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Unit 09 ‐ ORGANIC CHEMISTRY Scope of Organic Chemistry Introduction:‐ Observation of our surroundings show wide variety of living structures, delicious food items, vibrant coloured clothes, innumerable automobiles, range of health fitness medicines etc. “The essence of all these is the element Carbon”. It is wonderful to understand the form of carbon in all of the above. Special properties:‐ Carbon has four electrons in the outermost orbit (tetravalent). Carbon shares four valence electrons with other atom of carbon or with atoms of other elements to form four covalent bonds in order to attain octet form. Carbon also exhibits unique catenation property, by which carbon atoms are linked through a covalent bond to form various kinds of chain of carbon atoms. With the advantage of tetravalency and catenation, carbon forms large number of compounds such that, the number of compounds formed by carbon alone, exceeds number of compounds formed by all the other elements in the periodic table. Definition :‐ Organic chemistry is “chemistry of compounds of carbon”. It is these compounds of carbon in various forms that constitute all aspects of our life. Applications :‐ 1. Food which comprises of carbohydrates (Glucose, sucrose, fructose etc), proteins (amino acids), oils and fats (Glycerides) are carbon compounds. 2. Clothes and fabrics made of cotton (cellulose), silk (wood pulp), Nylon (from adipic acid and dimethyl amine), terylene (from dimethyl terphthalate and ethylene glycol), acrylic (artificial wool) comprise of carbon in different form. 3. Clothes are colourful due to dyes (colouring matter) which are yet again carbon compounds Alizarin dye imparts red colour, indigo‐blue, malachite – green, Naphthol‐yellow. 4. Various hydrocarbons like petrol, diesel, kerosene gasoline are energy sources to run engines in automobiles. 5. Propellants, a kind of fuel used in rocket is a mixture of fuel and an oxidizer. 2
6. Application of organic compounds in usage of drugs in the field of medicine has given rise to chemotherapy. To name a few, dettol (Chloro‐xylenol), salol are antiseptics, penicillin, tetracycline are antibiotics, aspirin, despirin, novalgin which reduce pain are analgesic, paracetamol, crocin used during fever are antipyretic, antimalarial drugs like chloroquin, quinine are used to cure malaria. 7. Petrochemicals are used as raw materials in the manufacture of polymers, detergents, pesticides and even in cosmetics. 8. Living protoplasm structures essentially found in animals and plants is made up of carbon. The carbon left behind after death or decay of living structures and matter is an evidence to ultimate role of carbon in everything. Functional Group:‐ Structural feature of carbon compound show carbon bonding with hydrogen invariably and some time with hetero atom (different atom) like halogen, oxygen, nitrogen, sulphur and phosphorous. Presence of hetero atom or group with heteroatom, in the structure of carbon compounds confer specific properties to the compound, hence are called functional groups. Thus functional group is defined as an atom or group of atoms that determines the characteristic properties of organic compounds. Examples :‐ Structure Compound Functional group H Methyl alcohol ‐OH : alcohol H – C – O – H H H O H – C – C – O – H H Acetic acid ‐ COOH: Carboxylic acid Acetaldehyde ‐ CHO; aldehyde Methylchloride ‐ Cl : chloro H H H – C – C = O H H H – C – C l H 3
Homologous series:‐ Homologous series is the series of closely related compounds with similar chemical properties. Characteristics:‐ 1.
2.
3.
4.
