Organic Reactions Types of Reactions

There are 9 main types of reactions we will examine: 1.Combustion 2.Substitution 3.Addition -Halogenation, Hydrogenation, Hydrohalogenation, Hydration 4.Dehydration (reverse of hydration) 5.Condensation 6.Esterification (type of condensation) 7.Hydrolysis (reverse of esterification) 8.Oxidation (Controlled) 9.Reactions with Amines

Organic Reactions Flow Chart

1. Complete Combustion Reaction in which a compound reacts with oxygen to produce the oxides of elements that make up the compound Some energy (activation energy) is required to start combustion, but once it overcomes it, the reaction is spontaneous and releases a lot of energy Hydrocarbons and alcohols undergo combustion

1. Complete Combustion Hydrocarbon or Alcohol + O 2  CO 2 + H 2 O Example: C 3 H 8 + 5O 2 (g)  3CO 2 (g) + 4H 2 O(g) + energy 2CH 3 CH 2 CH 2 OH(l) + 9O 2 (g)  8H 2 O (g) + 6CO 2 (g) + energy

2. Substitution Reaction in which a hydrogen atom or functional group is replaced by a different atom or functional group Alkanes undergo substitution reactions Alkanes are relatively unreactive, thus a lot of energy is required (UV light) to catalyze rxn Alkanes react with chlorine and bromine to form haloalkanes

2. Substitution Alkane + halogen  haloalkane + hydrogen halide Example: CH 4 + Cl 2  CH 3 Cl + HCl CH 3 Cl + Cl 2  CH 2 Cl 2 + HCl CH 2 Cl 2 + Cl 2  CHCl 3 + HCl CHCl 3 + Cl 2  CCl 4 + HCl

3. Addition Reactions Reaction in which two molecules form to make a single molecule. This occurs with the carbon-carbon double or triple bonds of alkenes and alkynes Alkenes and alkynes are involved in 4 types of addition reactions: 1.Halogenation (adding halides) 2.Hydrogenation (adding hydrogen) 3.Hydrohalogenation (adding hydrogen halides) 4.Hydration (adding water)

A. Halogenation (of an alkene) Alkene + halogen  haloalkane Example:

A. Halogenation (of an alkyne) Alkyne + halogen  haloalkane Example: In the presence of excess halogen, a haloalkane is formed from a alkyne

B. Hydrogenation (of an alkene) Alkene + hydrogen  alkane Example

Alkyne + hydrogen  alkane Example: Step Reactions for an alkyne B. Hydrogenation (of an alkyne)

B. Hydrogenation (of a cycloalkene) Cycloalkene + hydrogen  cycloalkane Example:

C. Hydrohalogenation (adding hydrogen halides) Alkene + hydrogen halide  haloalkane Example:

Markovnikov’s Rule When 2 non-identical atoms are added to an alkene or alkyne, two possible products may form How do we predict which product? Markovnikov’s Rule: “The rich get richer…”

Example: Markovnikov’s rule Things to Consider about Markovnikov’s rule: -Small quantities of the other product are produced -If both carbon atoms have the same number of hydrogen atoms, the products will be Chemists have developed strategies to change the outcome by using catalysts or changing other reaction conditions.

Practice: Using Markovnikov’s Rule Predict the major product of the following addition reaction. a) b)

D. Hydration (adding water) Alkene + water  alcohol Example: Markovnikov’s Rule also applies to hydration due to the asymmetry

4. Dehydration A reaction that involves removal of a hydrogen atom and a hydroxyl group, producing a smaller molecule and water The reverse of the addition (hydration) reaction Alcohols are dehydrated to alkenes using sulfuric acid (H 2 SO 4 )

4. Dehydration of 1° Alcohols 1° Alcohol  alkene + water Example: H 2 SO 4

4. Dehydration of 2° and 3° Alcohols In dehydration reactions of 2 and 3 alcohols with more than 3 carbons, more than one alkene may be produced Example: Predicting the major product is beyond the scope of this course

5. Condensation Reaction in which two molecules combine to form a larger molecule and a small, stable molecule, usually water, as a second product Look for an OH - group from one molecule and a H + from a second molecule being removed to form a water – Alcohols (in presence of H2SO4) condense to form ethers – Carboxylic acids (-COOH) and amines (-NH 2 ) form amides (-CONH 2 )

5. Condensation (producing ethers) Alcohol + Alcohol  Ether + water Example: H 2 SO 4

5. Condensation (producing amides) Carboxylic acid + Amine  Amide + water Example:

Specifically, carboxylic acids react with either ammonia, 1° amines or 2° amines This will produce 1° amides, 2° amides or 3° amides

6. Esterification (condensation) Reaction of a carboxylic acid with an alcohol to form an ester and water Flavours and smells of fruits and spices are due to ester compounds Catalyzed by a strong acid Can be duplicated in a lab

6. Esterification (condensation) Carboxylic Acid + Alcohol  Ester + water Example: Conc. H 2 SO 4

7. Hydrolysis Reaction in which a molecule is broken apart by adding OH- from a water molecule to one side of a bond and H+ atom of same water molecule to other side of bond This is the reverse of a condensation reaction (we will look at the reverse of esterification) When esters are treated with an acid or base, hydrolysis occurs

7. Hydrolysis Ester + acid/base  Carboxylic Acid + Alcohol Example: (Ionized as a salt)

8. Oxidation Reaction in which a molecule reacts with an oxidizing agent. Oxidizing agents are oxygen-rich compounds that increase the number of C-O bonds in a molecule. Aldehydes and ketones are produced by the “controlled” oxidation of alcohols Oxidation agents such as potassium dichromate (K2Cr2O), hydrogen peroxide (H2O2) and potassium permanganate (KMNO4) supply the oxygen Considered “controlled” because the reactant is not completely oxidized due to a limited quantity of oxygen present Complete oxidation reactions would be combustion reactions

8. Oxidation (of 1° Alcohols) Step 1: 1° Alcohol + [O]  Aldehyde + water Step 2: Aldehyde + [O]  Carboxylic acid Example:

8. Oxidation (of 2° Alcohols) 2° Alcohol + [O]  Ketone + water Example: 3° Alcohols do not undergo oxidation due to a lack of hydrogen on the adjacent carbon. This prevents the formation of water.

9. Reactions with Amines Reactions in which amines can be synthesized using alkyl halides The reactions vary depending on whether a 1°, 2° or 3° amines is being produced These reactions are reversible: amides can be hydrolized in acid/bases to produce the carboxylic acid and the amine

9. Reactions with Amines (forming 1° Amines) Alkyl halide + ammonia  1 Amine + hydrogen halide Example:

9. Reactions with Amines (forming 2° Amines) Alkyl halide + 1° Amine  2° Amine + hydrogen halide Example:

9. Reactions with Amines (forming 3° Amines) Alkyl halide + 2° Amine  3° Amine + hydrogen halide Example:

Practice Problems for Organic Reactions Chapter 1 Review (starting on page 72) - #22ab, 30bcf, 31, 35, 39bdfg, 40ceghj, 41adfgj, 44