Organic Chemistry: Key Concepts and Reactions, Lecture notes of Organic Chemistry

Download Organic Chemistry: Key Concepts and Reactions and more Lecture notes Organic Chemistry in PDF only on Docsity! 1 Saturday X-tra X-Sheet: 10 Organic Reactions Key Concepts This lesson will focus on the following: • Substitution reaction • Combustion • Hydrogenation • Halogenation • Hydrohalogenation • Hydration • Elimination reaction Terminology & definitions • Substitution reaction – is a chemical reaction in which an atom or a group of atoms in a molecule are replaced or substituted by another atom or group of atoms. • Combustion – is a chemical reaction in which a substance reacts rapidly with oxygen and produces heat and light. • Addition reaction – is a chemical reaction where a molecule attaches to the double or triple bond of a second molecule to form a single molecule. During the reaction the double or triple bond is broken and new atoms are added to the molecule to form a more saturated product. • Hydrogenation – is the addition reaction that takes place when hydrogen gas(H2) is added to an unsaturated hydrocarbon (alkenes or alkynes) in the presence of a suitable catalyst (e.g. Ni, Pt or Pd). • Halogenation – is the addition reaction that takes place if a halogen is added to an unsaturated hydrocarbon. • Hydrohalogenation – is the addition of anhydrous hydrogen halides to produce alkyl halides. • Hydration – is the addition of water in an unsaturated hydrocarbon in the presence of a catalyst to produce an alcohol. • Elimination reaction – is the removal of a small molecule from a big molecule. X-planation of key concepts and terminologies Substitution A substitution reaction is a chemical reaction in which an atom or group of atoms in a molecule are replaced or substituted by another atom or group of atoms. The process of substitution is only possible under two conditions, in the presence of sunlight or ultra-violet light and at a temperature between 2500C and 4500C. In the alkanes the hydrogen atom is displaced by a halogen atom to form two products of which one is a haloalkane/alkyl halide. This reaction is thus called substitution reaction through the process of halogenation. CH4(g) + CI2(g) hf CH3CI(g) + HCI(g) ∆ 2 Combustion Combustion is a chemical reaction in which a substance reacts rapidly with oxygen and produces heat and light. All combustion reactions are exothermic. Hydrocarbons undergo combustion to form CO2(g) and H2O(g). CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + energy 2C2H2 + 5O2 → 4CO2 + 2H2O + energy Addition Unsaturated compounds undergo addition reactions to form saturated compounds. When a double or triple bond breaks, other atoms are added to the chain. Addition reactions, which occur at unsaturated hydrocarbons, happen faster than substitution reactions which occur at saturated hydrocarbons, and this difference in rate can be used to test whether a hydrocarbon is saturated or unsaturated. Hydrogenation Hydrogenation is the addition reaction that takes place when hydrogen gas (H2) is added to an unsaturated hydrocarbon in the presence of a suitable catalyst (e.g. Ni, Pt, or Pd). It is used in producing margarine. CH2 ═ CH2 + H2 → CH3 – CH3 Halogenation Halogenation is the addition of halogens X2 (X = CI, Br, I). Br Br │ │ H-C≡C-H + Br2 → H - C═C - H + Br2 → H - C – C - H │ │ │ │ Br Br Br Br Hydrohalogenation Hydrohalogenation, is the addition of HX (X = CI, Br, I) in the presence of water. CH2 ═ CH2 + HCI → CH3 – CH2CI During addition of HX to unsaturated hydrocarbon, the H atom attaches to the C atom which already bears the greater number of H atoms. The X atom attaches to the C atom bearing the smaller number of H atoms. Hydration Hydration is the addition of water to a hydrocarbon in the presence of a catalyst. CH2 ═ CH2 + H2O → CH3-CH2OH