Question
The energy of this orbital is equal to the negative first ionization energy according to Koopmans’ theorem. For 10 points each:
[10m] Name this construct that is the (emphasize) lower energy orbital in a pair of molecular orbitals whose energy gap controls the favorability of pericyclic reactions.
ANSWER: highest occupied molecular orbital [or HOMO]
[10e] The HOMO-LUMO gap explains why electron-withdrawing groups point towards each other in this reaction, thus serving as the basis for this reaction’s endo rule. This reaction forms a cyclohexene ring from a diene and a dienophile.
ANSWER: Diels–Alder reaction
[10h] The hexadehydro Diels–Alder reaction is notable for its ability to form this species instead of the standard cyclohexene. Inability to trap this species allows it to dimerize into biphenylene.
ANSWER: benzynes [accept arynes; reject “benzene”]
<Chemistry>
Summary
| 2024 ACF Regionals @ Nebraska | 01/27/2024 | Y | 2 | 15.00 | 100% | 50% | 0% |
| 2024 ACF Regionals @ Imperial | 01/27/2024 | Y | 5 | 10.00 | 60% | 40% | 0% |
Data
| Bristol | Cambridge C | 0 | 0 | 0 | 0 |
| Oxford A | Cambridge A | 10 | 10 | 0 | 20 |
| Edinburgh | Durham A | 0 | 10 | 0 | 10 |
| Imperial A | Imperial B | 10 | 10 | 0 | 20 |
| Sheffield | Oxford B | 0 | 0 | 0 | 0 |