ESR Lab Activity

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Introduction

We are going to collect an ESR spectrum from a series of substituted hydroquinones.

Hydroquinones.png

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.jpg

Double Syringe Drive

Results

1-electron Oxidation of Hydroquinone

14BZQ.jpg


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

EPR MeH2Q.jpg


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 theoretical vs exp.png

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 1.10213 0.85863 0.52092 10.405 0.30942
9 -14.289 -14.332 -2.73487 -2.67806 -2.55611 -12.281 -2.45135
11 -14.289 -14.335 -4.10834 -2.68141 -2.55653 -12.281 -2.44583
12 12.604 12.167 1.27101 0.85927 0.52095 10.405 0.30859
19 12.604 12.169 1.27509 0.85858 0.52091 10.405 0.30943
20 -14.289 -14.339 -4.09995 -2.67694 -2.55567 -12.281 -2.45143
22 -14.289 -20.186 -2.74025 -2.68052 -2.55603 -12.281 -2.44580
23 12.604 12.171 1.10424 -0.58918 0.52091 10.405 0.30858
24 0.661 0.796 3.46774 -0.22807 -0.28092 0.786 -0.40397
25 0.660 0.796 3.27784 -0.22870 -0.28078 0.786 -0.40384

Basis Sets

Conclusions