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ORGANIC CHEMISTRY—AN INTRODUCTION es ec c (© s\ V ) ri nds, whose source was related pound: ose source! ( ys i 1c y, devoted to the study of ca bon comfy , i ife). Essenti all the chemical reactions the living system, was termed as organic chemistry (organic means life). Essentially, a i i This is becaus: es of life such as proteins, that take place in the living system are organie reactions. This is because the molecul P Ae f iio vitamins, lipids, carbohydrates, chlorophyll, haemoglobin, nucleic acids, and so on contain carbon. In fact, ou! © for food i coll and silk ic) tural gas and petroleum) is, dependent) ature for 1, clothing (¢ wool, and silk) and energy (natural gas and p' ) pen 4 oe 4 F any asically, the di ney on organic compounds. Thus, the simplest definition of organic chemistry is the st f i : is y carbon, of compounds that contain carbon, the study of compounds where carbon is covalently bonded to cu hydrogen, halogens, oxygen, nitrogen and sulfur. ELEMENTAL ANALYSIS Elemental analysis is a technique used in chemistry to determine the elemental composition of a sample. Elemental analysis is a crucial step in identifying and characterizing chemical compounds, it involves determining the percentage of each element present in a sample Types of Elemental Analysis il, Qualitative analysis: Identifies the elements present in a sample 2 Quantitative analysis: Determines the percentage of each element present in a sample Methods of Elemental Analysis 1. Gravimetric analysis: Measures the mass of an element or compound to determine its percentage in the sample i) Titration: Uses a reaction with a known volume of a reagent to determine the amount of an element or compound 3. Spectroscopy: Uses the interaction between matter and electromagnetic radiation to determine the elemental composition 4. Atomic Absorption Spectroscopy (AAS): Uses the absorption of light by free atoms ina sample to analyze the presence and concentration of specific element. Applications of Elemental Analysis 1. Pharmaceuticals: To determine the purity and composition of drugs 2. Environmental monitoring: To analyze water and air samples for pollutants 3. Food safety: To detect and quantify contaminants in food 4, Materials science: To characterize the composition of materials Page 2 of 16 Solution, The empirical formula is calculated as follows: we a be y 2 % Of Or The percentage of C + H = 40 + 6.7 = 46.7% and as the rest is oxygels the % Simplest whole of each Element % | “Atomic mass | Bee ee mass number ratio | if 33/3.33 = 1 Cc Hite] 12 402 = 3,33 a 33 «2 H 67 { 6.7/1 = 6.7 aa LA o 533 | 16 63.3/16 = 333 eee Hence the empirical formula is CH20. The empirical formula mass = 12 + 2 + 16 = 30. The molecular mass = Vapour density x 2 =30x2=60 The molecular formula = [Empirical formula] where, 7 = molecular mass/empirical mass = 60/30 =2 Hence, molecular formula = [CH2O]2 = C2H4O>. Once molecular formula of a compound is known, its structure can be determined by various chemical and physical methods. CLASSIFICATION OF ORGANIC COMPOUNDS (HYDROCARBON) Organic compounds based on certain characteristics are classified into the following categories, Acyclic (Aliphatic) Saturated Unsaturated Hverayctc] Saturated Unsaturated Page 4 of 16 Acyclic Compound: Is one of a group of organic compounds of carbon (C) and hydrogen (H) in which the carbon atoms have linear, branched chain (open), or both types of structures, Aliphatics, as they are informally called, can be divided into paraffinic (saturated) and olefinic (unsaturated) chain types. The simplest paraffinic aliphatic is methane, CHa. The simplest olefinic aliphatic is ethylene, C2Ho Cyelic Compound Closed: Any one of a class of compounds whose molecules contain a number of atoms bonded together to form a closed chain or ring. Cyelie compounds are also known as “Ring compounds”. As its second name suggests, cyclic compounds are those kinds of compounds where one or more than one number of atoms get connected to form a closed ring. It is not mandatory that every ring of these compounds is to be of the same [> LJ cyclopropane cyclobutane size, cyclopentane fa cyclohexane cyclohexane cyclooctane 1, Alkane is a hydrocarbon that has only single bonds. Alkanes has a general formula of C,H2,+> 2. Alkene is a compound that has at least one double bond. Alkene general formula is C,H2». 