Organic Chemistry PDF

Organic Chemistry Organic Chemistry It is the chemistry of specific carbon compounds except oxides, carbonates and carbides. Hydrocarbons Organic compounds composed of carbon and hydrogen only. Examples: Methane (CH4), ethane (C2H6) Unique Nature of Carbon Tetravalency of Carbon  Carbon forms...

Organic Chemistry Organic Chemistry It is the chemistry of specific carbon compounds except oxides, carbonates and carbides. Hydrocarbons Organic compounds composed of carbon and hydrogen only. Examples: Methane (CH4), ethane (C2H6) Unique Nature of Carbon Tetravalency of Carbon  Carbon forms four covalent bonds by mutually sharing its four electrons with other atoms.  It is hence tetravalent or exhibits tetravalency. Catenation  It is the tendency of an element to form chains of identical atoms.  Catenation is maximum in carbon because the value of the C–C bond energy is maximum.  Carbon undergoes self-linking forming straight, branched and closed chains.  Catenation and tetravalency also result in the formation of single, double and triple bonds. Classification of Organic Compounds Homologous Series It is a group of organic compounds with a similar structure and similar chemical properties in which the successive compounds differ by a CH2 group. Characteristics of a homologous series i. Each member of the series differs from the preceding one by the addition of a CH2 group and by 14 amu. ii. All members of a homologous series share a general formula. For example, the general formula for alkane is CnH2n+2 and that for alkene is CnH2n. iii. The physical properties of the members show gradation in properties as molecular mass increases. iv. The chemical properties also show gradient similarity. For example, methane and ethane react with chlorine to form methyl chloride and ethyl chloride, respectively. CH4 + Cl2 → CH3Cl C2H6 + Cl2 → C2H5Cl v. All members of a homologous series can be prepared by the same general method of preparation. For example, alcohols can be prepared from alkyl halides. Significance of a Homologous Series i. Helps in the systematic study of organic compounds. ii. Predicts the properties and the nature of other elements of the series if the same is known of the first few members. Isomers Compounds with the same molecular formula but different structural formula are known as isomers, and the phenomenon is known as isomerism. Examples: Butane and isobutane are two different compounds with the same molecular formula C 4H10. Butane Isobutane Causes of Isomerism i. Difference in the mode of linking of atoms. ii. Difference in the arrangement of atoms or groups in space. Different Types of Structural Isomerism i. Chain isomerism Two or more compounds which have a similar molecular formula but different arrangement of carbon atoms in straight or branched chains are referred to as chain isomers, and the phenomenon is known as chain isomerism. ii. Position isomerism When two or more compounds with the same molecular formula differ in the position of the substituent atom or functional group on the carbon atom, they are called position isomers, and the phenomenon is known as position isomerism.  iii. Functional isomerism Two or more compounds with the same molecular formula but different functional groups are called functional isomers, and the phenomenon is known as functional isomerism. iv. Metamerism It arises because of unequal distribution of alkyl groups on either side of the functional groups in the molecules. Nomenclature It is the system of assigning names to organic compounds. The Systems of Nomenclature Are i. Trivial system ii. IUPAC (International Union of Pure and Applied Chemistry) system According to the IUPAC system, the name of an organic compound consists of three parts: i. Root word ii. Suffix iii. Prefix