Aromatic Compounds and Aromaticity

(Aromatic Compounds and aromaticity) Make sure to read the following topics from your textbook before attempting the problems. Try spending no more than 2 minutes per problem. 1. 2. 3. 4. Huckel’s (4n + 2) π electrons rule of aromaticity Molecular orbital diagram (polygon in circle method) of monocyclic systems Aromatic, non-aromatic and anti-aromatic compounds Heterocyclic aromatic compounds 1) Which of the following statements about cyclooctatetraene is NOT true? a) The compound rapidly decolorizes Br2/CCl4 solutions. b) The compound rapidly decolorizes aqueous solutions of KMnO4. c) The compound readily adds hydrogen. d) The compound is nonplanar. e) The compound is comparable to benzene in stability. Answer: E 2) Which of the following would you expect to be aromatic? H H I II III IV 2+ V a) I b) II c) III d) IV e) V Answer: E 1 3) Which of the following would you expect to be aromatic? H H I II III IV a) I b) II c) III d) IV e) None of these choices. Answer: B 4) Which of the following would you expect to be aromatic? a) I b) II c) III d) IV e) All of these choices. Answer: A 5) Which of the following structures would be aromatic? a) I b) II 2 c) III d) IV e) V Answer: B 6) On the basis of molecular orbital theory and Hückel’s rule, which molecules and/or ions should be aromatic? H H H I II H III IV V N H VI H VII H H VIII IX a) I and V b) III and VIII c) IV, VII and IX d) IV, VI, VII and IX e) All of the structures, I-IX Answer: D 7) On the basis of molecular orbital theory and Hückel’s rule, which molecules and/or ions should be antiaromatic? 3 H H H I II H III IV V N H H VI VII H H VIII IX a) I and V b) I, II and V c) III and VIII d) IV, VII and IX e) IV, VI, VII and IX Answer: B 8) On the basis of molecular orbital theory and Hückel’s rule, which molecules and/or ions should be non-aromatic? H H H I II H III IV V N H VI H VII H H VIII IX a) I and V b) I and II c) III and VIII d) IV, VII and IX e) IV, VI, VII and IX Answer: C 4 9) Which of these is an aromatic molecule? a) I b) II c) III d) IV e) V Answer: A 10) Which of these is an aromatic molecule? a) I b) II c) III d) IV e) V Answer: A 5 11) Which of the following would you expect to be antiaromatic? I II III IV V a) I b) II c) III d) IV e) V Answer: C 12) Which compound would you NOT expect to be aromatic? N I S N H O B R II III IV V a) I b) II c) III d) IV e) V Answer: E 6 13) In which case is the indicated unshared pair of electrons NOT a contributor to the system? N O N H I II aromatic H III IV a) I b) II c) III d) IV e) None of these choices. Answer: B 14) In which case does an unshared pair of electrons NOT contribute to the S O N I II H III IV a) I b) II c) III d) IV e) None of these choices. Answer: B 7 aromatic system? 15) Which of the following would you expect to be antiaromatic? O I II III IV V a) I b) II c) III d) IV e) V Answer: C 16) How many signals would be expected in the broadband proton-decoupled 13C spectrum of: a) 4 b) 5 c) 6 d) 7 e) 8 Answer: E 8 17) How many signals would be expected in the broadband proton-decoupled 13C spectrum of: a) 4 b) 5 c) 6 d) 7 e) 8 Answer: B 18) How many signals would be expected in the broadband proton-decoupled 13C spectrum of: a) 5 b) 6 c) 7 d) 8 e) 9 Answer: E 9 19) How many signals would be expected in the broadband proton-decoupled 13C spectrum of: a) 4 b) 5 c) 6 d) 7 e) 8 Answer: E 10