SARAH COURTNEY SUTTON: An Integrative Synthetic, Spectroscopic and Computational Study of the Free Radical Chlorine Dioxide and Its Interactions with. The existing literature shows inconsistencies in the explanation of the solvent-dependent properties of ClO2. Chlorine dioxide (ClO2) has received considerable attention for its ability to purify drinking water without creating harmful concentrations of disinfection byproducts,1,2 its strong antimicrobial properties,3 and its ability to oxidize atmospheric ozone.4 The unique oxidation properties of ClO2 are believed to be a result of the highly selective nature of an electron-transfer reaction. ClO2 is a neutral free radical with C2v. symmetry and its total dipole moment is 1.792 Debye.5.
Lewis developed a technique to derive molecular bonds based on the valence electrons of the participating atoms.
Symmetry
An active IR or Raman vibration frequency shifts to a lower frequency when hydrogen bonds are formed. A single prime number (Cn̍) indicates that the axis passes through different atoms of the molecule, while a double prime number (Cn̎) indicates that the axis passes through the bonds between atoms. If the atoms of a molecule can be exchanged across the axis of a mirror plane and remain the same, the molecule contains a reflection element.
In 1,2-dibromoethane, shown in Figure 2c, Br1 and Br2 can be exchanged without changing the configuration of the molecule.
Point Groups
A rotation-reflection operation, or improper rotation, involves a rotation followed by a reflection across the axis perpendicular to the axis of rotation. When CH4 is rotated 90 ̊ about its C4 axis and reflected across the plane perpendicular to the axis, its configuration remains the same.
Group Theory
The labels A, B, E and T are used to indicate the symmetry and dimension of the irreducible representation. The label E indicates that the representation is doubly degenerate, or two-dimensional, and the label T indicates that the representation is triply degenerate, or three-dimensional. The subscripts 1 and 2 specify whether the representation is symmetric or antisymmetric, respectively, with the C2 rotation perpendicular to the main rotation axis.
The index g (gerade) and v (ungerade) determine whether the irreducible representation is symmetric or antisymmetric with respect to the inversion.
Molecular Orbital Theory
The molecular orbital (MO) diagram for a homonuclear diatomic molecule consisting of s orbitals of atoms a and b is shown in Figure 1.5. A molecular orbital diagram of the p orbitals of a homonuclear diatom is shown in Figure 1.7. a) pz orbitals (b) px orbitals (c) py orbitals. When all three atomic orbitals have the same symmetry and all their frontiers are in phase, a bonding molecular orbital is formed.
When all three atomic orbitals have the same symmetry but their lobes are out of phase, an antibonding molecular orbital is formed.
Spectroscopic Methods
- Fundamentals of Spectroscopy
- Vibrational Spectroscopy
- Raman Spectroscopy
- UV-Vis Spectroscopy
- Comparing the Raman and UV-Vis Spectra of Chlorine Dioxide
Force is also equal to the negative change in potential energy (V) when an object changes position. Elastic scattering, known as Rayleigh scattering, occurs when the energy of the scattered light equals the energy of the incident light. Inelastic scattering occurs when the energy of the scattered light is not equal to the energy of the incident light.
The dipole moment is proportional to the magnitude of the electric field, depending on its polarizability.
Computational Chemistry
Fundamentals of Computational Chemistry
-Vis absorption spectroscopy and Raman spectroscopy study different energy transitions. a) UV-Vis absorption spectroscopy studies electronic transitions. Within each electronic transition are vibrational transitions corresponding to the peaks in Figure 1.11. Equilibrium geometries are characterized by a positive second derivative of the PES, while transition states are characterized by a negative second derivative of the PES.
To determine whether a given coordinate corresponds to an energy minimum, the original set of coordinates must be replaced by a new set of coordinates (i). Stationary points where the second derivative of the potential energy with respect to normal coordinates is positive are energy minima (equation 1.23).
Hartree-Fock Orbital Theory
The equation for the Hamiltonian (𝐻̂) determines the kinetic and potential energy for each electron, as shown in Equation 1.25. ZA is the nuclear charge of atom A, MA is the mass of the nucleus of A, me is the mass of the electron, RAB is the distance between A and B, rij is the distance between electrons i and j, riA is the distance between the two electrons. I and core A, 0. This gives the electronic Schrodinger equation in Equation 1.26, where the equation for the Hamiltonian is shown below.
The existence of only two spin functions leads to the assumption that two electrons can occupy a molecular orbital. An additional approximation can also be added to transform the Hartree-Fock equations into algebraic equations. This approximation assumes that the one-electron solutions for a many-electron system resemble the one-electron wavefunctions for the hydrogen atom.
Molecular orbitals are then described as linear combinations of a basis set of functions known as basis functions ( shown in equation 1.28, where ci are the molecular orbital coefficients.9.
Density Functional Theory
2 Introducing Students to a Synthetic and Spectroscopic Study of the Free Radical Chlorine Dioxide
- Introduction
- Experimental Methods .1 Synthetic Methods
- Computational Methods
- Hazards
- Results and Discussion
- Conclusions
The broad band at 350 nm in the absorption spectrum of aqueous ClO2 is the result of a transition from the X 2B1 ground state to the A 2A2 excited state. For diatomic molecules, ν̃𝑒′, the fundamental vibrational frequency, can be extrapolated from the absorption spectrum by constructing a Birge-Sponer plot.26 The difference, in wavenumbers, between the discrete vibrational peaks in the UV-Vis spectrum (Δ𝜈̃(v )) is plotted versus the corresponding vibrational energy level (v'). This commonality can be reinforced by the optional computational chemistry component of the exercise.
