Due Monday, 2/10 at 4pm Problem Set #1, 5.12 Spring 2003 3 pts. Draw out valid Lewis structures (lines or dots) for the following formulas that have ionic bonds. (Show lone pairs and formal charges.) NaHCO₃ [CH₃CH₂OCH₂]⁺ C₂H₂ LiN[CH(CH₃)₂]₂ 2 pts. Draw a valid Lewis structure for AlF₃. Would you expect the aluminum atom to be electrophilic or nucleophilic? Why? Aluminum, like boron, only starts with three valence electrons. This means that the aluminum atom in AlF₃ has six valence electrons and an empty p-orbital. It can accept electrons. The aluminum atom is electrophilic. 3. (3 points) You learned in lecture that phenol is more acidic than cyclohexanol because its conjugate base (phenoxide ion) is stabilized by resonance. Strong acids have stable conjugate bases. a) Draw the relevant resonance structures for the conjugate bases of A and B. b) Which would you expect to be more acidic? Why? A: NO₂ OH NO₂ O⁻ B: O₂N OH O₂N O⁻ b) B is more acidic because of the extra resonance structure that puts the negative charge on the nitro oxygen. In other words, B is more acidic because the conjugate base is more stable (more delocalization = more stabilization). 4. Circle the following pairs of structures that do not constitute resonance structures. For the proper resonance pairs, draw curved arrows to convert the first structure to the second. Draw in all lone pairs that you move. 5. a) Draw all of the relevant resonance structures for A, and rank them by energy (1 = lowest energy). If two or more resonance structures are similar in energy, give them the same ranking. A: H₃C-CH₂-CH₂-CH₂-NH₂ H₃C-CH₂-CH=CH-NH₃⁺ H₃C-CH=CH-CH₂-NH₃⁺ H₂C=CH-CH₂-CH₂-NH₃⁺ H₂C=CH-CH=CH-NH₂ H₂C=CH₂-CH₂-CH₂-NH₂ (Energy: A < B = C < E = F < D) b) Label the electrophilic atoms in A. H₃C-CH₂-CH₂-CH₂-NH₂ H₃C-CH₂-CH=CH-NH₃⁺ H₃C-CH=CH-CH₂-NH₃⁺ H₂C=CH-CH₂-CH₂-NH₃⁺ H₂C=CH-CH=CH-NH₂ H₂C=CH₂-CH₂-CH₂-NH₂ *** = electrophilic** c) Draw all of the relevant resonance structures for B, and rank them by energy (1 = lowest energy). If two or more resonance structures are similar in energy, give them the same ranking. B: H₃C-CH₂-CH₂-O-CH₃ H₃C-CH₂-CH=O⁺-CH₃ H₃C-CH=O-CH₂-CH₃ H₂C=CH-CH₂-O-CH₃ H₂C=CH-CH=O⁺-CH₃ H₂C=CH₂-CH₂-O-CH₃ (Energy: B < E < C < D) d) Label the nucleophilic atoms in B. H₃C-CH₂-CH₂-O-CH₃ H₃C-CH₂-CH=O⁺-CH₃ H₃C-CH=O-CH₂-CH₃ H₂C=CH-CH₂-O-CH₃ H₂C=CH-CH=O⁺-CH₃ H₂C=CH₂-CH₂-O-CH₃ *** = nucleophilic**