Electron Spin Resonance Spectroscopy Dylan W. Benningfield Department of Chemistry

Electron Spin Resonance (ESR) Electron paramagnetic resonance (EPR) Study of paramagnetic materials Radicals, bi-radicals, triplet states, unfilled conduction bands, transition metal ions, impurities in semi-conductors, etc. Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Electron Spin Resonance (ESR) Provides molecular structure information inaccessible by other analytical methods Stable paramagnetic species are more easily detected Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Overview Molecules with one or more unpaired electrons Unpaired electrons have spin and charge (magnetic moment) Electronic spin can be in one of two directions Electron spin states are initially degenerate Degeneracy lost when exposed to external magnetic field Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Overview Place sample into magnetic field (B) Irradiate sample with microwave frequencies (GHz) Scan B at constant frequency to make spectra Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html http://en.wikipedia.org/wiki/File:EPR_lines.png http://photonicswiki.org

ESR Overview Microwave source and detector Modulation of magnetic field and phase-sensitive detection Spectrum of 1st derivative (shown below) Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Theory g-value (𝑔) ≈ chemical shift 𝑔 𝑒 = 2.00232 for a free electron Generally 𝑔 = 1.8-2.2 “Resonance” occurs when microwave frequency (GHz) = ∆E Electron spin resonance (ESR), or electron paramagnetic resonance (EPR) is a technique used to study unpaired electrons in a molecular system. Generally used to study radicals and coordination complexes. Unpaired electrons will interact with their chemical environment which produces unique spectra for different compounds http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Energy Levels ∆𝐸= 𝐸 + − 𝐸 − =ℎ𝑣=𝑔 𝜇 𝐵 𝐵 𝑔= ℎ𝑣 𝜇 𝐵 𝐵 =71.4484 𝑣(𝐺𝐻𝑧) 𝐵(𝑚𝑇) g is the g-value 𝜇 𝐵 is the Bohr magneton (9.274 x 10 −28 J/G) B is the magnetic field strength (G = 1x 10 −1 mT) http://en.wikipedia.org/wiki/Electron_paramagnetic_resonance http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

Absorption http://en.wikipedia.org/wiki/Stimulated_emission#/media/File:Stimulated_Emission.svg

Microwaves and Waveguides Energy in the microwave region Microwaves handled with a waveguide Several types of waveguides The energy level required for electron transitions is in the microwave region. Microwaves are usually handled with a waveguide which are constructed on the order of size of the microwaves they are transporting. There are several types of waveguides that are used, but X-band are the most common with a size for 3.0-3.3 cm. Free electron resonances is found around 3390 G Using an X-band waveguide. http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

X-band Waveguide X-band waveguides most common Size = 3.0-3.3 cm Free electron resonance ≈ 3390 G The energy level required for electron transitions is in the microwave region. Microwaves are usually handled with a waveguide which are constructed on the order of size of the microwaves they are transporting. There are several types of waveguides that are used, but X-band are the most common with a size for 3.0-3.3 cm. Free electron resonances is found around 3390 G Using an X-band waveguide. http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Alternative Waveguide Fun fact: the waveguide letters are randomized, b/c in WW2 they were used as code to denote which radio freq they were using to try to detect incoming bombers. The first observation of epr resonance was done with S-band. http://en.wikipedia.org/wiki/Electron_paramagnetic_resonance

𝑁 + 𝑁 − = 𝑒 − ∆𝐸 𝑘 𝐵 𝑇 = 𝑒 − ℎ𝑣 𝑘 𝐵 𝑇 = 𝑒 − 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 Sensitivity ESR focuses on absorption of photons by the sample Net Absorption ( 𝑁 − − 𝑁 + ) can be found using the Boltzmann distribution seen below: 𝑁 + 𝑁 − = 𝑒 − ∆𝐸 𝑘 𝐵 𝑇 = 𝑒 − ℎ𝑣 𝑘 𝐵 𝑇 = 𝑒 − 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

𝑁 − − 𝑁 + = 𝑁 − 1− 1− 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 = 𝑁𝑔 𝜇 𝐵 𝐵 2 𝑘 𝐵 𝑇 Sensitivity For most commonly used temperatures and magnetic fields, the exponent is very small and can be approximated as the following: 𝑒 − 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 ≈1− 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 This allows for the following simplification for 𝑁 − − 𝑁 + : 𝑁 − − 𝑁 + = 𝑁 − 1− 1− 𝑔 𝜇 𝐵 𝐵 𝑘 𝐵 𝑇 = 𝑁𝑔 𝜇 𝐵 𝐵 2 𝑘 𝐵 𝑇 http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

