Title 13. HYDROCARBONS.pdf ✅

ARENES HC CH Most of them are odourless except for thyne Soluble in none-polar soluents and insoluble in water Boiling point of alkene increases as the chain length increases Boiling point decreases with increase in the branching First few members of alkynes are gases PHYSICAL PROPERTIES Immiscibel in water but completely soluble in polar Increase in branching leads to decrease in boiling point Alkenes are insoluble in water but soluble non-plar solvents Alkenes have a short odour Characteristic smell Burn with a sooty flame Highly notatile in nature PHYSICAL PROPERTIES First few members are gases and rest are liquids & solids. PREPARATION From Calcium Carbide From Vicinal dihalides CaO + 2H2 O C2 H2 + Ca(OH)2 BrCH2—CH2 Br CH CH + 2H2 O+ KBr alc. KOH ∆ CHEMICAL PROPERTIES CHEMICAL PROPERTIES CH2 ==CH2 H2 Br2 HCl/CH3 COOH H2 O Hg2+, H+ H2 Pt, Pd, Ni CH2 —CH2 CH==CH Br Br CH2 ==CHCl — — CH2 ==C—H OH — HC CH POLYMERISATION LINEAR POLYMERISATION High temp./ High pressure Cyclic polymerisation Red hot 873 K Iron tube —( C==C—C==C—) H H H H Electrophilic Bustitution Reaction Addition Reaction —NO2 —Cl —CH — 3 HSO3 —C— O CH3 —— Conc. HNO3 Anhyd. Alcl3 + CH3 COCl Conc. H2 SO4 (323-333 K) Conc. H2 SO4 + SO3 Anhyd. Alcl3 + Cl2 Anhyd. Alcl3 + CH Cl 3 — — — — — — Cl Cl Cl Cl Cl Cl 3H2 , Ni ∆ 3Cl2 , UV 500 K ALKANES Cn H2n-2 PHYSICAL PROPERTIES ALKANES ARE HYTROPHOBIC GENERALLS, NON-POLAR IN NATURE BOILING POINT INCREASES WITH INCREASE IN BOILING POINT DECREASES WITH INCREASE IN BRANCHING Staggered Eclipsed H H H H H HH H H H H H Newman Projection Sawhorse Projection Eclipsed Staggered CONFORMERS PREPARATION CHEMICAL PROPERTIES CHEMICAL PROPERTIES ADDITION OF HYDROGEN HALIDES From unsaturated hydrocarbons CH2 ==CH2 CH3 —CH3 Pt/Pd/Ni H2 From alkyl halides CH3 —CH2 —Cl CH3 CH3 + Na Zn H+ 2CH3 —Na CH3 CH dry ether 3 WURTZ RX From carboxylic acids (Kolbe's Electrolytic Method) CH3 —CH2 —Cl CH3 CH3 + Na Zn H+ 2CH3 —Na CH3 CH dry ether 3 WURTZ RX PREPARATION —COONa Decarboxylation of carboxylic acids NaOH ∆ + Na2 CO3 —OH Reduction of Phenol Using Zn Dust Zn ∆ + ZnO PREPARATION 1, 2-benzanthvacene 1, 2-benzpyrene CARCINOGENICITY AND TOXICITY Aromatics are toxic in nature and most of them are classified as carcinogens. HUCKEL'S RULE OF AROMATICITY 1. Planarity 3. Presence of (4n + 2)-p electrons 1. INITIATION Substitution Reaction Halogenation 2. Delocalisation of of π-electrons Cl2 Cl + Cl hv Combustion 3. TERMINATION Cl + Cl Cl2 CH3 + Cl CH3 Cl ELECTROPHILIC REACTIONS 2. PROPAGATION Cl4 + Cl CH3 + HCl CH3 + Cl—Cl CH3 + Cl CxHy + (x + y/4)O2 xCO2 + y/2H2O Controlled Oxidation CH4 + O2 2CH3 OH 10 atoms Cu/523 K CH4 + O2 HCHO + H2 O Mo2 O3 Isomerization 2CH3(CH2)4CH3 Anhyd. Alcl3 HCl Aromatic Reforming 10-20 atm Cr2 /O3 773 K Reaction with Steam CH4 + H2O CO + 3H2 Ni Pyrolysis PHYSICAL PROPERTIES From alkynes R2 C CR1 + H2 Pd/C R2 R1 H H From alkyl halides CH3 —CH2 —X alc. KOH H H H H + Hx From vicinal dihalides Br—CH2 —CH2 —Br Zn H H H H + ZnBr2 From acidic dehydration of alcohols HO—CH2 —CH3 conc. H2 SO4 + H2 O CH3 —CH==CH2 CH3 —CH—CH3 cold conc. O—SO3 H — CH3 —CH==CH2 CH3 —CH—CH3 H2 O H+ OH — POLYMERIZATION n—( CH2 ==CH2 —) —( CH2 — CH2 —) n High temp. High pressure catalyst OXIDATION OZONOLYSIS dil. KMnO4 273 K CH2 ==CH2 + H2 O CH2 — CH2 — — OH OH R1 R3 R2 R4 + O3 O O O — R3 R3 R1 R2 Zn H2O R3 R4 O R3 R4 O + AROMATIC REFORMING CH2 ==CH2 + Br2 CH2 —CH — — 2 Br Br C6 H14 773 K C6 H12 + H2 C4 H8 + C2 H6 + H2 C3 H4 + C2 H4 + CH4 + ALKYNES C n H2n-2 MARKOVNIKOV'S RULE “Negative part of the addendum gets attached to the carbon containing lesser number of hydrogens”. (I) is major product. ANTI-MARKOVNIKOV EFFECT / KHARASH EFFECT/ APNTI-PEROXIDE EFFECT This mechanism proceeds via free radical mechanism and the minor product via Markovnikov effect becomes major product. (II) is major product. Symmetrical Alkene Asymmetrical alkene BrCH2 —CH CH2 3 ==CH2 + HBr (I) CH3 CH2 BrCH3 (II) CH3 CH2 CH2 Br CH3 —CH==CH2 + HBr ALKENES H H H H C C HYDROCARBONS