3. Alkyne is a compound that has at least one triple bond, Alkyne general formula C,,H2, IUPAC NOMENCLATURE The IUPAC name of any organic compound essentially consists of three parts which can be described as follows, 41, Stem name: It is the basic unit of the systematic name which describes the carbon skeleton. It is also referred as the ‘word root’ 2. Prefix: The stem name may have certain groups or atoms attached to it which are termed substituents 3. Suffix: A suffix denotes the functional group present in a compound and is always added after the stem name (word root) Page 5 of 16 al S Thedifferent s ‘ 5. The different alkyl groups, present in a compound, are written in an alphabetical order, irrespective of their position in the carbon chain CH, CHy=CH, | | a Ethyl is written first due to CHy CH y alphabetical proterence over 1° 9 t—CH Ch, one mothyl lirespoctivo of ordor of V-Ethyl-2-Methylpentane — @7e Nerpgation (Noo) 2-meyt-s.cthyipemtane 6. If two or more similar alkyl groups are present in. a compound, the words di, tri, tetra, and so on are used to specify the number of times these alkyl groups appear in the chain, However, these prefixes themselves are not considered for writing the alphabetical order. For example, CH, CHy CH{CH, ew d L i CH Gh — Crean, CH,—CH—CH—CH—CH,— CH, 1 2 3 A. n 2 3 4 ce 6 Ethyl is written first CH, CH due to alphabetical - preference over 2,3-Dimethylpentane 4-Ethyl-2,3-dimethylbexane methyl as —_——— ‘a}- ®&) 2,3-dimethyl-4-ethylhexane Is not considered in alphabetical order 7. If two different alkyl groups are present at an equal distance from either end of selected chain, the alkyl group which comes first in the alphabetical order gets the lowest possible rank. For example, CH, Ethyl and methyt groups Oy BO). ey Oe) (screened) are present al CH,—CH,—CH —CH—CH,—CH, equal distance from either 1 BUNA SD id) Sunk 6 end of the present chu CH3CH, ' 3-Ethyl-4-met In such case, alphal SS eat for the substituents ( @) 4-Ethy|-3-methythexane methyl) is taken into consideration 4 for numbering. 8. If more than two alkyl groups are present and branching occurs at an equal distance from either end, the numbering is done from the end which gives minimum possible number to all the substituents. For example, CH, CH, © @'*® ® Oo All the three CH, =CH—CH—CH,—CH—CH, methyl groups —— ! 2 3 + S 6 (locant) get the CH, lowest ib! Ruratarina4 ” 2.3,5-Trimethythexane a ae (Mod) 2.4.5-timetnythnexane 9. If the substituent is a branched chain alkyl group then it is numbered separately. The numbering of the branched substituent starts from the point of attachment to parent chain, The branched chain alkyl group is always written in a bracket as a prefix. Page 7 of 16 Branched side chain numbered a eile 5 separately and numbering sans — S Chi, —CH—CH,—CH. from the point of attachment to CHy § HCH Gis Parent chain and here it is 4 H,—C 1-methylpropyl CH—CH,—C bic) che aye 7 5-(|-methylpropy!) nonane CH,—CH,—CH,—CH,— 1 2 3 4 The Shape of Ethane (Alkane) Ethane (C2Hs) is a molecule with a tetrahedral shape. The two carbon atoms are at the center of the tetrahedron, with the six hydrogen atoms at the corners. The bond angle between the carbon-hydrogen bonds is approximately 109.5 degrees. This shape is a result of the sp? hybridization of the carbon atoms, which leads to a stable and symmetrical molecular structure. K y Oy aa a ALKENES: The basic rules for naming alkenes are similar to those for alkanes but include the indication for position of double bonds. Additional rules pertaining to alkenes can be summarized as follows: 1. The longest possible continuous carbon chain should include the carbons of double bond. 2. The longest chain is given the name by replacing suffix -ane (in case of alkanes) with -ene. 3. The numbering is done in such a way that first carbon of double bond gets the lowest number. 