Organic Reactions

Major Terminology Associated with Organic Reactions Substrate…organic reactant being modified by the reagent. 2. Reagent…inorganic or organic reactant that modifies the substrate. Solvent…medium that dissolves the reactants. Catalyst…substance that reduces the amount of energy needed to start a reaction but is not part of the reaction. Condition…the physical or physicochemical quantity used in the reaction.

A Single Step Chemical Equation

Example of a Single Step Chemical Eqn.

Addition Reactions Double and triple bonds are weaker than single bonds More reactive In the addition reaction, reactants are added to the carbon atoms in the double or triple bond.

Addition Reactions

Addition Reactions H2C=CH2 + A—B  H2C—CH2 A B

Hydrogenation In hydrogenation, hydrogen atoms add to the carbon atoms of a double bond or triple bond. A catalyst such as Pt or Ni is used to speed up the reaction.

Hydrogenation of Oils When hydrogen adds to the double bonds in vegetable oils, the products are solids at room temperature.

Halogenation In halogenation, halogen atoms add to the carbon atoms of a double bond or triple bond.

Testing for Double and Triple Bonds When bromine (Br2) is added to an alkane, the red color of bromine persists. When bromine (Br2) is added to an alkene or alkyne, the red color of bromine disappears immediately.

Hydrohalogenation In hydrohalogenation, the atoms of a hydrogen halide add to the carbon atoms of a double bond or triple bond.

Markovnikov’s Rule When an unsymmetrical alkene undergoes hydrohalogenation, the H in HX adds to the carbon in the double bond that has the greater number of H.

Hydration Adds Water In hydration, H and OH from water add to the carbon atoms of a double bond or triple bond to form alcohols (OH). The reaction is catalyzed by acid H+.

Elimination Reactions

In an elimination reaction, two groups X and Y are removed from a starting material. Two  bonds are broken, and a  bond is formed between adjacent atoms. The most common examples of elimination occur when X = H and Y is a heteroatom more electronegative than carbon.

Elimination is the opposite of addition .

Substitution Reactions

Substitution reactions involve  bonds: one  bond breaks and another forms at the same carbon atom. The most common examples of substitution occur when Z is a hydrogen or a heteroatom that is more electronegative than carbon.

Practice Exercises Classify the following reactions as substitution, elimination, or addition.

Bond Dissociation Energy

Bond Dissociation Energy

Stronger bonds have a higher ΔHº

Calculating ΔHº Using Bond Dissociation Energy

Which has the higher bond dissociation energy? H-Cl or H-Br b) c)