Organic Reactions

Reactions of Alkenes and Alkynes

Organic Reactions of Hydrocarbons Millions of reactions take place everyday in the trillions of cells in your body. Living organisms are comprised of organic compounds. Many reactions occur in the cells of your body therefore we need to understand how they transpire.

The 4 Types Of Addition(unsaturated) Reactions There are four types of addition reactions: Hydrogenation Halogenation Hydrohalogenation Hydration The general equation for an addition reaction is: A + B C Notice that C is the final product with no A or B remaining.

Addition Reactions Addition reactions involve the addition of one or more particles to an organic molecule. These reactions occur with unsaturated hydrocarbons (i.e. alkenes and alkynes) unsaturated hydrocarbons are organic molecules that contain at least one double or triple bond in their parent carbon chain. Examples of unsaturated hydrocarbons

Hydrogenation Reaction (Type 1) In this reaction, the DB is broken and replaced with hydrogen gas (H2(g)) whereby one H is added to each carbon (the unsaturated hydrocarbon). The hydrogen gas is under high temperature and pressure. EXAMPLE: Hydrogenation provides many food industry benefits such as longer shelf life. Makes food easier to handle and store. The overall cost of food is also lower. However, consumption of excess hydrogenated oils can cause health problems such as atherosclerosis, which is the hardening of the artery walls in your body.

Reactions of Alkenes & Alkynes Hydrogenation reactions can occur with alkenes, alkynes and cyclic alkenes Note: This is not the case for benzenes and phenyls. They undergo a different type of reaction (substitution reactions).

Halogenation Reactions (Type 2) Addition Reactions can also occur with halogens whereby the unsaturated bond (double/triple) is broken and replaced with the halogen (F2, Br2, I2 and Cl2) hydrogen chloride, or water. The DB is broken and replaced with the halogens. Halogenation reaction – a halogen such as bromine or chlorine reacts with an alkene or alkyne and produces an alkyl halide The halogenation of an alkyne produces a halogenated alkene or if excess halogen is present, an alkyl halide.

Halogenation Reactions Continued Halogenation reactions are extremely common in manufacturing factories. One huge drawback of the halogenation reaction is that they can produce chlorofluorocarbons (CFC’s). Chlorofluorocarbons are also commonly known as Freon's and were first developed in 1930’s. They were widely used, especially in all types of cooling devices because they are non flammable, non toxic, cheap, evaporated and condensed easily. However, Freon depletes the ozone layer. The ozone layer is a crucial part of our atmosphere which absorbs ultraviolet (UV radiation). One Freon molecule has ability to destroy one thousand ozone molecules.

Hydrohalogenation Reaction (Type 3) This is the combination of a halogen atom with a hydrogen and is termed a hydrogen halide. Examples include hydrogen fluoride (HF), hydrogen bromide (HBr), and hydrogen chloride (HCl). Hydrogen halides can combine with unsaturated hydrocarbon to produce alkanes. The reaction involves the breaking of the DB and replacing it with H on the first carbon and the halogen on the second carbon.

Hydration Reactions (Type 4) This reaction occurs when water reacts with an alkene or alkyne. This forms a type of organic compound that contains a hydroxyl group (-OH). This compound is called an alcohol The DB is broken and replaced with a H on the first carbon and the OH on the second carbon. Ethene reacts with water to produce ethanol

Markovnikov’s Rule Markovnikov’s rule : “The Rich Get Richer” The rule for predicting the products of addition reactions: when a hydrogen halide or water is added to an alkene, the hydrogen atom generally bonds to the carbon atom within the double bond that already has more hydrogen atoms bonded to it. Major Product Minor Product

Practice Drawing Major and Minor Products

Aromatic Reactions

Reactions of aromatic compounds Aromatic compounds are much less reactive than alkenes but are more reactive than alkanes. Benzene rings therefore do not normally go under hydrogenation reactions like alkenes and alkynes do. Benzene undergoes SUBSTITUTION REACTIONS Substitution reactions are a reaction in which a hydrogen atom is replaced by another atom or group of atoms. This type of reaction usually involves alkanes or aromatics with halogens to produce organic halides and hydrogen halides. Substitution reactions - When hydrogen atoms are replaced by other atoms such as halogens

Alkane Substitution Aromatic Substitution Step 1- 2 hydrogens are removed from the alkene/benzene Step 2- replace one of the H with a halogen to form one of the final products Step 3- Combine the second H with the other halogen to form a second final product

Reactions of cyclohexane, benzene and cyclohexene Substitution Reaction Substitution Reaction Addition Reaction

Alcohols and Ethers Reactions

Reactions Involving Alcohols Recall from 1.2 that many alcohols are manufactured by addition reactions. Alcohols can be broken down through dehydration reactions which is the opposite of addition reactions. Dehydration reaction– is a reaction that involves the removal of a hydrogen atom and a hydroxyl group from the reactant. atoms are removed from a molecule to form a double bond • one reactant breaks up to give two products (reverse of Addition Rxn)

Reactions of Ethers Ethers can be synthesized from the condensation reaction of alcohols. Condensation reactions occur when 2 molecules combine to form a larger molecule and water.

Condensation Reaction A condensation reaction when a hydroxyl group (OH) and an H atom are removed. This reaction is the basis by which living organisms build tissue from their food they consume in their diet. For example, living organisms convert the simple sugar glucose into the larger storage molecule glycogen by condensation reactions. In humans, glycogen is stored in the liver and muscle tissue where it is readily available for energy use.

Proteins are also formed from condensation reactions between amino acids

Condensation Continued In condensation reactions, water is removed from the reactants. Proteins have many important roles in biological systems and build important structures. Many important organic compounds such as ester and ethers are also formed from condensation reactions.

Aldehydes and Ketone Reactions

Reactions Involving Aldehydes and Ketones Aldehydes and Ketones are synthesized by the controlled oxidation of alcohol. Oxidizing agents are oxygen-rich compounds such as potassium dichromate K2Cr2O, hydrogen peroxide H2O2 and potassium permanganate KMnO4. Usually [O] is used to represent the oxidizing agent

Reactions Continued

Hydrogenation of Aldehydes and Ketones Recall that hydrogenation involves the addition of hydrogen to another molecule. The double bond is broken and the result is an alcohol. The hydrogenation of a aldehyde produces a primary alcohol The hydrogenation of a ketone produces a secondary alcohol.

Hydrogenation continued

Carboxylic Acids and Ester Reactions

Reactions Involving Carboxylic Acids and Esters Formation of Carboxylic Acids – Oxidation of aldehydes Formation of Esters – Esterfication (alcohol + Carboxylic Acid)

Reactions Continued Breakdown of an Ester – Hydrolysis (addition of water) ethyl propanoate water propanoic acid (carboxylic acid) ethanol (alcohol)

Amines and Amides Reactions

Reactions Involving Amines Synthesis of Amines (substitution) General Reaction + HCl Example: Reaction of Alkyl halide with Ammonia + HCl Reaction of Alkyl Halide with a Primary Amine + HCl

Reactions Involving Amides Formation of Amides – Condensation reaction (carboxylic acid and ammonia, primary or secondary amine) The following reactions are also reversible if an amide is put through a hydrolysis reaction similar to that of esters it would form an amine and carboxylic acid