F-B +NH3→FB-NH Lewis acid ewis base (electron-pair (electron-pair acceptor donor) The lewis theory by virtue of its broader definition of acids, allows acid-base theory to include all of the brnsted-Lowry reactions agnd as we shall see, a great many others Any electron-deficient atom can act as a Lewis acid. many compounds containing group iiia elements such as aluminium are Lewis acids because group Iiia atoms have only a sextet of electrons in their outer shell. Many other compounds that have atoms with orbitals also act as Lewis acids. For example
+ NH3 Lewis acid (electron-pair acceptor) Lewis base (electron-pair donor) F B F F F B - F F NH3 + The Lewis theory , by virtue of its broader definition of acids, allows acid-base theory to include all of the Brnsted-Lowry reactions aqnd , as we shall see, a great many others. Any electron-deficient atom can act as a Lewis acid. Many compounds containing group IIIA elements such as aluminium are Lewis acids because group IIIA atoms have only a sextet of electrons in their outer shell. Many other compounds that have atoms with orbitals also act as Lewis acids. For example:
R-O-H ZnCl R-O-ZnCI2 Lewis base Lewis acid H (electron-pair (electron-pair donor) acceptor) Br一Br:+FeBr3 Br一Br-FeBr3 Lewis base Lewis acid (electron-pair (electron-pair donor) acceptor) 3.2 THE USE OF CURVED ARROWS IN ILLUSTRATING REACTIONS the direction of electron flow in a reaction. Besides it is a usely ow The curved arrows is commonly used by organic chemists to sh Method for indicating which bonds form and which bonds break
R O H R O+ Lewis acid H (electron-pair acceptor) Lewis base (electron-pair donor) ZnCl 2 ZnCl 2 - + Br Br + FeBr 3 Br Br + FeBr 3 - Lewis base (electron-pair donor) Lewis acid (electron-pair acceptor) 3.2 THE USE OF CURVED ARROWS IN ILLUSTRATING REACTIONS The curved arrows is commonly used by organic chemists to show the direction of electron flow in a reaction. Besides it is a useful Method for indicating which bonds form and which bonds break
Now. lets us illustrate some of the basic ideas of the curved-arrow notation with simple lewis acid-base reactions H-O?+ H-Cl H—O-H+:Cl H H this bond breaks this bond is formed The following acid-base reactions gives other examples of the use of the curved -arrow notation H-。H+0-H--2H-0 H H Acid B ase
Now, lets us illustrate some of the basic ideas of the curved-arrow notation with simple Lewis acid-base reactions: H O H H Cl H O + H H Cl + - + this bond breaks this bond is formed The following acid-base reactions gives other examples of the use of the curved-arrow notation: H O + H H + O H - H O H 2 Acid Base
H3C-C-0-H+H-0:÷H2C-C-0:+H-O+-H H Acid Base H3C-C-0-H +:O-H H3C=C-O:+H—0-H Acid Base 3.3 THE STRENGTH OF ACIDS AND BASES: KaAND pKa When acetic acid dissolves in water, the following reaction dose not proceed to completion H3C-C-0-H HO H3C-C-0 H3o
H O + H + H O H H Acid Base H3 C C O O H H3 C C O O + H O H Acid Base H3 C C O O H H3 C C O O + - + - O H 3.3 THE STRENGTH OF ACIDS AND BASES: Ka AND pKa When acetic acid dissolves in water, the following reaction dose not proceed to completion: H3 C C O O H H3 C C O + H O 2 O + H3 O +
3.3A THE ACIDITY CONATANT Ka Experiments show that in a 0. IM solution of acetic acid at 25C only about 1% of the acetic acid molecules ionize by transferring their protons to water. The reaction is a equilibrium, we can describe it with an expression for the equilibrium constant H3O] [CH3CO21 Kcq=TCH3CO2田2O For dilute aqueous solutions, the concentration of water is essentially constant, so the equilibrium constant can be expressed with the acidity constant(Ka) Ka= Kea hoi=i H3O][CH3CO CH3CO2H
Experiments show that in a 0.1M solution of acetic acid at 25℃ only about 1% of the acetic acid molecules ionize by transferring their protons to water. The reaction is a equilibrium, we can describe it with an expression for the equilibrium constant. For dilute aqueous solutions, the concentration of water is essentially constant, so the equilibrium constant can be expressed with the acidity constant (Ka). Keq [H2 O] = [H3 O + ] [CH3 CO2 - ] [CH3 CO2 H] Ka = Keq = [H3 O + ] [CH3 CO2 - ] [CH3 CO2 H] [H2 O] 3.3A THE ACIDITY CONATANT Ka