4. The carbon atoms of the double bond get the preference over the other substituents present in the parent chain. 5. Inanalkene, the position of double bond is indicated by placing the number before the suffix —ene ia ze 1 4 3 2 1 1 2 3. 4 H,C=CH, H,C—CH=CH, CH,—CH,—CH=CH, CH,—CH=CH—CH, But-l-ene Bul-2-ene Ethene Propene [1-Butene]* [2-Butene|* *Refer Notabilia 3, 3-Ethyl-4-methylpent-l-ene 6. If more than one double bond is present, the location of each double bond is indicated just before the suffix. The suffix used, for two double bonds is - diene, for three double bonds it is -triene, and so on. The general name for dienes is “A/kadiene’. 1 2 3 4 3 3 4 a H,C=CH—CH=CH—CH, He CH Ch, —CH—CH) Penta-1.4-diene it a 3 Penta-!,3-diene Page 8 of 16 seid. is a planar, regular hexagon. The molecule has a symmetrical, flat structure with: a) 6 carbon atoms arranged ima hexagonal ring b) 6 hydrogen atoms, one attached to each carbon atom c) Bond angles of 120 degrees between adjacent carbon atoms 4) Delocalization of electrons in the ring, resulting in equal bond lengths and a planar shape This unique shape is due to the resonance stabilization of the molecule, which allows the electrons to delocalize and the molecule to adopt a planar, symmetrical structure. ALKYL HALIDES (RX) 1. Halogens are always treated as substituents and while naming, written as prefix to the name of a compound. 2. The IUPAC name for alkyl halides is Haloalkane. CHCl, Trichloromethane ‘ CH CHCl CH,Br 5 Bromcsnethané! (Common nowie: Chloroform) Fluoromethane — Chloromethane 3. The carbon having halogen is given the lowest possible numbering. CH;CH.Cl —CHCH,CH.Br CH,CHCH, Chloroethane 1-Bromopropane ! 2lodopropane Br | CH,—CHBr, —_BrCH,CH,Br Br—CH,—CH—CH,—Br 1.2,3-Tribromopropane present at an equal distance from either end then numbering is done according to 1 2 3 BrCH,—CH—CH,—I (OC) EO) CH; |-Bromo-3-iodo-2-methylpropane 3-Bromo- 1 -iodo-2-methylpropane Page 10 of 16 SOMENISM ~ fsomers are molecules with the same molecular formula but different structures of arrangements of ators. Types af omeriom a, Structural lsomerism (or Constitutional leomeriorn) Z Stereosomeriom (or Spatial leomeriom) Structural leomerism tor Consthuttonal Ivomeriom): Vors wowmers have same molecular formula but different bond connections between atoms. Structural Isomeriomn is further classified into the following: 4) Chain Inomerism: Different length or branching of carbon chain have molecular formula Cayo but they differ in their carbon skeleton, for example, butane and 2-methylpropane CHLU CHEK, oie CH, Fev Leming res b) Povition Isomerism: Different position of functional group or substituent. For example CHBHEEH, CHCHCH, CHLH LH LH, CH .CHCHCH, . j j On On & Br Fuga bl Kegan tA ireneanneace 2 Breenakaaeer Veriion werner $0 CN LD Yonicam wenears tea C Afr ¢) Functional {somerism: different functional group. For example Kumtumal womens CA, CH, ON CH,—-O—CH, for MO Te ) Functional tomers = CH,CH,—CH cH,—C—CH, | tH CMO i fl oO oO Propretas Propane | Stercoisomerism (or Spatial Isomerism): Same bond connections, but different arrangement in space a) Enantiomers: They non-superimpovable mirror images, optically active and rotate plane-polarized light in opposite directions. Examples: L- and D-Lactic acids. COOH COOH J { | H-C~OH OH-C-H | | CHs CH: d-lactic asi {lactic acid Lt INDUCTIVE EFFECT AD Definition; The inductive effect is the ability of a substituent to withdraw or donate electron density to a molecule