HYDROCARBON - Lecture Notes

Brilliant STUDY CENTRE CHEMISTRY -2023 Hg2+ C CH Hg2+ C CH Hg2+ C CH2 Hg2+ CH CH + H2O OH O H+ O HH C CH2 C CH2 Hg2+ OH OH CH3 C H O CH3 C CH dil.H2SO4 CH3 C CHHg CH3 C CH2Mg CH3 C CH3 HgSO4 O O C CH3 OH O CH3 CH2 CC CH3   dil.H2SO4 CH3 CH2 CH2 HgSO4 ADDITION OF ACETIC ACID CH2 CH2 COOCCH3 CH2 CH CH CH + CH3COOH OOCH3 n CH2 CH OOCCH3 n ADDITION OF ALCOHOL CH  CH  C2H5OH  CH2  CH  O  C2H5 H /H2O CH3 O C H + C2H5O11 51

Brilliant STUDY CENTRE CHEMISTRY -2023 H CH2 CH O C2H5 H+ CH2 CH O C2H5 H2O CH2 CH OH CH2 CH3 CH3 CH2 CH3 C H H O O H CH3 CH2 OH NUCLEOPHILIC ADDITION REACTION Due to the presence of sp hybridised carbon alkynes can show nucleophilic addition reaction. CH CH CH3O- CH CH OCH3 CH2 CH OCH3 CH3OH Nu + R C C R Nu C R H Nu Nu H C Nu C C R R R HYDROBORATION OXIDATION CH3 C CH H -BH2 CH3 CH C BH2 CH3 C CH CH3 CH C 2 BH CH3 C CH O 3C H 3  C H 2  C H   3C H 3  C H  C H  O H  H 2O 2 ( C H 3  C H  C )3 B aq.O H To avoid the multiple addition of alkene bulky borones like dissamyl borane (1, 2 dimethyl propyl borane) is used CH3 C CH R2BH CH3 CH CH BR2 Sia2BH 52

Brilliant STUDY CENTRE CHEMISTRY -2023 Where R CH3 CH CH BH CH3 CH3 disiamyl CH3 CH2 C C CH3 CH3 CH2 CH2 C CH3 O HYDROBORATION ALKYLATION CH3  CH2  CH2 3 B 3RCOOH CH3  CH2  CH3 CH3  CH  CH 3 B 3RCOOH CH3  CH  CH2 ADDITION OF HYDROGEN CYNADE CH CH + HCN CH2 CH CN nCH2 CH Poly CH2 CH CN CN n PAN OXIDATION REACTION 1. Complete oxidation 2CH CH + 5O2 4CO2 + 2H2O When acetylenes are burnt with air/oxygen under higher pressure they burn to form CO2 and H2O atoms with blue flame having higher temperature around 3000°C and this flame is used for cutting and welding metals. 2. Oxidation using dilute KMnO4  CH  C  OH O RC   R  C  O OO CH CH dil.KMnO4 OH C C OH 53

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 C CH CH3 C COOH O CH3 C C CH3 CH3 C C CH3 OO 3. Oxidation using acidified alkaline/KMnO4/K2Cr2O7  CH  CO2  H2O RC  RCOOH CH  CH  2CO2  2H2O CH3  C  CH  CH3COOH  CO2  H2O CH3  C  C  CH3  2CH3COOH OZONOLYSIS CH CH + O3 O HCC H CH CH Zn-H2O OO OO Glyoxal CH3 C CH CH3 O Zn-H2O CH3 C CH C CH OO OO POLYMERISATION REACTION 1. Linear polymerisation 2CH  CH NH4OCHl/CuCl CH2  CH  C  CH CHCH CH2  CH  C  C  CH  CH2 CYCLIC POLYMERISATION CH CH CH CH 3CH  CH HRoetdFe Tube CH CH 54

Brilliant STUDY CENTRE CHEMISTRY -2023 CH CH CH CH CH CH CH3 CH CH3 CC 3CH3  C  CH FeR.T.Hub. e CH CH C CH3 4CH  CH NiCDN4 CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH ISOMERISATION CH3  C  C  CH3 NaNH2  CH3  CH2  C  CH CH3  CH 2  C  CH alc.KOH CH3  C  C  CH3  BENZENES • C6H6 • Less than 8H corresponding paraffins • Highly unsaturated system • 8 observations that suggest benzene 1. Benzene and 3 molecules of H on presence of Rency Ni and cyclohexane C6H6  3H2 Rency Ni C6H12 2. Benzene add 3 molecule of chlorine and form benzene hexachloride C6H6  3Cl2 h C6H6Cl6 3. Benzene add 3 molecules of oxone and form benzene triozonide 55

