An Introduction to Organic Reactions and Their Mechanism Acids and Bases

Acid-Base Reaction

Acid-Base properties Acid Properties: When dissolved in water, acids Conduct electricity Change blue litmus to red Have a sour taste React with bases to neutralize their properties React with active metals to liberate hydrogen. Base Properties: When dissolved in water, bases Conduct electricity Change red litmus to blue Have a slippery feeling React with acids to neutralize their properties.

3.1 Reactions and Their Mechanism Chemical equation: Reactants  products Atoms are neither created nor destroyed. Four categories: substitution, additions, eliminations and rearrangement

Substitution Substitution: one group is replaced with another General reaction

Elimination Atoms or groups are removed from adjacent atoms to form a double or triple bond General reaction

Addition Atoms or groups add to adjacent atoms of a multiple bond General reaction

Rearrangement A molecule undergoes a reorganization of its constituent parts. Positions of the double bond and a hydrogen atom changed

3.1Homolysis and Heterolysis of Covalent Bonds When an organic reaction occurs, some covalent bonds must be break and a new bond must form. A covalent bond can be broken in two ways: Heterolysis Bond cleavage in which bonding of electrons are unevenly divided between the two parting atoms Homolysis Bond cleavage in which bonding of electrons are evenly divided between the two parting atoms

Homolysis and Heterolysis

3.2 Acid-Base Reactions Bronsted-Lowry acids: an acid is a substance that can donate a proton (H+) Bronsted-Lowry acids: an base is a substance that can accept a proton (H+)

The Lewis Definition of Acids and Bases Lewis acid is (electrons acceptor) electrophiles Lewis base is (electrons donor) nucleophiles

Lewis acids and bases

Lewis Acids -Bases

Combination of Site Type The reaction site is A polar bond because oxygen is more electronegative than carbon A Lewis base since there are unshared pairs of electrons to the oxygen that can be shared with a Lewis acid Multiple bond with a π bond in which electrons are available to incoming species

Examples Which of the following are potential Lewis acids and which are potential Lewis base? Identify Lewis Base site

Examples Write equations showing the Lewis acid-base reaction that take place when: Methanol (CH3OH) reacts with BF3

Heterolysis of Bonds to Carbon: Carbocations and Carboanions

Carbocations and Electrophiles Electrophiles are reagent which in their reactions seek the extra electrons that will give them a stable valence of electrons

Carbocations and Nucleophiles Nucleophiles are reagents that seek a proton or some other positive center

Examples Classify the following as either electrophiles or nucleophiles Use the curved-arrow notation to write the reaction what would take place between dimethylamine (CH 3 ) 2 NH and boron trifluoride). Identify Lewis acid and Lewis Base

16.2 Acid Strength Strong acids: completely ionized or completely dissociated Forward reaction is predominated Most of HA is dissociated Conjugated base is weak and has low attraction for proton HA(aq) + H 2 O(l)  H 3 O + (aq) + A - (aq)

Acids Strength Weak acids: partially ionized or dissolved Reverse reactions is predominated Most of HA is undissociate Conjugated base is strong and has high attraction for proton HC 2 H 3 O 4 (aq) + H 2 O(l) H 3 O + (aq) +C 2 H 3 O 4 - (aq)

Acid Strength