𝑁 − − 𝑁 + = 𝑁 − 1− 1− 𝑔 𝜇 𝑔 𝐵 𝑘 𝐵 𝑇 = 𝑁𝑔 𝜇 𝐵 𝐵 2 𝑘 𝐵 𝑇 Sensitivity 𝑁 − − 𝑁 + = 𝑁 − 1− 1− 𝑔 𝜇 𝑔 𝐵 𝑘 𝐵 𝑇 = 𝑁𝑔 𝜇 𝐵 𝐵 2 𝑘 𝐵 𝑇 This equations shows that ESR sensitivity (net absorption) increases with magnetic field strength and decreasing temperature http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Saturation Spin-lattice Relaxation Instead of simply raising in energy and then releasing it, the excited state becomes “full” at which point the intensity of absorption is lessened. This is related to relaxation times. Molecules with short relaxation times will not become saturated as easily. This is the reason that it is better to use certain frequencies for different samples. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Saturation Instrument must be temperature controlled Instead of simply raising in energy and then releasing it, the excited state becomes “full” at which point the intensity of absorption is lessened. This is related to relaxation times. Molecules with short relaxation times will not become saturated as easily. This is the reason that it is better to use certain frequencies for different samples. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

ESR Instrumentation An ESR Spectrometer have 6 main parts: Klystron Tube (microwave generator) Attenuator Circulator Load Sample Cavity Diode Detector with μ-Ammeter http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Klystron Tube Reflector electrode Anode Electron pathway Heated Filament Cathode The anode distance is a coarse adjustment and changing the voltage is the fine adjustment for the wavelength of the microwaves produced http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Klystron Tube λ of the microwave = sample cavity size. Anode = coarse correction for the λ of the microwave. Voltage = fine correction for the λ of the microwave When preparing a Klystron tube, the λ of the microwave needs to equal the sample cavity size. The anode plate of the Klystron tube can be moved as a coarse correction for the λ of the microwave. The voltage ran through the tube is used as the fine correction for the λ of the microwave http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Attenuator The attenuator homogenizes the power of the incoming microwaves Does not change frequency Reduces noise http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Circulator The circulator is used to direct the microwaves Keeps microwaves from reflecting back towards the source http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Load Completely absorb any reflected microwaves Turns microwaves to heat energy http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Sample Cavity An oscillating magnetic field is super-imposed on the d.c. Adds a.c. component in the diode current An oscillating magnetic field is super-imposed on the d.c. field by means of small coils, usually built into the sample cavity walls. When the field is in the vicinity of a resonance line, it is swept back and forth through part of the line, leading to an a.c. component in the diode current http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

ESR Instrumentation www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

𝒗 Resonance 𝑄= (𝑣 𝑟𝑒𝑠 )/(∆𝑣) An oscillating magnetic field is super-imposed on the d.c. field by means of small coils, usually built into the sample cavity walls. When the field is in the vicinity of a resonance line, it is swept back and forth through part of the line, leading to an a.c. component in the diode current 𝑄= (𝑣 𝑟𝑒𝑠 )/(∆𝑣) www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

ESR Instrumentation Kystron tube will generate microwaves. The Attenuator adjusts the power of the microwaves to the desired level. The circulator routes the microwaves into the correct path so that they go toward the cavity. The microwaves being reflected from the cavity (less power if sample absorbs) will be sent to the diode detector. Any microwave reflect from the detector will be fully absorbed by the load. www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

Diode Detector and μ-Ammeter Current is proportional to microwave power reflected from the sample cavity Plain d.c. measurements have too much noise a.c. component is added in the sample cavity The diode detector is mounted along the E-vector of the plane-polarized microwaves. This produces a current that is proportional to the microwave power reflected from the sample cavity. However, the plain d.c. measurement has too much noise to be useful on its own. In order to compensate for this, there is an a.c. component is added with the modification of the sample cavity http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

ESR Instrumentation www.auburn.edu/~duinedu/epr/2_pracaspects.pdf

ESR Spectra This a.c. component is amplified using a frequency selective amplifier Modulation amplitude is less than the line width Detected a.c. signal is proportional to the change in sample absorption This a.c. component is amplified using a frequency selective amplifier, thus eliminating a great deal of noise. The modulation amplitude is normally less than the line width. Thus the detected a.c. signal is proportional to the change in sample absorption. http://en.wikipedia.org/wiki/Electron_paramagnetic_resonance#/media/File:EPR_lines.png

