In a redox reaction, the oxidant has a low LUMO, and the reductant has a high HOMO, but this time the oxidant LUMO is lower than the reductant HOMO, so that the electrons in the reductant HOMO move completely to the oxidant LUMO. This creates a bond between the acid and base. A low LUMO usually means an empty valence orbital, like on B or on a cation.) We can make a bonding and anti-bonding combination of the base HOMO and acid LUMO, and that will stabilize the electrons from the base's HOMO, lowering the total energy. (A lone pair in MO theory is an electron pair in a non-bonding MO. What this really means is that the base has a HOMO that is pretty high-energy (a lone pair), and the acid has a LUMO that is pretty low energy. In a Lewis acid/base reaction, an electron pair from the base is shared with the acid. Earlier, we said that most reactions can be called either Lewis acid/base or redox. LUMO is Lowest Unoccupied MO, the lowest-energy MO that doesn't have any electrons in it.įrontier MOs are very important for reactivity. HOMO is Highest Occupied MO, the highest-energy MO that has electrons in it. The frontier MOs are called the HOMO and the LUMO. In this case, we are interested in the MOs at the border between occupied and empty. Distinguish and describe the significance of frontier MOsįrontier means a border area, between two things (often, between 2 countries).Can the sweep rate change the observed redox potential? Yes.\( \newcommand\).Could the oxidized or reduced species undergo reactions that change the observed redox potential? Yes.Could the molecules aggregate and change the observed redox potential? Yes.Can the electrode change the observed redox potential? Yes.Can the solvent change the observed redox potential? Yes.There should be a correlation between oxidation and reduction potentials and HOMO and LUMO energies.īut step back and think - in one case, you have electrochemistry in the electrolyte solution at an electrode surface. When you sweep the potential with CV, the cathodic peak ($E_$$Īre these peaks even the HOMO/LUMO levels at all? Note that the "peak" actually has two sides. Let's start with interpreting the cyclic voltammetry curves themselves. Yes, you can "convert" this way, but you're correct to be skeptical. " Often cyclic-voltammetry-based ionization potentials and electronĪffinities are inappropriately referred to as "HOMO" and "LUMO" What justification do I use to convert the voltage to an energy? How can I say that a difference in mV corresponds to eV? Maybe this might make sense if it was a one electron process, but how do I know that?Īre these peaks even the HOMO/LUMO levels at all? In this eminent paper it warns me It has been explained to me I just need to measure the mV difference between the peak of the ferrocene and the oxidation or reduction curve, then subtract/add that onto the reference for ferrocene (4.8eV) to get the HOMO/LUMO levels.ĭo I measure to the onset of the oxidation/reduction curve or the My CV measurements result in a current-voltage curve (IV curve). I am interested in determining the HOMO and LUMO levels of the material. I've carried out CV measurements on a few different types of material (with a ferrocene reference). I'm a physicist, so I apologize if these are obvious questions.
0 kommentar(er)
