There are several factors that affect the selectivity of a chemical reaction. These factors can be broadly categorized into the following:1. Steric factors: The size and shape of the reactants and their substituents can influence the selectivity of a reaction. Bulky groups can hinder the approach of reactants, leading to a preference for reactions at less sterically hindered sites.2. Electronic factors: The electronic properties of the reactants, such as their charge distribution and the presence of electron-donating or electron-withdrawing groups, can affect the selectivity of a reaction. These factors can influence the stability of transition states and intermediates, as well as the reactivity of the reactants.3. Solvent effects: The solvent can play a significant role in determining the selectivity of a reaction. Polar solvents can stabilize charged intermediates and transition states, while nonpolar solvents can favor reactions that involve nonpolar intermediates.4. Temperature and pressure: The reaction conditions, such as temperature and pressure, can also influence the selectivity of a reaction. Higher temperatures can increase the rate of a reaction, but may also lead to a decrease in selectivity due to the increased likelihood of side reactions.5. Catalysts: The presence of a catalyst can greatly influence the selectivity of a reaction. Catalysts can lower the activation energy for a specific reaction pathway, leading to a preference for that pathway over others.Quantum chemistry can be used to predict and enhance selectivity in organic synthesis by providing detailed information about the electronic structure and energetics of reactants, intermediates, and transition states. This information can be used to:1. Identify the most favorable reaction pathways: Quantum chemical calculations can help identify the most energetically favorable reaction pathways, which can be used to predict the selectivity of a reaction.2. Design new catalysts: By understanding the electronic structure of reactants and transition states, chemists can design new catalysts that selectively stabilize the desired reaction pathway, leading to enhanced selectivity.3. Optimize reaction conditions: Quantum chemistry can provide insights into the effects of solvents, temperature, and pressure on the energetics of a reaction, allowing chemists to optimize these conditions for maximum selectivity.4. Predict the effects of substituents: Quantum chemical calculations can be used to predict the effects of different substituents on the electronic structure and reactivity of reactants, which can help guide the design of new molecules with improved selectivity.Overall, quantum chemistry is a powerful tool for understanding and predicting the selectivity of chemical reactions, and can be used to guide the design of new molecules and reaction conditions for improved selectivity in organic synthesis.