Chap. 3 Bronsted lowery acid: proton donorBronsted Lowery Base: proton acceptor- The products from an acid – base reaction are called conjugate base (product of a strong acid) and conjugate acid (product of strong base). - All reactions are accomplished with curly arrows, these arrows represent the flow of electrons. They are exactly what is used in resonance structures however different the arrows show what is called the reaction mechanism. - A quantitative method of predicting electron transfer is by comparing pKa values. - Equilibrium: when there is no longer an observable change in the concentrations of reactants and products. The position of equilibrium is described by the term Keq. - When an acid – base reaction is carried out with dilute aqueous solution, the concentration of water is fairly constant (55.M) and can therefore be removed leaving us with Ka. - The value Ka measures the strength of the acid:- pKa is the measure of acidity: pKa = - log Ka- Qualitative analysis is a way of comparing acidswithout the use of pKa values, it is a focus on electrons and the structure of acids. For that we must look at the conjugate base where electrons are least stable on the conjugate base. - By determining the more stable conjugate base we can identify the stronger acid.- Qualitative analysis includes: Atom size, electronegativity, Resonance, Inductive effects, Hybridization ad solvent effects- Factors affecting the stability of negative charges: a qualitative comparison of acidity requires comparison of the stability of negative charges. 1. Electronegativity: This first factor involves comparing the atoms bearing the negative charge on each conjugate base.- We compare the conjugate bases by looking at where the negative charge is located.- If, for example, the negative charge is located on the carbon for the first Conj. Base and the negative charge is placed on the oxygen on the second Conj. Base, then we must compare electronegativity of the two.- Electronegativity increases as you go left to right and bottom to top as the size of the atom increases from top to bottom.- All in all there are two important trends that must be looked at; size and electronegativity.2. Resonance- Delocalized charges make the structure more stable- A structure with a resonance is more stable than a structure without a resonance structure to follow it. - If there are two or more structure with equal importance to resonance, then the composition of the structure matters. In other words type of atoms the structure holds leading to electronegativity.3. Induction- The withdrawal of electrons- Ex. Trichloroacetic acid vs. acetic acid: in the trichloroacetic acid the chlorine atoms withdraw electron density via induction however in acetic acid there is nothing withdrawing electron density. The net effect of the chlorine atoms is to withdraw electron density away from the negatively charged region of the compound, hence stabilizing the negative charge. Thus trichloroacetic acid is more stable than acetic acid.4. Orbitals/ Hybridization- The region where the negative charge lies (whether it is sp3, sp2, or sp hybridized atom) determines the acidity.- A negative charge on a sp orbital is more stable than the other two since the electron residing in an sp orbital are stabilized by being close to the nucleus.- The stability increases as we go from sp3 to sp.- An electron on a triple bond is more stable than an electron on a double or single bond.Equlibrium and choice of reagents: it is done by comparing conjugate bases without using pKa value.- The two bases here are (A- and B-) and the main question is which one is more stable.- If A- is more stable then the equilibrium will favor the left side and vice versa if B- is more stable.Lewis acids: electron pair acceptor Lewis Base: electron pair donor- Some reagents are considered acid by the bronsted lowery rules and some are not, forexample Boron fluoride is considered a bronsted lowery base as it accepts protons, but by the lewis acid base rules, it serves as an electron pair donor. Hence is it called alewis