ESR Spectra Absorbance = Too Noisy 1st derivative = better apparent resolution 2nd derivative = even better resolution, but less sensitive The spectrum can also be shown using the 2nd derivative. But the more time the data is differentiated, the lower the sensitivity. Only 1st and 2nd derivative plots are commonly used to analyze the spectra http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Coalescence Similar to NMR, ESR signals can coalesce at higher temperatures Some compounds have to be run at lower temperatures (or higher field strength) in order to see all of the necessary details in the chromatogram http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Nuclear Hyperfine Interactions Hyperfine coupling is caused by the interaction between the magnetic moments arising from the spins of both the nucleus and electrons in atoms. As shown in Figure 1, in a single electron system the electron with its own magnetic moment moves within the magnetic dipole field of the nucleus. B is magnetic field, μ is dipole moment, ‘N’ refers to the nucleus, ‘e’ refers to the electron: http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Hyperfine Coupling Constant http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Nuclear Hyperfine Interactions http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Nuclear Hyperfine Interactions It is important to note that the spacing between peaks is 'a', the hyperfine coupling constant. This constant is equivalent for both protons in the equivalent system but unequal for the unequivalent protons. http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Nuclear Hyperfine Interactions 𝐵 1 = ℎ𝑣− 𝑎 2 𝑔 𝜇 𝐵 𝐵 2 = ℎ𝑣+ 𝑎 2 𝑔 𝜇 𝐵 B = field strength a = hyperfine coupling constant g = g-value ℎ𝑣 = frequency of radiation 𝜇 𝐵 = Bohr magneton http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Nuclear Hyperfine Interactions ∆𝐵= 𝐵 2 − 𝐵 1 = ℎ𝑣+ 𝑎 2 𝑔 𝜇 𝐵 − ℎ𝑣− 𝑎 2 𝑔 𝜇 𝐵 𝑎= 𝑔 𝜇 𝐵 ∆𝐵 B = field strength a = hyperfine coupling constant g = g-value ℎ𝑣 = frequency of radiation 𝜇 𝐵 = Bohr magneton http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Superhyperfine Splitting Further splitting from hyperfine interactions Very small Due to neighboring nuclei http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Isotropic and Anisotropic Interactions Electron-nuclei interactions have several mechanisms, the most prevalent being Fermi contact interaction and dipole interaction. Dipole interactions occur between the magnetic moments of the nucleus and electron as an electron moves around a nucleus. However, as an electron approaches a nucleus, it has a magnetic moment associated with it. As this magnetic moment moves very close to the nucleus, the magnetic field associated with that nucleus is no longer entirely dipolar. The resulting interaction of these magnetic moments while the electron and nucleus are in contact is radically different from the dipolar interaction of the electron when it is outside the nucleus. This non-dipolar interaction of a nucleus and electron spin in contact is the Fermi contact interaction. A comparison of this is shown in Figure 6. The sum of these interactions is the overall hyperfine coupling of the system. Fermi contact interactions predominate with isotropic interactions, meaning sample orientation to the magnetic field does not affect the interaction. Due to the fact that this interaction only occurs when the electron is inside the nucleus, only electrons in the s orbital exhibit this kind of interaction. All other orbitals (p,d,f) contain a node at the nucleus and can never have an electron at that node. The hyperfine coupling constant in isotropic interactions is denoted 'a'. http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Number of Peaks For equivalent nuclei: # 𝑝𝑒𝑎𝑘𝑠=2𝑀𝐼+1 M = number of equivalent nuclei I = nuclear spin number http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Number of Peaks For more than one set of equivalent nuclei: # 𝑝𝑒𝑎𝑘𝑠= 2 𝑀 1 𝐼 1 +1 2 𝑀 2 𝐼 2 +1 2 𝑀 3 𝐼 3 +1 … M = number of equivalent nuclei I = nuclear spin number http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Number of Peaks http://www.auburn.edu/~duinedu/epr/3%20theory.pdf

Common Nuclear Spins http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

Common Nuclear Spins http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

Number of Peaks Example: radical CO2 # 𝑝𝑒𝑎𝑘𝑠=2𝑀𝐼+1 2 Oxygen, I = 3 2 # 𝑝𝑒𝑎𝑘𝑠=2𝑀𝐼+1 #𝑝𝑒𝑎𝑘𝑠=(2)(2) 3 2 +1=7 peaks

