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9 Cards in this Set
- Front
- Back
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Why is cyclopentadiene a better acid than water (i.e., it has a pKa of ~10)? |
Because it's aromatic so its ionic (basic) form is more stable and the more stable the conjugate base, the better the acid |
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What are the 4 main electron donating groups in aromatic reactions, in order of strength, which decrease the homo-lumo gap and thus increase reaction rate? |
O- > NR2 -> RO -> alkyl |
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Why do electron withdrawing group decrease the rate of a reaction? |
They decrease HOMO energy increasing the HOMO-LUMO gap, and making positive charge on the ring which then allows for less electron delocalization and thus a decreased rate |
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Which type of aromatic substituents favor ortho/para configurations? Of the two, which is favored and why? |
Electron donating groups favor ortho and para; para is often most favorable because of steric effects |
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What are the 4 main electron-withdrawing groups? What configuration do they favor? |
NO2, SO2R, CO2R, CHO; favor meta configuration |
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What is the effect of a halogen substituent on an aromatic ring? What configuration do such halogenated aromatic rings prefer? |
It slows down the reaction compared to benzene; ortho/para directed |
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In a case where there is both an electron donating group AND an electron withdrawing group, which predominates in overall configuration during aromatic substitution? |
The electron donating group, favoring ortho/para configuration |
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What are the 3 steps to electrophilic aromatic substitution reactions? |
Generation of the electrophile; nucleophilic reaction of the pi electrons of the aromatic ring with the electrophile to form a resonance-stabilized carbocation intermediate; loss of a proton from the carbocation intermediate to ultimately form the substituted aromatic compound. |
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The _ _ of a substituent group is the ability of the substituent to stabilize the carbocation intermediate in electrophilic substitution by delocalization of electrons from the substituent into the ring. |
Resonance effect |
