional shape of a molecule, its stereochemistry, determines how it interacts with enzymes, receptors, and other molecules. A molecule with the wrong stereochemistry can be inactive or even toxic.
Why it matters: Drug companies must synthesise the correct enantiomer (mirror-image form) because the wrong one can cause birth defects (as happened with thalidomide). Stereochemistry is not academic, it has life-or-death consequences.
The key insight: Chirality (handedness) matters because biological systems are chiral, enzymes and receptors distinguish between left-handed and right-handed molecules just as your left hand fits only the left glove.
Common Mistakes
Confusing E/Z with cis/trans nomenclature: Cis/trans describes the relative position of identical groups on a double bond. E/Z uses Cahn-Ingold-Prelog priority rules and works for all cases, including when all four substituents are different. Always use E/Z when there are four different substituents, cis/trans becomes ambiguous.
Misapplying Markovnikov’s rule: Markovnikov’s rule states that in HX addition to alkenes, H adds to the carbon with more H atoms. However, this fails for hydroboration-oxidation (anti-Markovnikov) and for additions involving carbocation rearrangements. Always consider whether rearrangements are possible before predicting the product.
Confusing resonance with tautomeric equilibrium: Resonance structures differ only in electron placement, the nuclei stay in the same positions. Tautomers are structural isomers that differ in the position of a hydrogen atom and a double bond (keto-enol tautomerism). They are different molecules in equilibrium, not resonance contributors.