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
8	12.605	12.165		1.10213	0.85863	0.52092	10.405
9	-14.289	-14.332		-2.73487	-2.67806	-2.55611	-12.281
11	-14.289	-14.335		-4.10834	-2.68141	-2.55653	-12.281
12	12.604	12.167		1.27101	0.85927	0.52095	10.405
19	12.604	12.169		1.27509	0.85858	0.52091	10.405
20	-14.289	-14.339		-4.09995	-2.67694	-2.55567	-12.281
22	-14.289	-20.186		-2.74025	-2.68052	-2.55603	-12.281
23	12.604	12.171		1.10424	-0.58918	0.52091	10.405
24	0.661	0.796		3.46774	-0.22807	-0.28092	0.786
25	0.660	0.796		3.27784	-0.22870	-0.28078	0.786

http://www.gaussian.com/g_tech/g_ur/m_basis_sets.htm