i. Root word It depends on the number of carbon atoms present in the longest carbon chain selected. Number of carbon atoms Root word One carbon atom C1 Meth Two carbon atoms C2 Eth Three carbon atoms C3 Prop Four carbon atoms C4 But Five carbon atoms C5 Pent Six carbon atoms C6 Hex Seven carbon atoms C7 Hept Eight carbon atoms C8 Oct Nine carbon atoms C9 Non Ten carbon atoms C10 Dec ii. Suffix The root word is followed by an appropriate suffix, which represents the nature of the bond in a carbon–carbon atom. Nature of bond Suffix General name General formula Single bond (C–C) -ane Alkane CnH2n+2 Double bond (C=C) -ene Alkene CnH2n Triple bond ( ) -yne Alkyne CnH2n−2 Group (R-) -yl Alkyl CnH2n+1 iii. Prefix It denotes the substituent, alkyl or functional group and its position in the carbon chain. Di-, tri- and tetra- are used for two, three and four groups of the same type, respectively. Functional Group It is an atom or a group of atoms which defines the structure (or the properties of a particular family) of organic compounds. Characteristics of a Functional Group i. Compounds of the same functional group are identified using the same types of tests. ii. The physical and chemical properties of the compounds of different functional groups are different. iii. There exists a homologous series of compounds containing a particular type of functional group. Functional General Organic Suffix Examples with common and IUPAC group formulae compound name Halide R–X Haloalkanes ane CH3Cl –X Common name: Methyl chloride (F, Cl, Br, I) IUPAC name: Chloromethane Hydroxyl R–OH Alcohols ol C2H5OH –OH Common name: Ethyl alcohol IUPAC name: Ethanol Aldehyde Aldehydes al CH3CHO –CHO Common name: Acetaldehyde IUPAC name: Ethanal Carboxyl Carboxylic oic CH3CH2COOH –COOH acids acid Common name: Propionic acid IUPAC name: Propanoic acid Ketones one CH3COC2H5 Common name: Diethyl ketone Keto IUPAC name: Pentanone Ethers R–O–R′ Ethers oxy CH3–O–C2H5 Common name: Ethyl methyl ether IUPAC name: Methoxy ethane Alkanes  Alkanes are hydrocarbons in which all the linkages between the carbon atoms are single covalent bonds.  Compounds are known as saturated hydrocarbons because all the four valencies of carbon are fully satisfied.  General formula : CnH2n+2  These hydrocarbons are relatively unreactive under ordinary conditions so they are also called paraffins. Isomerism in Alkanes  Alkanes with more than three carbon atoms form isomers.  The various isomers differ in the framework of the carbon chains. Example: Isomers of Pentane (C5H12) n-pentane isopropane neo-pentane Laboratory Preparation of Methane and Ethane CH3COONa + NaOH Na2CO3 + CH4 C2H5COONa + NaOH Na2CO3 + C2H6 Methods of Preparation of Methane and Ethane 1. From iodomethane or bromoethane: CH3I + 2[H] → CH4 + HI C2H5I + 2[H] → C2H6 + HI 2. Methane is produced on addition of water to aluminium carbide at room temperature. Al4C3 + 12H2O → 3CH4 + 4Al (OH)3 3. Ethane from alkyl halides: 2CH3I + 2Na CH3–CH3 + 2NaI This reaction is known as the Wurtz reaction. Chemical Properties 1. Substitution reaction (i) Reaction with halogens CH4 + Cl2 CH3Cl + HCl CH3Cl + Cl2 → CH2Cl2 + HCl CH2Cl2 + Cl2 → CHCl3 + HCl CHCl3 + Cl2 → CCl4 + HCl (Carbon tetrachloride)  (ii) Reaction with oxygen CH4 + 2O2 →CO2 + 2H2O 2C2H6 + 7O2 →4CO2 + 6H2O Insufficient supply of air 2CH4 + 3O2 →2CO + 4H2O 2C2H6 + 5O2 →4CO + 6H2O 2. Cracking or Pyrolysis 2CH4 CH CH +3H2 CH3–CH3 CH2=CH2 + H2 3. Catalytic oxidation of alkanes 2CH4 + O2 2CH3OH 2C2H6 + O2 2C2H5OH CH4 +O2 HCHO + H2O C2H6 + O2 CH3CHO + H2O 4. Slow combustion CH4 CH3OH HCHO HCOOH Alkenes  Alkenes are unsaturated aliphatic hydrocarbons containing a carbon–carbon double bond.  They are also called olefins because of their tendency to form oily products.  