TYPES OF ORGANIC CHEMICAL REACTIONS

Categories of Simple Organic Reactions Substitution Addition Condensation/elimination Hydrolysis Mild oxidation & strong oxidation Combustion Acid/base reactions

Substitution Reactions A substitution reaction occurs whenever one atom of an organic molecule is replaced by another. Substitution reactions often require heat and/or a catalyst in order to occur. Example: Substitution of an alkane H H H C H + Cl2 H C Cl + HCl H H

Substitution of Benzene Due to the strong bonding arrangement between the carbon atoms in a benzene ring, the ring cannot be easily broken during chemical changes. The hydrogen atoms that are bonded to each carbon can be substituted for other atoms and groups. Examples: H Br + HBr + Br2 + HNO3 NO2 + H2O TNT synthesis…

Addition Reactions In addition reactions, new atoms or groups are bonded to the atoms of an organic molecule. The organic molecule must be unsaturated to start with (double or triple bonds!) New bonds can be made to the carbon atoms involved in the double or triple bond if the part of the bond is first broken. I’m now ready to make more bonds! C H CH2=CH2

Some Simple Addition Reactions C=C H + H2  H-C-C-H (a.k.a. “hydrogenation”) C=C H + HCl  H-C-C-Cl C=C H + H2O  H-C-C-OH (a.k.a. “hydrolysis”)

Markovnikov’s Rule If the double or triple bond is part of a molecule with three or more carbon atoms in the chain, the most likely addition reaction products can be predicted using a rule first formulated by the Russian chemist V.V. Markovnikov. Markovnikov’s Rule …the more electronegative atom will predominantly bond to the carbon atom of the double bond that has fewer hydrogen atoms.

Markovnikov’s Rule º - Eg.1 H OH H C=C-CH3 + H2O  H- C - C- CH3 Eg.2 It should be mentioned that the primary alcohol (1-propanol) is also a possibility, but it would be produced in a much lower proportion than the 2-propanol shown above. Eg.2 H-C C-CH2-CH3 º + 2HCl  - Cl H Most favoured product!

Condensation/Elimination Reactions Organic compounds containing hydroxyl or carboxyl groups can combine by eliminating a molecule of water between them. An ether is created! Example 1- condensation of two alcohols H-C - C-O-H H H-O-C - C-H H H-C - C-O-C–C-H H + H2O + Molecule of H2O is formed

Condensation/elimination When an alcohol reacts with a carboxylic acid to eliminate a molecule of water between them, the resulting bond creates an ester linkage as shown below: We’ve created an ester H-C - C-O-H H O + H-O-C – CH2-CH3 CH2-CH2- O- C-CH2-CH3 O If excess water is added to an ester, the reaction will reverse itself. + H2O

Uses of Esters Demo! Esters often have characteristic flavours and aromas which allows them to be used in food products. Methanol + butanoic acid  methyl butanoate (apples) Octanol + acetic acid  octyl acetate (orange) Benzyl alcohol + butanoic acid  phenyl butanoate (flowers) Pentanol + acetic acid  pentyl acetate

Condensation/elimination If a molecule of water is eliminated from within a single molecule, an unsaturated compound is formed and the molecule is said to be “dehydrated.” H + H H H OH H H2O

Oxidation Reactions In the terminology of organic chemistry, when a molecule is oxidized, the number bonds to oxygen atoms increases within the molecule. Oxidizing agents are varied: CrO3/H+, KMnO4, K2Cr2O7 Often, the oxidizing agent is represented simply as “O” over the reaction arrow:

Oxidation Reactions Mild Oxidation Strong Oxidation alcohol aldehyde H CH3-C-OH H CH3-C-H O ethanal ethanol Strong Oxidation alcohol Carboxylic acid CH3-C-OH H O Ethanoic acid

Oxidation Reactions Strong Oxidation cont’d… Secondary alcohols require a strong oxidizing agent and can only be oxidized to ketones. CH3-C-CH2-CH3 H OH 2-butanol CH3-C-CH2-CH3 O butanone

Combustion BOOM! All organic compounds can be combusted or burned. Carbon dioxide gas and water vapour are the products of hydrocarbon combustion. Combustion is really a type of very extreme oxidation reaction where O2(g) is the oxidizing agent. 2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g) CH3-CH2-OH(l) + 3O2(g)  2CO2(g) + 3H2O(g)