Number of Peaks Example: radical NH3 1 Nitrogen, I = 1 3 Hydrogen, I = 1 2 # 𝑝𝑒𝑎𝑘𝑠=(2 𝑀 𝑁 𝐼 𝑁 +1)(2 𝑀 𝐻 𝐼 𝐻 +1) #𝑝𝑒𝑎𝑘𝑠=( 2 1 1 +1)((2)(3) 1 2 +1)=12 peaks

Practice ESR Spectra Oxygen has an I = 3 2 For compounds with equivalent nuclei, #peaks=2𝑀𝐼+1 #𝑝𝑒𝑎𝑘𝑠=(2)(2) 3 2 +1=7 •+

Practice ESR Spectra •+ Oxygen radical SDBSWeb : http://sdbs.db.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 3/24/2015)

Practice ESR Spectra 3 H, I = 1 2 1 C, I = 0 For compounds with equivalent nuclei, #peaks=2𝑀𝐼+1 #𝑝𝑒𝑎𝑘𝑠=(2)(3) 1 2 +1=4

Practice ESR Spectra Methyl radical http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

Practice ESR Spectra 2 H with I = 1 2 1 N with I = 1 (2)(2) 1 2 +1 = 3 peaks 1 N with I = 1 (1)(2) 1 2 +1 = 3 peaks For multiple sets of nuclei: # 𝑝𝑒𝑎𝑘𝑠= 2 𝑀 1 𝐼 1 +1 2 𝑀 2 𝐼 2 +1 2 𝑀 3 𝐼 3 +1 … Thus, there are (3)(3) = 9 total peaks

Practice ESR Spectra Acetonitrile radical Superhyperfine splitting occurs to make a triplet of triplets. The electron is closer to the hydrogens most of the time, so that the N provides the triplet of triplet superhyperfine splitting effect. Acetonitrile radical SDBSWeb : http://sdbs.db.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 3/24/2015)

Practice ESR Spectra 8 H, 2 sets of 4 equivalent nuclei (4)(2) 1 2 +1 = 5 peaks Thus, there are (5)(5) = 25 total peaks •-

Practice ESR Spectra •- Naphthalene radical anion SDBSWeb : http://sdbs.db.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 3/24/2015)

Practice ESR Spectra (a) Isotropic ESR spectrum of (Ph2C2)Co(CO)2P(OMe)3(1) in THF solution at 260 K (from reference 12); (b) Second-order "stick spectrum"; (c) First-order "stick spectrum". http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Practice ESR Spectra (a) ESR spectrum of 5 in a CH2Cl2/THF glass (49); (b) Computer simulation http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Practice ESR Spectra ESR spectrum of (Ph2C2)Co(CO)[P(OMe)3]2 (a) Experimental spectrum of THF solution at 290 K; (b and c) Computer-simulated spectra including (b) the mCoand mP linewidth dependence, and (c) the mCo linewidth dependence only. http://www.chm.bris.ac.uk/emr/Phil/Phil_2/p_2.html

Practice Problems How many ESR peaks would a compound containing one Cu2+ (I=3/2), one N (I=1), and one –OH (I=1/2) have? http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Practice Problems How many ESR peaks would a compound containing one Cu2+ (I=3/2), one N (I=1), and one –OH (I=1/2) have? ((2*1*3/2+1)(2*1*1+1)(2*1*1/2+1) = 24 peaks http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Practice Problems How many peaks would a methoxymethyl radical have, and how would those peaks appear in the spectra (doublets, triplets, etc.)? http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Practice Problems How many peaks would a methoxymethyl radical have, and how would those peaks appear in the spectra (doublets, triplets, etc.)? 3 H and 2 H (2+1)(3+1)=12 peaks Triplet of quartets http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Practice Problems http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/Hyperfine_Splitting

Practice Problems What is the g-value corresponding to a resonance at 9000 MHz and 3700 G? 𝑔= ℎ𝑣 𝜇 𝐵 𝐵 =71.4484 𝑣(𝐺𝐻𝑧) 𝐵(𝑚𝑇) 1G = 0.1mT

Practice Problems What is the g-value corresponding to a resonance at 9000 MHz and 3700 G? 𝑔= ℎ𝑣 𝜇 𝐵 𝐵 =71.4484 9(𝐺𝐻𝑧) 370(𝑚𝑇) =1.738

Questions?