Brilliant STUDY CENTRE CHEMISTRY -2023 C6H6  3O3  C6H6  O3  3 Two observations that suggest benzene shows saturated properties. 1. Benzene resist  KMnO4 oxidation like alkane 2. Benzene does not decolourise Br2 in CCl4 but benzene give monosubstitution product with bromine in presence of FeBr3 C6H6  Br2 FeBr3 C6H5  Br  HBr In 1865 Fredrich Augast Kekule suggest structure of benzene based on his dream According to Kekule, benzene containing 6C atom join each of alternatively single and double bond and each C atom goin with hydrogen. H H C C H C CC HC H H Objection against Kekule structure 1. Kekule cannot explain benzene stability against KMnO4 oxidation 2. Kekule structure explained two type of bond ie single and double bond. But X-ray diffraction shows that benzene have only 1 bond length (ie) 139 pm and is b/w C=C and C–C. 3. Kekule only explained the monosubstitution product but in case of disubstitution product there is two possibilities. Br Br Br Br (1) (2) • There is a double bond between C contaiing two Br • There is a single bond between C carrying Br If Kekule’s structure was correct there structures exist with two different properties but only one desubstitution product are known. Kekule suggest and equilibrium between there two structures and the position of single and double bond is not fixed THE STRUCTURE OF BENZENE IS EXPLAINED BY USING 1) MOT 2) Resonance theory In benzene each C atom form two C–C  bond with neighbouring two C so there is total 6 C–C  bond. Each carbon atom forms  bond with H so there is total 6CH  bond. The C– C bond angle is 120° so molecule is in planar geometry and each C atom is sp2 hybridised. 56

Brilliant STUDY CENTRE CHEMISTRY -2023 Each C atom left on one unhybridised p orbital and there unhybridised p orbitals sidewise overlapping to form there carbon  bond on two ways. HH HH H HH H HH HH The participation of each  orbitals to form more than one  bond is known as delocalisation and this delocalised  electrons are shown above and below the plane. According to resonance theory there  electrons are completely delocalised and there delocalised structures are called cannonical structures. PREPARATION 1. From acetylene 3CH  CH nroend thuobte 57

Brilliant STUDY CENTRE CHEMISTRY -2023 H CH C H CH CH H C C H  CH CH HC C C CH H 2. From normal hexane C6H14 V2O5 3H2 3. From sodium benzoate COOH COONa Na2CO3 NaOH NaOH+C2O 4. From phenol + ZnO OH Znndust  5. From chlorobenzene + HCl Cl NiNAaOl aHlloy 6. From benzene diazonium chloride 58

Brilliant STUDY CENTRE CHEMISTRY -2023 N2Cl- + H3PO2 + H2O Cu 2 N2 + HCl + H3PO3 O 7. From benzene sulphonic acid SO3H + H2O  + H2SO4 8. From grignard reagent C6H5MgX H2O C6H6  Mg OH X C6H6CH2MgX H2OC6H5CH3  Mg OH X 9. Wurtz Fittig Reaction Haloalkenes react with haloalkenes in presence of disodium in dry ether aralkyl compounds are formed X + 2Na + X R R + 2NaX  R  X  2Na  X  R  R  R  2NaX - Wurtz reaction X + 2Na + X  + 2NaX Fitting reaction PHYSICAL PROPERTIES As size increases melting point and boiling point increses. In benzene each  electrons are equally attracted by all carbon atoms so dipole moment is zero.  So boiling point depends only on size. • In case of isomeric, P isomers having high melting point than M and O due to symmetric geometry. • Benzene insoluble in water but soluble in organic solvent CHEMICAL REACTIONS • More reactive than alkanes and less reactive than alkenes and alkynes due to complete delocalisation of electron. ELECTROPHILIC SUBSTITUTION REACTION 1. E - Nu ionise E + Nu 59

Brilliant STUDY CENTRE CHEMISTRY -2023 E E E 2. H H Arenium ion H E 3. E + H-1 1. Generation of electrophile Cl 2. Formation of arenium ion + HCl 3. Formation of sub product 1. HALOGENATION + Cl2 anhy:AlCl3    AlCl3 Cl Cl Cl Cl H Cl AlCl3 Cl + AlCl4 Al Cl3 Cl- + HCl + AlCl3 H Cl AlCl3 acts as a halogen carries as well as electrophilic producer. If a halogen carries is present and no light then benzene goes subtraction. Br + Br2 FeBr3 + HBr 60

Brilliant STUDY CENTRE Br Fe B r3 CHEMISTRY -2023 H Br + Br - Br FeBr3 Br + HBr + Cl Cl Cl + 6Cl2 AlCl3  + 6HCl Cl Cl Cl hexachlorobenzne 2. Nitration conc:H2SO4  NO2 HNO3 + H2O H2SO4 H  HSO4 H H H2O + NO2 OH NO2 O NO2 H + NO2  NO2 HSO4 NO2 H + H2SO4 Sulphonation SO3H conc. H2SO4 / H2S2O7 Oleum 2H2SO4 SO3 + H3O + HSO4 61

