![]() ![]() There are a number of powerful QM computing tools available to us. Now let’s use FMO theory to rationalize the aforementioned nucleophilic reactions with the dichloropyrimidine (Figure 1). It enables chemists to understand how orbitals interact with one another throughout the course reactions, and to account for chemical reactivity & selectivity observed, etc. Based on FMO theory, an organic reaction is electron transfer from nucleophilic part (HOMO) to the electrophilic part (LUMO) of the reacting system. For organic reaction, we could focus on the use of Frontier Molecular Orbital (FMO) Theory, which emphasizes the analyses with outer orbitals, i.e., Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO). These orbitals have their own energy levels and unique spatial distribution. You will see that it is relatively easy to understand and apply QM in your laboratories.įirst let’s review the basics of Molecular Orbital (MO) Theory, which proposes that when atoms come together to constitute a molecule, their atomic orbitals interact with each other and form new molecular orbitals. In this article, we will discuss how we use LUMO and LUMO Map to analyze nucleophilic aromatic substitution reactions. The question becomes “What could be the best scientific method to rationalize, to learn these chemistry?” In our synthetic organic chemistry laboratories, we found QM to be the most valid and efficient tool for these purposes. Nucleophilic reaction of 2,4-dichloro-5-methylpyrimidine with alkyl lithium or aliphatic amine Why is it not the case? We also observed that when the nucleophile is alkyllithium, a C-6 addition product is observed instead of C-4 displacement of chloride. Intuitively it makes more sense for the substitution to occur faster at C-2, which has two electron withdrawing aromatic nitrogen atoms next to it. We learned that nucleophilic substitution of 2,4-dichloro-5-methylpyrimidine with a nucleophile, such as piperidine, proceeds preferentially at C-4 position (Figure 1). Please join us to unleash the magical power of Quantum Mechanics (QM). Would you prefer to learn and rationalize organic chemistry in a data-driven manner? Would you like to predict organic reaction outcomes accurately? Design synthetic sequences with higher rate of success? ![]()
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