See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Base strength of nitrogen compounds depends on: (1) availability of the lone pair on nitrogen, (2) hybridization (sp3 > sp2 > sp), (3) resonance delocalization (reduces basicity), (4) inductive effects of substituents. --- Part (a): Pyridine, 1-methylpyrrolidine, 2-piperidinone (lactam), 4-nitroaniline --- Concepts applied: - 1-methylpyrrolidine: sp3 N, no resonance, alkyl group donates electrons → strongest base (rank 1) - Pyridine: sp2 N, lone pair in sp2 orbital (not in aromatic pi system), moderately basic (rank 2) - 4-nitroaniline: aromatic amine with strong electron-withdrawing nitro group para → very weak base (rank 3) - 2-piperidinone (lactam): N lone pair delocalized into C=O, amide N → weakest base (rank 4) Order of base strength: 1-methylpyrrolidine (1) > pyridine (2) > 4-nitroaniline (3) > 2-piperidinone (4) Assigned ranks: pyridine=2, 1-methylpyrrolidine=1, 2-piperidinone=4, 4-nitroaniline=3 → [2,1,4,3] --- Part (b): Piperidine, Aniline, 4-nitroaniline, Succinimide --- - Piperidine: sp3 N, saturated ring, no resonance → strongest base (rank 1) - Aniline: aromatic amine, lone pair partially delocalized into ring, but no EWG → moderately basic (rank 2) - 4-nitroaniline: aniline with para-NO2, strong EWG reduces lone pair availability further (rank 3) - Succinimide: N flanked by two C=O groups, lone pair extensively delocalized into both carbonyls → weakest base (rank 4) Assigned ranks: piperidine=1, aniline=2, 4-nitroaniline=3, succinimide=4 → [1,2,3,4] --- Part (c): N,N-dimethylaniline, Pyrrole, 1,4,5,6-tetrahydropyrimidine (amidine/guanidine-type), 1-methylpyrrolidine --- - 1,4,5,6-tetrahydropyrimidine / cyclic amidine (guanidinium-type structure): the compound shown is a cyclic guanidine or amidine where conjugation upon protonation stabilizes the conjugate acid by resonance across multiple nitrogens → extremely strong base, strongest (rank 1) - 1-methylpyrrolidine: sp3 N, tertiary, alkyl-substituted → very strong base (rank 2) - N,N-dimethylaniline: tertiary amine but lone pair delocalized into aromatic ring → moderately weak base (rank 3) - Pyrrole: lone pair part of aromatic 6π system, extremely poor base (rank 4) Assigned ranks: N,N-dimethylaniline=3, pyrrole=4, cyclic guanidine/amidine=1, 1-methylpyrrolidine=2 → [3,4,1,2] --- Part (d): Isobutyronitrile, Pyridine, 3-pyrroline (or 2H-pyrrole with N-H), Piperidine --- - Piperidine: sp3 N, saturated ring → strongest base (rank 1) - Pyridine: sp2 N, moderately basic (rank 2) - Isobutyronitrile ((CH3)2CH-CN or (CH3)2C=C=N type): nitrile N is sp hybridized, lone pair in sp orbital, very weakly basic, but slightly more basic than pyrrole-type (rank 3) - 3-pyrroline with N-H (or 2H-pyrrole): N lone pair involved in partial conjugation/aromaticity or allylic delocalization → very weak base (rank 4) Assigned ranks: isobutyronitrile=3, pyridine=2, 3-pyrroline=4, piperidine=1 → [3,2,4,1] Therefore, the correct answer is {"a": [2, 1, 4, 3], "b": [1, 2, 3, 4], "c": [3, 4, 1, 2], "d": [3, 2, 4, 1]}.