through a sigma (o) bond. Types of Inductive Effect: 1, The atoms or groups which are more electronegative than carbon withdraw electrons from carbon and are said to exhibit -I effect (minus I effect), For example, F, Cl, Br, 1, -OH, -NO: and so on 2. The atoms or groups more electropositive (less electronegative) compared to carbon release electrons towards carbon and are said to exhibit +I effect (plus | effect), For example, Li, Na, K, alkyl group and so on. The hydrocarbons contain carbon and hydrogen atoms and are thus non-polar in nature as there 1s not much difference in the electronegativity of carbon and hydrogen. For example, in alkanes carbon ~ carbon and carbon —hydrogen o bonds are present. If we replace hydrogen by an atom like fluorine, which is more electronegative than carbon, fluorine will carry a negative charge, as it will attract shared electrons towards itself and thus, the carbon skeleton will carry positive charge. This carbon, in turn, induces a small positive charge on the adjacent carbon. Similarly, when hydrogen 1s replaced by an atom such as lithium which is more electropositive than carbon, the lithium will carry a positive charge. Now, carbon being more electronegative attracts the shared electrons towards itself and will carry a negative charge. This induces a small negative charge on adjacent carbon. Pa Sa —C—C—C+> C++ C+F -leffect g8b- B- 5- be CHC CHE CEH LI— sHeoct ‘As the attachment of the number of groups, exhibiting either +1 or -I effect, on a carbon increases it experiences the corresponding inductive effect to a greater extent. For example. CHy CHy H H t t | | CH, + C— CH,+C— CH,+C— H-C— 4 I i | CH; H " u Increasing 41 eflect on earhon with increasing number of CH, groups ca ca H H ¢ t | ci-C— Cro Chait Hea a H H H tnwasing -Teffect on earhoo wit increasing number of chlorine atoms The characteristic features of inductive effect include a) It is a permanent effect. b) This effect operates through @ bonds. Page 13 of 16 in and ceases to operate beyond ©) is observed for a maximum of up to second carbon atom of the chain fourth carbon, RESONANCE ies and reactivity of The Lewis structure of a molecule or ion can be used for predicting the structural properties an F Ss. that molecule, A number of molecules or ions can be represented by more than one correct ee i? ; For example, let us write the different resonance forms for formate ion and discuss their relative contribution. 2 oO H— w (1) Structure [I] and [II] are equivalent and contribute equally, however in structure [III] the number of covalent bonds is three (less than {IJ and [II] which have four). Also, structure [III] has an electron deficient carbon with Positive charge and thus it is least contributing. Delocalization of electrons during resonance is shown to occur in three ways: 1. Shifting of electrons from 7 bond to adjacent bond. In the following examples the shaded portion indicates the shifting of electrons from 7 bond to adjacent bond. CHS cnktu, es ¢n,—cH=cH—Cn, oe oO | on, Lomen, Ch, —cH=cH, 2. Shifting of electrons from 7 bond to an immediately next placed atom. CH. Lamcnktn — CH.—cH=cH—th, ¥ 7 R= (—g Rc < No The groups containing bonds such as oO (o) +0 | N ‘i CEN, Li, ‘CR, The groups directly attached (0 q benzene ring through an atom 4 which is further attached to a more oon electronegative atom through am bond, exhibit -R effect. and so on when attached directly to benzene ring withdraw electrons from ring by participation in delocalization through mn overlap. Examples: Nitrobenzene (CsHsNO:): nitrogen delocalizes electron density, withdrawing from the ring “Key Note: Inductive Effect Resonance Effect 1. Inductive effect operates through o bonds 2. Inductive effect is a local effect 1. Resonance effect operates through x bonds 2. Resonance effect is a delocalized effect Both effects can influence the reactivity and physical properties of a molecule Page 16 of 16 
