## oxalate dianion, C2O4-2

 O3 O6 \\ // C1 - C2 = O5 // O4
The ion charge is -2.

## Atomic Charges and Dipole Moment

C1 charge= 0.670
C2 charge= 0.668
O3 charge=-0.835
O4 charge=-0.834
O5 charge=-0.834
O6 charge=-0.834
with a dipole moment of 0.00664 Debye

## Bond Lengths:

between C1 and C2: distance=1.571 ang___ between C1 and O3: distance=1.286 ang___
between C1 and O4: distance=1.286 ang___ between C2 and O5: distance=1.286 ang___
between C2 and O6: distance=1.286 ang___ between O3 and O4: distance=2.289 ang___
between O5 and O6: distance=2.288 ang___

## Bond Angles:

for O3-C1-C2: angle=117.2 deg___ for O4-C1-C2: angle=117.0 deg___
for O5-C2-C1: angle=117.1 deg___ for O6-C2-C1: angle=117.1 deg___

## Bond Orders (Mulliken):

between C1 and C2: order=0.892___ between C1 and O3: order=1.580___
between C1 and O4: order=1.583___ between C2 and O5: order=1.581___
between C2 and O6: order=1.581___ between O3 and O4: order=-0.192___
between O5 and O6: order=-0.193___

## Best Lewis Structure

The Lewis structure that is closest to your structure is determined. The hybridization of the atoms in this idealized Lewis structure is given in the table below. Please note that your structure can't be well described by a single Lewis structure, because of extensive delocalization.

### Hybridization in the Best Lewis Structure

1. A bonding orbital for C1-C2 with 1.9831 electrons
__has 50.00% C 1 character in a sp2.24 hybrid
__has 50.00% C 2 character in a sp2.24 hybrid

2. A bonding orbital for C1-O3 with 1.9961 electrons
__has 17.71% C 1 character in a p3 hybrid
__has 82.29% O 3 character in a p3 hybrid

3. A bonding orbital for C1-O3 with 1.9950 electrons
__has 35.61% C 1 character in a sp1.85 hybrid
__has 64.39% O 3 character in a sp1.91 hybrid

4. A bonding orbital for C1-O4 with 1.9952 electrons
__has 35.62% C 1 character in a sp1.85 hybrid
__has 64.38% O 4 character in a sp1.92 hybrid

5. A bonding orbital for C2-O5 with 1.9959 electrons
__has 17.80% C 2 character in a p3 hybrid
__has 82.20% O 5 character in a p3 hybrid

6. A bonding orbital for C2-O5 with 1.9946 electrons
__has 35.54% C 2 character in a sp1.87 hybrid
__has 64.46% O 5 character in a sp1.92 hybrid

7. A bonding orbital for C2-O6 with 1.9954 electrons
__has 35.66% C 2 character in a sp1.85 hybrid
__has 64.34% O 6 character in a sp1.90 hybrid

14. A lone pair orbital for O3 with 1.9817 electrons

15. A lone pair orbital for O3 with 1.9195 electrons

16. A lone pair orbital for O4 with 1.9818 electrons

17. A lone pair orbital for O4 with 1.9195 electrons

18. A lone pair orbital for O4 with 1.6956 electrons

19. A lone pair orbital for O5 with 1.9817 electrons

20. A lone pair orbital for O5 with 1.9195 electrons

21. A lone pair orbital for O6 with 1.9817 electrons

22. A lone pair orbital for O6 with 1.9195 electrons

23. A lone pair orbital for O6 with 1.6971 electrons

138. A antibonding orbital for C1-C2 with 0.1308 electrons
__has 50.00% C 1 character in a sp2.24 hybrid
__has 50.00% C 2 character in a sp2.24 hybrid

139. A antibonding orbital for C1-O3 with 0.3025 electrons
__has 82.29% C 1 character in a p3 hybrid
__has 17.71% O 3 character in a p3 hybrid

142. A antibonding orbital for C2-O5 with 0.3017 electrons
__has 82.20% C 2 character in a p3 hybrid
__has 17.80% O 5 character in a p3 hybrid