These series are represented by General formula Two successive member of series differ by ‐CH2. They are prepared by common methods Show a regular gradation in physical properties. Example: Homologous series alkane has general formula CnH2n +2 and that of alkene and alkyne, CnH2n and CnH2n‐2 respectively where n is number of carbon atoms. Alkane series Name Molecular Formula Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Alkene series Name Ethene Propene Butene Pentene Molecular Formula C2H4 C3H6 C4H8 C5H10 Alcohol series Name Methanol Ethano Propanol Butanol Molecular Formula CH3OH C2H5OH C3H7OH C4H9OH 4
Emperical formula and Molecular formula: Compounds are represented by a chemical formula and is of two types a) empirical formula b) molecular formula Emperical formula gives the simple whole number ratio of atoms of various elements present in one molecule of the compound. Example: Hydrogen peroxide has empirical formula HO, hydrogen and oxygen are in the ratio of 1 : 1. Glucose has empirical formula CH2O, carbon, hydrogen and oxygen are present in the ratio of 1:2 : 1. Molecular formula gives the actual number of atoms of various elements present in one molecule of the compound. Example: Molecular formula of benzene is C6H6 which show 6 atoms of carbon and 6 atoms of hydrogen. Compound Emperical formula Molecular formula Hydrogen peroxide HO H2O2 Glucose CH2O C6 H12 O6 Benzene CH C6 H6 Napthalene C5H4 C10 H8 Ethene CH2 C2H4 Ethane CH3 C2H6 Relation between emperical formula and molecular formula : Emperical formula and molecular formula are related by Molecular formula = ( emperical formula )n Where n is simple whole number and is given by, Molecular mass n = Emperical formula mass Example : Molecular mass of acetylene is 26, Emperical formula of acetylene is CH, ∴emperical formula mass is 13. 26
∴n = = 2 13
∴molecular formula of acetylene = (CH)2 = C2H2 5
Hydrocarbons :‐ Hydrocarbons are compounds made up of carbon and hydrogen. Hydrocarbons are regarded as chief or parent compounds, hence modern definition of organic chemistry is, “the chemistry of the hydrocarbons and their derivatives”. Other compounds of carbon are considered as derivatives of hydrocarbons that are obtained by replacing one or more hydrogen atoms with atoms of elements like oxygen nitrogen, halogen etc. Classification:‐ Hydrocarbons are classified as 1. Saturated hydrocarbons 2. Unsaturated hydrocarbons Saturated hydrocarbons contain carbon‐carbon single bond. Example: alkanes, cycloalkanes. Unsaturated hydrocarbon contain carbon‐carbon double bond or carbon‐carbon triple bond or both. Example: alkenes, alkynes Alkanes are compounds containing different carbon atoms with carbon‐carbon single bond to form open chain of carbon atoms. Example: methane, ethane, etc. Alkenes are compounds containing carbon‐carbon double bond in the open chain of carbon atoms. Example: ethene, propene, etc. Alkynes are compounds containing carbon – carbon triple bond in the open chain of carbon atoms are termed as alkynes. Example: ethyne, propyne, etc. Structural representation of hydrocarbons:‐ Structural formula is represented by showing, covalent bond by ”—” between two atoms. Hence, single bond is represented by ”—”, double bond is represented by “=”, triple bond is represented by “≡”. Since carbon is tetravalent, in the structural formula, always carbon has four bonds. 6
Examples:‐ 1. Alkanes Name Methane Molecular formula CH4 Structural formula Ethane C2H6 H H
H – C – C – H H H Propane C3H8 H H H
H – C – C – C – H H H H 2. Alkenes Ethene C2 H4 H H
H – C = C – H H
H – C – H H H H H
H – C – C = C – H H H H H H H – C = C – C ‐ C – H H H Propene C3 H6 Butene C4 H8 3. Alkynes Ethyne C2 H2 H – C ≡ C – H Propyne C3 H4 Butyne C4 H6 H
