ORGANIC CHEMISTRY 4.docx

**Definition**: It is branch of chemistry that studies carbon compounds present in living things, once living thing or synthetic (man-made). Compounds that make up living things whether dead or alive largely contain carbon. Carbon forms characteristic stable covalent bonds with itself and many othe...

**Definition**: It is branch of chemistry that studies carbon compounds present in living things, once living thing or synthetic (man-made). Compounds that make up living things whether dead or alive largely contain carbon. Carbon forms characteristic stable covalent bonds with itself and many other non-metals like hydrogen, nitrogen, oxygen and halogens to form a variety of compounds. **This is because**: 1. Carbon uses all four valence electrons to form four strong covalent bonds 2. Carbon can covalently bond to form a single very long chain or ring. 3. Carbon can covalently bond to form a very long chain or ring. **Hydrocarbons:** Definition: Are group of organic compounds containing hydrogen and carbon atoms only. They are formed by covalent bonding between hydrogen and carb atoms. According to types of bonds, hydrocarbons are classified into three: a. Alkanes (single bond) b. Alkenes (double bond) c. Alkynes (Triple bond). **Uses of hydrocarbons:** 1. Natural gases E.g. Methane, propane, butane and hexane are all hydrocarbons. 2. Plastics 3. Wax 4. Some common medical drugs a. **Alkanes:** Naming alkanes: General formula: **C~n~H~2~n+2** where n= number of carbon atoms in molecule. Structural formula: Chemical Structure of Methane ethane propane butane, Anatomy Of Methane ethane propane butane, Chemical formula of Methane ethane propane butane Stock Vector Image & Art - Alamy Naming of the alkanes, prefix and suffix are used. The prefix depicts the number of carbon atoms in their structure while the suffix depicts their series. n Prefix Suffix Name General formula --- -------- -------- --------- ----------------- 1 Meth ane Methane CH4 2 Eth ane Ethane C2H6 3 Prop ane Pentane C3H8 4 But ane Butane C4H10 5 Pent ane Pentane C5H12 6 Hex ane Hexane C6H14 7 Hept ane Heptane C7H16 Note: Alkanes above different by -CH2- unit. They form a common series that show similarity in chemical reactions and a trend in their physical properties. Such series are called **homologous series.** **The IUPAC system of nomenclature (naming) follows basic rules:** 1. Identify the longest continuous carbon chain determining parent chain. 2. Identify the substituent groups. 3. Number the longest chain from end of the chain near branch. Branched group gets the lowest number. 4. Determine the position and type of branched group i.e. methyl, ethyl, propyl etc. according to number carbon attached. 5. Use prefix di-,tri-,tetra to show the number of branched groups attached to the parent alkane. 1. **2-Methylbutane** (CH~3~CH(CH~3~) CH~2~CH~3~  2. **2,2-dimethylpentane** **\ \ ** **Occurrence and extraction of alkanes** **This is done by:** - **Fractionating column** - **Fractional distillation (takes place in tall tower called fractional tower or column).** **Cracking of alkanes: this is the breaking of the long chain alkanes into those of smaller molecules.** **Heating/catalyst** **CH~3~CH~2~CH~3~ CH~4~ +CH~2~=CH~2~ + H~2~** **Pr**eparation and properties of Methane and Ethane Preparation of methane: It is prepared in laboratory by heating mixture of sodium ethanoate and soda lime. Sodium hydroxide in the mixture reacts with sodium ethanoate to form methane gas and sodium carbonate. Sodium ethanoate + Soda lime Methane + Sodium carbonate CH~3~COONa (s) + NaOH (s) CH4(g) +Na~2~CO~3~ (s) Physical properties of Methane: - Colourless gas - Odourless gas - Denser than air - Insoluble in water but soluble in organic solvents **Preparation of Ethane** Ethane also undergoes the same reactions as such combustion and substitution that like methane. **Chemical Properties of methane** The strong Carbon-Carbon and Carbon-Hydrogen covalent bonds make the alkanes relatively unreactive. 1. **Combustion of methane** CH4 (g) + 2O~2~ (g) CO~2~ (g) + 2H~2~O(l) 2. **Substitution reactions of methane**: U.V CH4 + Cl~2~ CH3Cl + HCl (g) **Uses of Alkanes** - Most alkanes are used as fuel. Methane is used as biogas at homes. Butane is mainly used as laboratory gas. - Cracking of long chains alkanes is used as a major source of hydrogen gas for the manufacture of ammonia - Alkanes are in use in the manufacture of carbon-black which is found in printer's ink. - Used in manufacture of useful industrial chemicals like methanol, ethanol, and chloromethane. b. **Alkenes**: are unsaturated hydrocarbons with one double bond any two carbon atoms in their structure. General formula: **C~n~H~2~n.