Resonance structures are theoretical constructs used to enhance the understanding of molecular structures, particularly in complex compounds like benzene. They do not exist as distinct entities but serve as valuable tools for approximating electronic wavefunctions. The discussion highlights the importance of resonance structures in stabilizing compounds and compares them to molecular orbital theory and valence bond theory. Key references include the classic text "Quantum Chemistry" by Eyring, Walther, and Kimball, which provides foundational knowledge on these concepts.
PREREQUISITESChemistry students, researchers, and educators seeking to deepen their understanding of molecular structure and resonance theory.
Head count on "valence shell" electrons, and a rough idea of how they contribute to various bonding.Yashbhatt said:some sort of calculation tool?
Bystander said:Head count on "valence shell" electrons, and a rough idea of how they contribute to various bonding.
"Why use them?" As tools to enhance understanding of molecular structure, they are crude. As a chemist, when working with anything more complex than hydrogen atoms or hydrogen like ions, I'm stuck with crude tools.Yashbhatt said:include them
I think of them as states. More number of resonance structures means more number of states in which the compound can exist thus making the compounds more stable. Is it correct to think of it in that way?Bystander said:"Why use them?" As tools to enhance understanding of molecular structure, they are crude. As a chemist, when working with anything more complex than hydrogen atoms or hydrogen like ions, I'm stuck with crude tools.
I wouldn't call it incorrect. If you'll do a little reading on benzene, Dewar benzene resonance structures, aromaticity, and compare the bond energies of three C-C single bonds plus three C=C double bonds to the delocalization energy of a benzene or aromatic ring, you will find that there is a quantitative difference in the stabilization energy when compared to that of the Dewar resonance structures.Yashbhatt said:Is it correct to think of it in that way?
Bystander said:I wouldn't call it incorrect. If you'll do a little reading on benzene, Dewar benzene resonance structures, aromaticity, and compare the bond energies of three C-C single bonds plus three C=C double bonds to the delocalization energy of a benzene or aromatic ring, you will find that there is a quantitative difference in the stabilization energy when compared to that of the Dewar resonance structures.
Bystander said:I wouldn't call it incorrect. If you'll do a little reading on benzene, Dewar benzene resonance structures, aromaticity, and compare the bond energies of three C-C single bonds plus three C=C double bonds to the delocalization energy of a benzene or aromatic ring, you will find that there is a quantitative difference in the stabilization energy when compared to that of the Dewar resonance structures.
DrDu said:There are different ways to expand a multi-electron wavefunction into a basis set. One approach is molecular orbital theory, where the building blocks are Slater determinants made up of single electron molecular orbitals. Another approach is valence bond theory where the molecular wavefunction is constructed from atomic orbitals. There are different ways of doing so and one approach uses a set of paired atomic orbitals wherea complete set of different independent pairing schemes are found from Rumer diagrams which are the mathematical construct corresponding to the different valence structures.
It often turns out that the electronic wavefunction can be approximated very well as a resonance structure, or, in modern terminology, a superposition of only a handful of valence structures. This makes the valence structures a valuable tool though they aren't unique.
The classic text to understand all this is still be book by Eyring, Walther and Kimball, Quantum chemistry.
Good question. The reality is somewhere between all of the resonance structures. For example, benzene's C-C bond length is somewhere between the single and double bond lengths for carbon.Yashbhatt said:I have a question. Are resonance structures something like dynamic equilibrium(i.e. continuously changing states) or are they something which is in between both the states?