H – C – C ≡ C – H H H H H – C ≡ C – C – C – H H H Substitution reaction : Reactions in which one or more hydrogen atoms of hydrocarbons are substituted or replaced by some other atom or group of atoms. Example: Halogenation of alkanes ‐ It involves replacement of hydrogen atoms of alkane by halogen atom. Chlorination : Methane when treated with chlorine in presence of diffused light forms chloromethane, dichloromethane, trichloromethane, tetrachloromethane by replacing one, two, three and four hydrogen atoms of methane. 7
CH4 + Cl2 diffused‐light CH3Cl + HCl (methane) (chloromethane) CH3Cl+ Cl2 diffused‐light CH2Cl2 + HCl (dichloromethane) CH2Cl2 + Cl2 diffused‐light CH Cl3 + HCl (trichloromethane or chloroform) CH Cl3 + Cl2 diffused‐light CCl4 + HCl (tetrachloromethane or carbon tetrachloride) Addition Reactions: Alkenes and alkynes contain double and triple bonds respectively and are rich source of electrons. Hence are more reactive and undergo addition reactions to form saturated products. Example:‐ 1. Addition of hydrogen: Ethene undergo addition reaction with hydrogen, when heated in presence of nickel catalyst to form ethane H H H H H – C = C – H + H2 Ni H – C – C – H ethene ∆ H H ethane 2. Addition of bromine: Ethene undergo addition reaction with bromine in carbon tetrachloride to form 1, 2 di bromo ethane. H H H H H – C = C – H + Br2 CCl4 H – C2 – C1 – H ethene Br Br 1, 2 – dibromoethane Nomenclature (Elementary idea):‐ IUPAC system of naming organic compounds A proper name is assigned to a particular organic compound on the basis of IUPAC system (international union of pure and applied chemistry) In IUPAC system, name of organic compound consists of three parts 1) root word 2) suffix 3) prefix. 8
1. Root word denotes number of carbon atoms in the parent chain. Root word for carbon chain containing different number of carbon atoms are as given below. No. of carbon Root No. of carbon Root word atoms in chain word atoms in chain 1 meth 6 hex 2 eth 7 3 prop 8 oct 4 but non 5 pent 10 9 hept dec 2. Suffix : It is the word linked to the root word at the end. It is of two types a) primary suffix: It indicates nature of linkage in carbon atoms. Example: For carbon atoms linked by a single covalent bond, suffix: ane, for carbon atoms linked by double bond, suffix: ene, for carbon atoms linked by triple bond, suffix: yne. b) Secondary suffix indicates presence of functional group and secondary suffix word is added by replacing ‘e’ of ane, ene and yne of primary suffix word. (Note: ‘e’ is retained if secondary suffix begins with a consonant ) Class of organic Functional group Secondary Suffix compound Alcohols ‐ OH ‐ ol Aldehydes ‐ CHO ‐ al Ketones ‐ C = O ‐ one Carboxylic acids ‐ COOH ‐ oic acid Esters ‐ COOR ‐ alkyl……..oate Nitriles ‐ C ≡ N ‐ nitrile Amines ‐ NH2 ‐ amine 9
3. Prefix : It refers to side chain or substituent and is placed before the root word. Substituent Prefix Substituent Prefix ‐ F Fluoro ‐ No nitroso ‐ Cl Chloro ‐ OCH3 methoxy ‐ Br Bromo ‐ OC2H5 ethoxy ‐ I Iodo CH3 ‐ Methyl ‐ NO2 Nitro CH3CH2 ‐ Ethyl Hence IUPAC names of some alkane, alkene and alkynes are as follows. Common name Compound Root word IUPAC name H Root word : meth Meth + ane = methane 1) Methane H – C – H Primary suffix: ane H H H 2) Ethane Root word : eth Eth + ane = ethane H – C – C – H Primary Suffix : ane H H H H H 3) Propane Root word : prop Prop + ane = propane H – C – C – C – H Primary Suffix : ane H H H H H 4) Ethylene Root word : eth eth + ene = ethene H – C = C – H Primary Suffix : ene H H H 5) Propylene Root word : prop Prop + ene = propene H – C – C = C – H Primary Suffix : ene H but + ene = but – 1 – ene Root word : but 6) α‐butylene H H H H H – C1 = C2 – C3 – C4 – H Primary Suffix : ene H H (double bond at 1st carbon) H – C ≡ C – H 7) Acetylene Root word : eth eth + yne = ethyne Primary Suffix : yne 8) Methylacetylene H H – C – C ≡ C – H H 9)Ethylacetylene H H H – C4 –C3 – C2 ≡ C1 H H H Root word : prop Primary Suffix : yne Root word : but Primary Suffix : yne Prop + yne = propyne but + yne = but – 1 – yne 10