-With core pairs on: C 1 C 2 O 3 O 4 O 5 O 6 -

#### Donor Acceptor Interactions in the Best Lewis Structure

The localized orbitals in your best Lewis structure can interact strongly. A filled bonding or lone pair orbital can act as a donor and an empty or filled bonding, antibonding, or lone pair orbital can act as an acceptor. These interactions can strengthen and weaken bonds. For example, a lone pair donor->antibonding acceptor orbital interaction will weaken the bond associated with the antibonding orbital. Conversly, an interaction with a bonding pair as the acceptor will strengthen the bond. Strong electron delocalization in your best Lewis structure will also show up as donor-acceptor interactions.
Interactions greater than 20 kJ/mol for bonding and lone pair orbitals are listed below.

The interaction of the second lone pair donor orbital, 15, for O3 with the antibonding acceptor orbital, 138, for C1-C2 is 87.0 kJ/mol.

The interaction of the second lone pair donor orbital, 15, for O3 with the antibonding acceptor orbital, 141, for C1-O4 is 96.8 kJ/mol.

The interaction of the second lone pair donor orbital, 17, for O4 with the antibonding acceptor orbital, 138, for C1-C2 is 86.6 kJ/mol.

The interaction of the second lone pair donor orbital, 17, for O4 with the second antibonding acceptor orbital, 140, for C1-O3 is 96.4 kJ/mol.

The interaction of the third lone pair donor orbital, 18, for O4 with the antibonding acceptor orbital, 139, for C1-O3 is 606. kJ/mol.

The interaction of the second lone pair donor orbital, 20, for O5 with the antibonding acceptor orbital, 138, for C1-C2 is 86.9 kJ/mol.

The interaction of the second lone pair donor orbital, 20, for O5 with the antibonding acceptor orbital, 144, for C2-O6 is 96.7 kJ/mol.

The interaction of the second lone pair donor orbital, 22, for O6 with the antibonding acceptor orbital, 138, for C1-C2 is 86.9 kJ/mol.

The interaction of the second lone pair donor orbital, 22, for O6 with the second antibonding acceptor orbital, 143, for C2-O5 is 96.4 kJ/mol.

The interaction of the third lone pair donor orbital, 23, for O6 with the antibonding acceptor orbital, 142, for C2-O5 is 599. kJ/mol.

## Molecular Orbital Energies

The orbital energies are given in eV, where 1 eV=96.49 kJ/mol. Orbitals with very low energy are core 1s orbitals. More antibonding orbitals than you might expect are sometimes listed, because d orbitals are always included for heavy atoms and p orbitals are included for H atoms. Up spins are shown with a ^ and down spins are shown as v.

27 ----- 13.17
26 ----- 12.41

25 ----- 9.977 24 ----- 9.925

23 -^-v- 5.184

22 -^-v- 4.534 21 -^-v- 4.519

20 -^-v- 3.961
19 -^-v- 3.654

18 -^-v- 2.866

17 -^-v- 0.835
16 -^-v- 0.821

15 -^-v- -0.159 14 -^-v- -0.161

13 -^-v- -0.544

12 -^-v- -1.217

11 -^-v- -4.451

10 -^-v- -12.88 9 -^-v- -12.89

8 -^-v- -14.71

7 -^-v- -15.44

6 -^-v- -258.5 5 -^-v- -258.5

4 -^-v- -495.1 3 -^-v- -495.1 2 -^-v- -495.1 1 -^-v- -495.1

## Total Electronic Energy

The total electronic energy is a very large number, so by convention the units are given in atomic units, that is Hartrees (H). One Hartree is 2625.5 kJ/mol. The energy reference is for totally dissociated atoms. In other words, the reference state is a gas consisting of nuclei and electrons all at infinite distance from each other. The electronic energy includes all electric interactions and the kinetic energy of the electrons. This energy does not include translation, rotation, or vibration of the the molecule.

Total electronic energy = -377.2431559894 Hartrees

* Note: see Robert E. Dinnebier, Sascha Vensky, Martin Pantho1fer, and Martin Jansen, "Crystal and Molecular Structures of Alkali Oxalates: First Proof of a Staggered Oxalate Anion in the Solid State," Inorg. Chem. 2003, 42, 1499-1507.