Brilliant STUDY CENTRE CHEMISTRY -2023 O S HO HSO4 OO H2SO4 S O SO3H + H2O O O H HO H S O O 1. ALKYLATION FRIEDEL CRAFT REACTION R R Cl + HCl An. AlCl3 R Cl + AlCl3 R Cl AlCl3 R C l A lC l3 R Cl Cl3 R H + HCl + AlCl3 Al 2. ACYLATION O O CR R C Cl An.AlCl3 + HCl O A lCl3 R C Cl 62

Brilliant STUDY CENTRE CHEMISTRY -2023 BENZENE ADDITION REACTION Cl Cl HH H Cl Cl H Benzene hexachloride + 3Cl2 30h0K H Cl H Cl + 3H2 42N6iK OXIDATION REACTION 2C6H6  15O2 12CO2  6H2O When benzene burn with air/oxygen under pressure, they burn with an yellow sooty flame. This flame indicate presence of higher carbon content in benzene and is used for distinguishing diphetic and aromatic compound. Incomplete oxidation O CH COOH C + 9 2 O2 V2O5 CH COOH H2O CH O Maleic anhydride CH C O Oxidation with KMnO4 Benzene resist KMnO4 oxidation but alkyl benzenes give benzoic acid due to high reactivity of benzylic hydrogen oxidaiton taking place at benzylic carbon. CH3 COOH CH2 CH3 COOH HKM/OnOH4 HKM/OnOH4 CH3 COOH CH CH3 KMnO4  63

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 CH3 C CH3 No reaction due to KMnO4 the absence of benzyl hydrogen + 3O3  ZnH2O 3 Cl C C H OO AROMATICITY According to molecular orbital theory compounds containing (4n + 2)  electrons are completely delocalised. Such compounds are called aromatic compounds. Conditions: • Cyclic • Planar • Conjugated • Satisfy (4n + 2)  rule 4n + 2 = 6 n=1 Compounds satisfying 4n e rule  antiaromatic Others are non aromatic • 4n + 2 = 10 n = 2 aromatic • not conjugated  non aromatic 4n + 2 = 0 • n = 0 aromatic 64

Brilliant STUDY CENTRE CHEMISTRY -2023 • Non aromatic n=1 aromatic • aromatic n = 1 O Aromatic n = 1 • aromatic N NH • antiaromatic Directive Influence of substituents It is the ability of atoms ie group to direct the incoming group to a particular position in benzene ring 1. Ortho-para directing group Atoms or group which donate electrons towards benzene ring and increases electron density in o and p positions. These group are ring activating groups. All electron donating groups are o and p and ring activators. H H H H H CH H CH H C H+ H C H+ OH OH OH OH META DIRECTING GROUP Atoms or group which withdraw electron from benzene rings and decreases electron density at o and p positions. These groups are ring deactivating group. All electron withdrawn groups are metal directing and electron withdrawing. 65

Brilliant STUDY CENTRE O O CHEMISTRY -2023 CH CH O O CH CH O O O O NO NO NO NO Here N too have l pair but act as M-group because look at the atom near the l-pair if it is high electronegative then it act as M-group. Polynuclear hydrocarbon Compounds containing more than one fused benzene ring. These can generate cancer in living tissues so they are known as carcenogenic compound and the nature is called carcinogenicity. The main source of polynuclear hydrocarbon is coal tar. PNH O2  PNH H2O PNH  CANCER Epoxide hydroxy epoxides 1 1-2 benzanthracene 2 CH3 91 2 10 9-10 dimethyl benzanthracene CH3 66

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 Methylchlolanthrene Benzpyrene Pyrene Melting point of alkane The mp of n - alkanes are not a regular pattern. Alkanes having even number of C atom have higher mp than corresponding alkane with odd no. of carbon ie next & previous. This effect is known as alternating effect / oscillating effect. Conformations of cyclohexane Several 3D shapes that a cyclohexane molecule can assume while maintaing the stability of its chemical bonds cyclohexane ring tend to assume certain non planar conformations and which bond angle closer to 109°.5 and lower the strain energy. Chair Half chair Boat Twist boat Two type Hydrogen atoms- Axial and equatorial HH H Ha Ha Ha H He He He H H Ha Ha He H H H He He H H Ha H 67

Brilliant STUDY CENTRE CHEMISTRY -2023 Axial H Flagpole Hydrogen HH HH Stability order Chair  Twist boat  Boat  Half Chair 1, 2 Cis 1a 2e 1, 2 Trans 1e 2e MS 2e LS 1a 3e MS 1,3 Cis 1e 3a LS 3e la He 1,3 Trans 1a 4e MS 1, 4 Cis 1a 4a LS 1, 4 Trans 1e 1a • MS– More stable • LS–Least stable 68