IUPAC names of compounds with Functional groups Common Name Compound Alcohols :‐ H H
1) Ethyl alcohol H – C – C – OH H H IUPAC name Ethanol 2)n‐butyl alcohol Aldehydes:‐ 3) Formaldehyde H H H H
H – C – C – C – C – O ‐ H H H H H H H – C = O Butanol Methanal 4) Acetaldehyde Ketones:‐ 5) Dimethyl ketone H H
H – C – C = O H O H
H – C – C – C – H H H Ethanal Propanone 6) ethyl methyl ketone Carboxylic acids:‐ 7) Formic acid 8) Acetic acid H O H H
H – C – C – C – C – H H H H O H – C – O – H H O H – C – C – O – H H Butan –2–one Methanoic acid Ethanoic acid Esters:‐ 9) Ethylacetate H O H H
H – C – C – O ‐ C – C – H H H H Ethylethanoate 10) Methyl acetate H O H H – C – C – O ‐ C – H H H Methylethanoate Nitriles:‐ 11) Methyl cyanide H H – C – C ≡N H Ethane nitrile 11
H H H – C – C – C ≡ N H H 12) Ethylcyanide Propanenitrile Amines:‐ 13) Methyl amine H H H – C – N – H H Methanamine H H H
H – C – C – N – H H H 14) Ethylamine Ethanamine IUPAC names of compounds with substituent. Common Name Compound H H H
1) Isobutane IUPAC name 2‐ methylpropane 2) Ethylchloride Chloro ethane H – C1 – C2 – C3 – H H H H – C – H H H H H – C – C – C l H H 3) Isopropyl iodide H H H
H – C1 – C2 – C3 – H H I H 2 – iodopropane 4) Sec‐ butyl bromide H H H H
H – C – C – C – C – H H Br H H 2‐ bromobutane 5) Ethylmethylether H H H
H – C – O – C – C – H H H H Note:‐ Nomenclature is dealt in detail in 11th standard. Methoxyethane 12
EXERCISES 1) Explain tetravalency of carbon 2) What is catenation? 3) Carbon forms large number of compounds. Justify. 4) Define organic chemistry 5) Explain the scope of organic chemistry 6) What are functional groups? 7) Mention the functional group of alcohol and aldehye. 8) What is homologous series? Explain with example. 9) Write molecular formula of two successive homologues of C3H8 10) What is general formula of alkynes 11) What is empirical formula? Give example. 12) What is molecular formula? Give example. 13) Write the relation between empirical formula mass and molecular formula mass 14) What are hydrocarbons? 15) Classify the following in to saturated and unsaturated hydrocarbons a. Ethane c. Ethene b. Butane d. Propye 16) What are alkanes? Give example. 17) What are akenes? Give two examples 18) What are the compounds containing carbon‐carbon triple bond in the open chain of carbon atoms called as? 19) Write the structural formula of a. propane b. Butene c. Ethyne 20) What is substitution reaction? Explain chlorination of methane 21) How many substitution products are formed from the reaction between ethane and chlorine 22) Why are alkene and akynes more reactive compared to alkanes 23) Explain addition of hydrogen to ethene 24) Write the name and structural formula of product formed by addition of bromine to ethene 25) What does the root word of IUPAC name of organic compound indicate? 13
26) What is the root word given for the chain of six carbon atoms? 27) What is a primary suffix 28) What is the primary suffix given for carbon atoms linked by a. Double bond b. Triple bond 29) What is significance of secondary suffix in the nomenclature of organic compounds? 30) What are the secondary suffix for the functional groups a. Aldehyde b. Ketone c. Carboxylic acid 31) What does the prefix part of the IUPAC name of organic compounds represent? 32) What are the prefixes used for a. –NO2 b. –CH3 33) Write the structural formula for the following a. Propene b. 1‐butanol c. Chloroethane 34) Write the IUPAC name of the following a. b. H O H H H
H – C – C – O – H H – C – C – C – H H H I H **************** Prepared by : Shobha Gorbal Head of the Dept. of Chemistry, Vidya Mandir Independent PU College, 11th Cross, Malleshwaram, Bangalore