Tutor profile: Natalie J.
Subject: Organic Chemistry
Why are secondary amines more basic than primary and tertiary amines?
Secondary amines benefit from both hyperconjugation as well as limited steric hindrance. Tertiary amines have three attached alkyl groups preventing the lone pair on the nitrogen from being readily available to the solution, and therefore, making protonation difficult. Secondary amines, while more statically hindered than primary amines, benefit from hyper conjugation. Hyperconjugation describes the stability benefit of attached alkyl groups donating electron density into nitrogens empty p orbital. This stabilizes the compound increasing its basicity. Because secondary amines benefit from both of these phenomena, they are the most basic of the amines and therefore have the highest pKa.
If an exothermic chemical reaction is heated, which way will the reaction shift?
Exothermic reactions release heat as they move forward while endothermic reactions require an input of heat. To determine the reaction shift, heat can be treated as a product for exothermic reactions and as a reactant for endothermic reactions. Then using Le Chatelier's principle, adding heat to the exothermic reaction would increase the "concentration" of one of the products. Therefore, the reaction would shift towards the left favoring the reactants.
How does altering the pH of a solution contribute to protein solubility?
Protein solubility is largely dependent on the isoelectric point of the protein. The isoelectric point refers to the pH at which the protein is neutral in charge. This neutrality occurs when there is an equal number of positively and negatively charged side chains. The side chains are protonated and deprotonated in accordance with whatever the pH of the solution is. A solution of low pH will protonate basic side chains while a solution of high pH will deprotonate acidic side chains. Adjusting the pH of the solution above or below the isoelectric point will cause either of these scenarios to occur, thereby increasing the ionic character of the protein. A protein with more ionic character is then more readily soluble in solution. We can then minimize protein solubility by bringing the pH of the solution to the isoelectric point of the protein.
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