During this time, students can continue with the computational chemistry elective component of the tutorial. A small portion of the ClO2 aqueous solution in the Schlenk flask was extracted with diethyl ether. The absorption spectrum of the first excited state was simulated using the CIS method and the same basis set.
The first excited state frequencies were also calculated with the CIS method and the same basis. If the computational component is completed, students should also have a simulated UV-Vis spectrum, ground and excited state vibrational frequencies, and NBO analysis results. For students completing the optional computational component of the lab, the differences between the experimental and simulated spectra should be noted.
The maximum absorption of the simulated excited-state UV-Vis spectrum (475 nm) should also be relatively close to the maximum absorption of the experimental UV-Vis spectrum (350 nm). Every student in the 2016 lab successfully obtained a UV-Vis and Raman spectrum and completed the computational component.
- Introduction
- Experimental Methods
- Results and Discussion
- Conclusions
Water was chosen as the solvent due to the widespread use of ClO2 in water purification systems. Geometry optimization and Raman frequency calculations of ClO2/(H2O)x(x=1-3) in the ground state were performed using the unrestricted B3LYP method and split valence basis sets 6- 31+G(d,p ) and 6- 311++G(2df,2dp). Aguilar previously used the B3LYP method with the 6-31+G(d,p) basis set to calculate the optimized geometries of ClO2 and various aniline compounds.58 This study also focuses on changes in the fundamental symmetric stretching mode (1 ). is located at ∼945 cm-1, due to increased soln.
This mode was chosen because 1 can be observed experimentally and has been examined in previous studies.4,11 The calculated Raman shifts for 1 were then compared with the experimental Raman shifts of ClO2 solutions at various concentrations. These were compared to spectra of ClO2 in water to determine solvent effects on hydrogen bond formation. The 1wa and 1wb structures appear to be the same structure, but the position of H2O relative to the xz plane of ClO2 is different.
The simulated spectrum for the 6-31G(d,p) method does not show any correlation between the solvation of ClO2 and water. The spectrum of the single ClO2 molecule is also a) Experimental Raman spectrum of ClO2 in water at increasing concentration. a) Experimental Raman spectrum of ClO2 in methanol. Experimental Raman spectra of ClO2 in water (blue) and methanol (red) give different Raman shifts for its symmetric stretching mode (1).
The simulated Raman spectra of ClO2 in water (blue) and methanol (red) yield different Raman shifts due to the symmetric stretching mode (1). Overall, the total relative energy of ClO2 decreased as the number of interactions between ClO2 and water increased.
4 References
A 2A2 ← X 2B1 Absorption and Raman Spectra of the OClO Molecule: A Three-Dimensional Time-Dependent Wavepacket Study. The Electronic Absorption Spectrum of Molecular Iodine: A New Adaptation Procedure for the Physicochemical Laboratory. The electronic absorption spectrum of molecular iodine: a new fitting procedure for the physicochemical laboratory.
Absorption 2A 2←X 2B 1 and Raman spectrum of the OClO molecule: a three-dimensional time-dependent wavepacket study. Absorption and resonance Raman study of the gas phase transition of 2B1(X)−2A2(A) chlorine dioxide. Theoretical investigation of the excited states of the OClO radical, cation and anion using the CASSCF/CASPT2 method.
The role of spore coat layers in the resistance of Bacillus subtilis spores to hydrogen peroxide, artificial UV-C, UV-B and solar UV radiation. Persistence of pharmaceuticals and other organic compounds in chlorinated drinking water as a function of time. Occurrence, genotoxicity and carcinogenicity of regulated and emerging disinfection byproducts in drinking water: A review and guidelines for research.
Resonance Raman intensity analysis of chlorine dioxide dissolved in chloroform: The role of nonpolar solvation. Kinetics and mechanism for the oxidation of anilines by ClO2: a combined experimental and computational study.
APPENDIX
This laboratory focuses on both the synthesis and spectroscopic analysis of the free radical chlorine dioxide (ClO2). Beer's law shows that each molecule has a characteristic absorbance depending on the extinction coefficient and the concentration of the sample. The type of excitation that occurs during absorption spectroscopy depends on the wavelength range of the incident light.
If the energy of the incident photon is equal to the energy of a rotational, vibrational or electronic transition, the light will be absorbed. A design similar to that in Figure 5 should be constructed by the students at the beginning of the laboratory exercise. A stir bar may need to be used to dissolve all the sodium chlorite.
After ensuring that the addition funnel stop valve is properly closed, this solution is added to the 100 ml addition funnel, being careful not to add the stir bar. Make sure the glass tube entering the top of the flask and the outgoing side arm are greased. Seal the top of the flask with parafilm and wrap the body of the flask in aluminum foil.
Calculate the difference between the vibrational peaks (in wavenumbers) in the absorption spectrum of as many peaks as you can and compare these values with the value of the symmetric stretching mode in the Raman spectrum. A design similar to that in Figure 1 should be constructed by the students at the beginning of the laboratory exercise.