** Examples: Ethene (C~2~H4**): CH~2~=CH~2~** Propene (C~3~H~6~): CH~2~=CH-CH~3~ **Preparation of Ethene gases** 1. Reaction of alcohol with concentrated sulphuric acid Ethanol + conc. suphuric acid Ethyl hydrogensulphate + Water C~2~H~5~OH(l) + H~2~SO~4~ C~2~H~5~SO~4~(l) + H~2~O (l) Ethyl hydrogensulphate +heat Sulphuric acid + ethene C~2~H~5~HSO~4~(l) + heat (170◦C) H~2~SO~4~(aq) + C~2~H~4~ (g). 2. Cracking hydrocarbons in industry **Physical properties of Alkene** Ethene is colourless gas, has no smell and is insoluble in water **Chemical properties of alkenes** a. Burning/combustion b. Addition reactions I. Hydrogenation: addition of hydrogen in presence of nickel as catalyst. This leads to formation of solid fats in major industrial application of converting liquid edible oils. Ni/170◦C H~2~C=CH~2~ + H~2~ H~3~C-CH~3~ Hydrogenation is used to harden oils to solid fat especially margarine. II. Halogenation: is addition of halogens (fluorine, chlorine, bromine or iodine ) to form alkane. H~2~C=CH~2~ + Br~2~ BrCH~2~-CH~2~Br III. Reaction with bromine water: alkenes decolorize bromine water. This reaction is used as test for unsaturated compounds. H~2~C=CH~2~ + Br~2~ (l) BrCH~2~-CH~2~Br IV. Polymerization: Addition polymerization is the process where a small unsaturated monomer alkene e.g ethene molecule can join together to form a large saturated molecule. **Example formation of polyethene**  Uses of alkenes - Manufacture of plastic (polyethene) - Hydrolysis of ethene to manufacture ethanol in industry - In ripening fruits - In detergents manufacturing. C. **Alkynes** **General formula: C~n~H~2~n-2** **Structural formula:** Acetylene Formula - Chemical and \... **Nomenclature(naming):** The names of all alkynes end with -yne. The names are derived from respective alkanes where 'a' is replaced by 'y' as follows: - Ethane becomes Ethyne - Propane becomes Propyne - Butane becomes Butyne - Hexane becomes Hexyne **Systematic (IUPAC) naming of alkynes** **Rules for naming branched alkynes** a. Determine the longest continuous chain of carbon atoms that has triple bond between two carbon atoms. This gives parent name of the compound. b. Number the carbons in the chain so that the triple bond would be between the carbon atoms with the lowest numbers. c. Identify and name the branching groups attached to this continuous chain of carbon d. Write the number of carbons bearing the branching group in front of the parent's name followed by a hyphen (\_\_\_). e. Look at two carbon atoms between which the triple bond is located. Identify carbon atom which has the lowest number.  **Uses of alkynes:** - Ethyne burns in oxgen to give a very luminous flame. This is why it is used to produce light in lamps. - Ethyne is used in oxy-acetyne flame for metal cutting and welding - Some alkynes are used for manufacture of plastics ,synthetic rubbers,synthetics fibres ,adhesives and other things. **Isomerism:** is existence of compounds having the same molecular formula but different structural formulae. **Isomers**: are compounds with the same molecular formula but different structural formulas(e). **Isomers of alkanes:** CH~3~CH~2~CH(CH~3~) CH~3~ and CH~3~C(CH~3~)~2~CH~3~ Both compounds have same molecular formula: C~5~H~10~ but have different structural formulae. **Isomers of Alkenes**: There are two types of alkene isomers: a. Branching isomerism: it occurs when substituent group is attached to one of the carbon atom in the longest chain containing double bond. Example: in pentene i. CH~3~CH~2~CH=CHCH~3~ or What is the structural formula of 2 Pentene? Pent-2-ene ii. CH~3~CH~2~CH=CH~2~ or  3-methylbut-1-ene b. **Positional isomerism:** occurs when the position of the double bond shifts in an alkenes. For example: 1. CH~2~=CHCH~2~CH~3~ Pen-1-ene. 2. CH~3~CH=CHCH~2~CH~3~ Note: only position of the double bond changes in positional isomerism. **Isomers of Alkynes:** there are two types of isomerism. 1. **Chain isomerism**: occurs when carbon atoms are in a continuous chain Draw and name all the possible pentyne isomers, \$\\mathrm{C}\_ \| Quizlet  2. **Position isomerism**: There are two types of isomers of Pentyne depending on where the triple bond is: Pent-1-yne and Pent-2-yne Good luck!!! By:T/Guot Jongkor