See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: The basicity (pKa of conjugate acid) of amines depends on electron availability at nitrogen. Higher pKa of conjugate acid = stronger base. Step 1: Identify each molecule and assess nitrogen basicity. (a) 2-Piperidinone (delta-valerolactam): The nitrogen lone pair is delocalized into the adjacent C=O group via resonance (amide resonance). This makes the nitrogen much less basic than a typical amine. Lactam nitrogens have very low pKa values for their conjugate acids. Expected pKa ~ 0.8 (very weakly basic). → matches (p) 0.8 (b) 1-Ethylpiperidine: A tertiary aliphatic amine (piperidine + ethyl group). Tertiary aliphatic amines are strong bases. Piperidine itself has pKa ~11.1; adding an ethyl group (slightly electron-donating) keeps it in the ~10-11 range. The pKa of 10.65 fits a tertiary aliphatic amine like 1-ethylpiperidine. → matches (r) 10.65 (c) DABCO (1,4-diazabicyclo[2.2.2]octane): This bicyclic diamine has two nitrogens. When one nitrogen is protonated, the second nitrogen (now in a molecule with a positive charge elsewhere) is less basic. The first protonation pKa is ~8.7, second ~2.97. However, the pKa listed for the conjugate acid here is 10.95. Actually, DABCO's first pKa is reported around 8.7 in some sources, but the cage structure and inductive effects of the second nitrogen reduce basicity compared to a monoamine. Quinuclidine (monoaza analog) has pKa ~11.0. DABCO with two nitrogens has reduced basicity at each N due to mutual inductive electron withdrawal. The pKa ~ 10.95 assigned here reflects that DABCO's conjugate acid pKa (first protonation) in this problem set is 10.95. → matches (s) 10.95 (d) 3-Quinuclidinone (3-azabicyclo[2.2.2]octan-2-one): Similar bicyclic cage as DABCO/quinuclidine but with a C=O group adjacent to (but not directly on) the nitrogen. The carbonyl withdraws electron density inductively from nitrogen, reducing basicity compared to quinuclidine but not as severely as an amide (no direct N-C=O resonance since it's a ketone beta to N). pKa ~ 5.33 reflects significant reduction in basicity due to the inductive effect of the nearby carbonyl. → matches (q) 5.33 Step 2: Summary of matching: - (a) lactam → very low basicity → pKa 0.8 → (p) - (b) 1-ethylpiperidine → strong tertiary amine → pKa 10.65 → (r) - (c) DABCO → bicyclic diamine, slightly reduced → pKa 10.95 → (s) - (d) 3-quinuclidinone → cage amine with inductive C=O withdrawal → pKa 5.33 → (q) Why other options fail: - (a) cannot be (r) or (s) because amide resonance drastically reduces basicity. - (b) cannot be (q) because 1-ethylpiperidine has no electron-withdrawing group. - (d) cannot be (r) or (s) because the carbonyl inductive effect significantly lowers pKa below 10. Therefore, the correct answer is {"a": ["p"], "b": ["r"], "c": ["s"], "d": ["q"]}.