ESR Lab Activity
Introduction
We are going to collect an ESR spectrum from a series of substituted hydroquinones.
| Name | SDS | Molar Mass | Sigma Product Number | Cost |
| A = Hydroquinone (aka. 1,4-benzohydroquinone) | SDS | 110.11 g/mol | H9003 | 22.90 / 100g |
| B = Methylhydroquinone | SDS | 124.14 g/mol | 112968 | 59.20 / 250g |
| C = 2,3-dimethylhydroquinone | SDS | 138.16 g/mol | 300756 | 118.00 / 5g |
Experimental
Beaker Method
- Solution A: 1 M NaOH; 1 gram NaOH (39.997 g/mol) into 25 mL EtOH.
- Solution B: 1 M hydroquinone solution.
- Procedure: To 2 ml of 1 M hydroquinone solution add 2-3 drops of solution A. A color change will indicate the reaction has occurred. Quickly transfer colored sample to ESR sample tube, place in ESR spectrometer, tune, and collected data.
Flow Method
- Solution A: 0.05 M NaOH; 0.05 grams NaOH (39.997 g/mol) into 25 ml EtOH.
- Solution B: 1 M hydroquinone solution.
- Procedure: Prepare two 60 ml syringes, 1 with solution A and 1 with solution B.
- Degas the syringe that contains solution B
- Attach to double syringe drive
- Turn on double syringe drive that is attached to ESR
- Collect data
Double Syringe Drive
Results
1-electron Oxidation of Hydroquinone
This is the EPR spectrum of the "hydro-semiquinone" (aka. 1,4-benzosemiquinone)
EPR Parameters: 9.4 GHz, 3360 G Center field, 15 G sweep width. [Above data needs the x-axis changed over to magnetic field in G]
1-electron Oxidation of Methylhydroquinone
This is the EPR spectrum of the "methyl-hydro-semiquinone" (aka. methyl-semiquinone)
EPR Parameters: 9.4 GHz, 3360 G Center field, 15 G sweep width. [Above data needs the x-axis changed over to magnetic field in G]
Analysis
WinSim
1-electron Oxidation of Hydroquinone
Hydrosemiquinone ESR spectrum (black) vs Winsim spectrum (red)
Gaussian Calculations
| Atom | HF/3-21G | HF/6-31G | HF/6311G+(2p,d) | B3LYP/6-31G | B3LYP/3-21G | B3LYP/6311G+(2p,d) | HF/EPR-ii | B3LYP/EPR-II | |
| 8 | 12.605 | 12.165 | 0.26898 | 1.10213 | 0.85863 | 0.52092 | 10.405 | 0.30942 | |
| 9 | -14.289 | -14.332 | -0.18982 | -2.73487 | -2.67806 | -2.55611 | -12.281 | -2.45135 | |
| 11 | -14.289 | -14.335 | -0.19007 | -4.10834 | -2.68141 | -2.55653 | -12.281 | -2.44583 | |
| 12 | 12.604 | 12.167 | 0.26907 | 1.27101 | 0.85927 | 0.52095 | 10.405 | 0.30859 | |
| 19 | 12.604 | 12.169 | 21.28576 | 1.27509 | 0.85858 | 0.52091 | 10.405 | 0.30943 | |
| 20 | -14.289 | -14.339 | -24.52739 | -4.09995 | -2.67694 | -2.55567 | -12.281 | -2.45143 | |
| 22 | -14.289 | -20.186 | -24.72440 | -2.74025 | -2.68052 | -2.55603 | -12.281 | -2.44580 | |
| 23 | 12.604 | 12.171 | 21.57883 | 1.10424 | -0.58918 | 0.52091 | 10.405 | 0.30858 | |
| 24 | 0.661 | 0.796 | 17.77623 | 3.46774 | -0.22807 | -0.28092 | 0.786 | -0.40397 | |
| 25 | 0.660 | 0.796 | 17.77641 | 3.27784 | -0.22870 | -0.28078 | 0.786 | -0.40384 |