The general formula of alkenes is CnH2n. Structure of Ethene Electronic structure Structural formula (C2H4)  Two carbon atoms linked by a double covalent bond.  A double covalent bond is formed by sharing of two pairs of electrons between the two carbon atoms.  Four C–H single covalent bonds and one C=C double covalent bond.  It is a planar molecule and all bond angles (H–C–H and H–C=C) are of 120°. Preparation of Ethene i. Dehydration of ethyl alcohol CH2 =CH2 + H2O ii. Dehydrohalogenation of ethyl bromide + KOH CH2=CH2 + KBr + H2O (alcoholic) iii. Cracking of methane CH3–CH3 CH2=CH2 + H2 Chemical properties 1. Addition Reactions (i) Catalytic hydrogenation CH2=CH2 + H2 C2H6 (ii) Halogenation CH2=CH2 + Cl2 (1,2-dichlorethane) (iii) Reaction with Halogen Acids CH2=CH2 + HBr → (bromoethane) (iv) Reaction with Sulphuric acid CH2=CH2 + H. HSO4 → (ethyl hydrogen sulphate) (v) Ozone CH2=CH2 + O3 (ethylene ozonide)  (vi) Oxidation CH2=CH2 + H–O–H + [O] → (1,2-ethanediol) Cold alkaline KMnO4 solution C2H4 + 3O2 → 2CO2 + 2H2O + Heat (vii) Polymerisation n CH2=CH2 (polyethylene) Alkynes  Alkynes are unsaturated aliphatic hydrocarbons containing a carbon–carbon triple bond in their molecule.  The general formula of alkynes is CnH2n−2.  They are more reactive than alkenes because of the presence of a triple bond, often referred to as an acetylenic linkage. Structural formula of Ethyne Electronic structure Structural formula (CH2=CH2) Preparation of Ethyne i. Laboratory preparation from calcium carbide + 2H–OH → + Ca(OH)2 ii. From 1,2-dibromoethane + 2KOH + 2KBr + 2H2O iii. From methane 2CH4 + 3H2 Chemical Properties 1. Addition Reactions a] Catalytic Hydrogenation + H2 CH2=CH2 + H2 C2H6 b] Halogenation + Cl2 + Cl2 → c] Reaction with Halogen Acids + HBr → + HBr → d] Ozone + O3 → (acetylene ozonide) e] Oxidation of ethyne (Combustion) 2 + 5O2 → 4CO2 + 2H2O + Heat Alcohols  Alcohols are hydroxyl derivatives of alkanes obtained by replacement of one, two or three hydrogen atoms of alkanes by the corresponding number of –OH groups.  The hydroxyl group is the functional group of alcohols.  The general molecular formula of alcohols is CnH2n+1 OH. Preparation of Ethanol (i) Laboratory preparation by hydrolysis of alkyl halides C2H5Cl + NaOH (aq) C2H5OH + NaCl (ii) Industrial Method (a) Hydration of Ethene C2H4 + H2SO4 C2H5HSO4 C2H5HSO4 + H2O →C2H5OH + H2SO4 (b) Fermentation of Carbohydrates C12H22O11 + H2O C6H12O6 + C6H12O6 C6H12O6 2C2H5OH + 2CO2 Chemical properties 1. Combustion C2H5OH + 3O2 → 2CO2 + 3H2O 2. Oxidation with K2Cr2O7 C2H5OH CH3CHO CH3COOH (acetic acid) 3. Reaction with Sodium 2C2H5OH + 2Na →2C2H5ONa + H2 4. Reaction with Acetic acid C2H5OH + CH3COOH → CH3COOC2H5 + H2O 5. Reaction with Sulphuric acid C2H5OH CH2=CH2 + H2O 2C2H5OH C2H5 –O – C2H5 + H2O 6. Reaction with PCl3 3C2H5OH + PCl3 → 3C2H5Cl + H3PO3 Carboxylic Acids  Carboxylic acids are organic compounds containing a carboxylic group (–COOH) attached to an alkyl group or to a hydrogen atom.  Representation of carboxylic acids: R-COOH (R is either –H or alkyl)  The functional group of carboxylic acids: –COOH (carboxylic)  The acidic character in carboxylic acids is because of the presence of the replaceable hydrogen atom in the carboxylic group. Preparation of Acetic Acid A] By oxidation of ethyl alcohol C2H5OH + [O] CH3CHO + H2O CH3CHO+ [O] CH3COOH B] By hydrolysis of ethyl acetate CH3COOC2H5 + H2O CH3COOH + C2H5OH Chemical Properties 1. It is a weak acid and turns blue litmus red. 2. Reaction with Alkalis CH3COOH + NaOH → CH3COONa + H2O CH3COOH + NH4OH → CH3COONH4 + H2O 3. Reaction with Carbonates 2CH3COOH + Na2CO3 →2CH3COONa + H2O + CO2 CH3COOH + NaHCO3→CH3COONa + H2O + CO2 4. Reaction with Alcohols CH3COOH + C2H5OH CH3COOC2H5 + H2O 5. Reaction with PCl3 CH3COOH + PCl5 → CH3COCl + POCl3 + HCl 6. Reduction CH3COOH + 4[H] →C2H5OH + H2O