6.3: Brønsted-Lowry Concept
- Page ID
- 272344
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- The Br??nsted-Lowry acid-base concept focuses on hydrogen ion (\(H^+\)) transfer, extending the acid-base definition beyond aqueous solutions. A Br??nsted acid donates \(H^+\) to a base, while a Br??nsted base accepts it. This model adapts to diverse environments, handling non-water reactions like hydrochloric acid with ammonia. The concept highlights conjugate acid-base pairs, emphasizing a reciprocal strength relationship; stronger acids have weaker conjugate bases and vice versa.
- 6.3.2: Rules of Thumb for thinking about the relationship between Molecular Structure and Brønsted Acidity and Basicity*
- The document discusses factors affecting acid strength in various solvents, focusing on Br??nsted acidity and basicity. These factors include bond strength (weaker bonds to hydrogen result in stronger acids), inductive effects (electron withdrawing groups increase acidity), and electronegativity effects (more stable conjugate bases enhance acidity). Size effects also play a role, as larger atoms can stabilize charge better, leading to stronger acids.
- 6.3.3: The acid-base behavior of binary element hydrides is determined primarily by the element's electronegativity and secondarily by the element-hydrogen bond strength
- Binary hydrides are compounds formed between elements and hydrogen, acting as Br??nsted acids or bases depending on their position in the periodic table. Electronegativity and bond strength influence the acidity, with acidic hydrides more common among nonmetals. Hydrides of electropositive metals like NaH and CaH2 act as bases. Acidity increases across a period due to increased electronegativity and polarization, and down a group due to weaker bonds.
- 6.3.4: Brønsted-Lowry Superacids and the Hammett Acidity Function
- Superacids are able to dissociate completely because when they do so they give an extremely stable anion in which the residual negative charge is distributed among multiple electronegative atoms.
- 6.3.5: Thermodynamics of Solution-Phase Brønsted Acidity and Basicity
- The text discusses the influence of solvation on the behavior of Br??nsted-Lowry acids and bases in aqueous systems, with a focus on thermochemical parameters such as enthalpy and entropy changes for acid dissociation. The major driving force for dissociation is the enthalpy, which is exothermic for most acids, except for certain weak acids where entropy plays a larger role.
- 6.3.6: Thermodynamics of Gas Phase Brønsted Acidity and Basicity
- This page discusses the thermodynamic aspects of hydrogen ion transfer focusing on proton affinity (PA) and gas phase acidity/basicity. Proton affinity is defined as the enthalpy change for the association or dissociation of a hydrogen ion and a base in the gas phase, while gas phase basicity relates to Gibbs free energy change. These values help in understanding acidity trends and the role of solvation in acid-base behavior in different media.
- 6.3.8: High Charge-to-Size Ratio Metal Ions Act as Brønsted Acids in Water
- Aqueous solutions of simple salts of metal ions can also be acidic, even though a metal ion cannot donate a proton directly to water to produce hydronium ions. Instead, a metal ion can act as a Lewis acid and interact with water, a Lewis base, by coordinating to a lone pair of electrons on the oxygen atom to form a hydrated metal ion.
- 6.3.9: The Solvent System Acid Base Concept
- Like the Brønsted-Lowry acid-base concept, the solvent system acid base concept is way to generalize the Arhennius acid-base concept.
- 6.3.10: Acid-Base Chemistry in Amphoteric Solvents and the Solvent Leveling Effect
- The Brønsted-Lowry concept allows for an understanding of hydrogen ion transfer chemistry in amphoteric protic solvents. Amphoteric protic solvents are those which can both accept and receive hydrogen ions. From the viewpoint of the Brønsted-Lowry concept the acid-base chemistry in these solvents is governed by autoionization equilibria analogous to water autoionization.
- 6.3.11: Non-nucleophilic Brønsted-Lowry Superbases
- A variety of strong organic and inorganic bases are available for use in organic synthesis (alkyllithium reagents, diisopropyl amide derivatives, hydrides, and hydroxides). Some of these exhibit poor functional group tolerance owing to their ability to react with electrophilic functional groups. Hence there is considerable interest in the development of bases that can remove hydrogen ions from very weakly acidic organic substrates (i.e. like C-H bonds) without reacting with electrophilic functio