Electron affinities (EA) were determined experimentally. For COT, EA was
obtained from the forward and reverse reaction rate constants for the
electron-transfer
equilibrium between COT and O_{2}^{-}. The EAs of
C_{8}H_{6}
and C_{8}H_{7} were obtained using photoelectron
spectroscopy
of C_{8}H_{6}^{-} and
C_{8}H_{7}^{-}.
The authors used MO calculations to investigate the structures
of
C_{8}H_{7}^{-} and C_{8}H_{7}.
The thermodynamic acidities (DH_{acid})
of C_{8}H_{9},
C_{8}H_{8}, and C_{8}H_{7}
were bracketed by proton-transfer reactions of the corresponding anions.
Bond dissociation energies (BDE) for C_{8}H_{n }(n=7-9)
were obtained from EA and DH_{acid}
using the following relation:

In addition, BDE of C_{8}H_{10}
were determined by this equation:

RH |
DH_{acid}(kcal/mol) |
EA(eV) |
BDE(R-H) (kcal/mol) |

C_{8}H_{10} |
82.6 +(or-) 3.8 | ||

C_{8}H_{9} |
-349.9+(or-)4.1 | 49.1+(or-)4.1 | |

C_{8}H_{8} |
381.3+(or-)2.3 | 0.55+(or-)0.02 | 93.0+(or-)2.3 |

C_{8}H_{7} |
357.2+(or-)8.3 | 1.091+(or-)0.008 | 67.8+(or-)8.3 |

C_{8}H_{6} |
1.044+(or-)0.008 |

1. (SCL) Give the definition of adiabatic electron affinity (EA). Why
does
the large conformational change between the ground states of COT and COT
^{- }make the determination of adiabatic EA difficult?

2. (SCL) What reactions form the basis of equation (1) and equation (2)?

3. (RQD) Explain the comparatively low EA value for C_{8}H_{8
}(see Table 1).

4. (RQD) Explain the trend in column 3 of Table 1.

5. (FAR) The rearrangement product of COT ^{-} was
predicted
basing on the MO calculation unspecified in the paper. What kind of
calculation
would you do to predict this structure?

The group met 2 times on the first week of February in order to select the paper. First we met in 324 Chemistry to discuss the type of paper required (it took about 15-20 minutes) and then in 115 Chemistry for final selection. We browsed through communications in 1996-97 JACS and Angewante Chemie looking for the papers related to the computational chemistry. We found about a dozen of papers and selected this one. This meeting took about an hour.

Then we met on February 14 in 324 Chemistry to write the problems. We spent about an hour discussing and writing problems. Then Lixin transferred the assignment into an HTML file. We met on February 15 and spent 1.5 hours correcting the mistakes and finishing up the assignment.

As for our experiences, we feel that it was beneficial to do the assignment in the group. Possibility to divide work between partners saved some time. Discussions within the group were also quite helpful both in the identification of the suitable paper and in the creation of problems.

The biggest problem we encountered was to find the suitable paper. Insufficient background in computational chemistry also made life harder.

Our work together didn't go beyond the project. But we find the projects of this kind quite helpful.