Addition Reactions Notes PDF

# Addition Reactions ## Step 1: Attack of pi bond on the electrophile forms a carbocation - Rich electron density - Geometry of carbocation: planar ## Addition of hydrogen halide to alkenes - CH₂=CH₂+ HX → CH₃-CH₂ + X- - **Symmetric alkine:** Equal no. of carbons around the double bond - CH₃-...

# Addition Reactions ## Step 1: Attack of pi bond on the electrophile forms a carbocation - Rich electron density - Geometry of carbocation: planar ## Addition of hydrogen halide to alkenes - CH₂=CH₂+ HX → CH₃-CH₂ + X- - **Symmetric alkine:** Equal no. of carbons around the double bond - CH₃-CH=CH₂ + HX → CH₃-CH-CH₃ - (Propene) - CH₃-CH₂-CH₂ - (forms easily) (more stable) - Intermediate: secondary carbocation - CH₂CH₂CH₂X - (stability of secondary carbocation) ## Step 2: Attack by a nucleophile gives the product of addition: - Addition reactions are usually exothermic. ## Mechanism - **Asymmetric alkene:** Markonikov product - **Symmetric alkene:** - **Step 1:** Protonation of the double bond forms a carbocation. - **Step 2:** Bromide ion attacks the carbocation. - **Harkonikov's Rule:** - **CH3 CH = CH2:** - HBy - slow - CH3 CH₂CH₂ B - CH₂CH₂CH₂BY - slow 1-Bromopropane - (little formed) - CH3CHCH₃ BX - fest - CH3 CH CH3 - BM - 2- Bromopropane - (main product) - **R-CH-R:** - Br - predominate - product - highly selected - substituted - alky halide - **Markonikov's Rule:** - **Free energy:** - CH3CH2CH2Br - CH3CHBrCH3 - (secondary carbocation/ lesser energy) - **Stereochemistry of the iconic addition to an alkene:** - CH₃ CH₂CH=CH₂+HX → CH3CH2CH-CH3 (generation of stereocenter) - 2-halobutane contains a chiral center - exists as a pair of enantiomers - Carbocation is trigonal planar and thus is achiral. - Equal probabilities of Rand's isomers - **Skeletal Reaction:** - CH3-CH-C=C H -H ## Exception to Markonikov's Rule - **Peroxide, free radical addition:** - Industrially important free radical mechanism: - CH3-CH=CH2 + HBr (peronides) - → CH3 CH₂CH₂Br - (CH3)2C=CH2 + HBr (peronides) → (CH3)2CHCHBr Polymer synthesis - **Anti Markonikov's Rule/Mechanism:** - CH3-CH=CH2 + HX - Perovide - CH3-CH=CH2 (H202/203 - HBr H°+ Br - → CH3-CH-CH₂вя + Н→ CH3CH₂CH₂ Вя - CH₂CH₂+ H₂SO₄ → CH3-CH₂ - HSO4 - CH₂CH₂HSO4 H2O CH3CH2OH + H2SO4 - CH3-CH=CH2 + H HS04 - → CH3-CH-CH H -H₂O - CH₂CH₂CH₂HS04 - CH3CH-CH3 -HS04 - →(carbocation) - 3HSO4 - → CH3CHCH3 + H₂S04 -OH - →Propan-2-ol - → Isopropyl alcohol - CH3-CH=CH2+HU→ CH3-CH-CH3 - Ce - **Anti- Markonikov Addition (most stable free radical mechanism):** - **Chain initiation:** - Step 1) R-öfo-R heat, 2R-O- - Heat brings about homolytic cleavage of the weak oxygen-oxygen bond. - Step 2) R-O + HBr: R-O:H+: Br. - The alkyl radical abstracts a hydrogen atom from HBr, producing a bromine radical. - **Chain Propogation:** - Step 3) : Вя. + H₂C=CH-CH3: Br: CH2-CH-CH2 - A bromine radical adds to the 2° Radical double bond to produce the more stable 2° alkyl radical. - Step 4) : Bis-CH2-CH-CH₂ + H.Pr. HBr: → : Br-CH2-CH-낼 - The alkyl radical abstracti a hydrogen atom from HBr. This kads to the product and regenerates a bromine radical. - Then repetitions of steps 3 and 4 lead to a Chain reaction. ## Addition of sulfuric acid - Alkenes + cold con sulfuric acid → alkyl hydrogen sulfates - Propene + conc 4 S04 - H - C=CH₂ - CH₃( - C-CH-H -H - → - /+ - CH₂ - HOSOH - H - →CH₃-C-CH₃ :O -OSO3 H - :O SOH - 2° Carbocation - (more stable - Carbocation) - Isopropyl - hydrogen - Sulfate - 2-Methylpropune (Isobutylene) - CH3 -CH2 -CH₃ - → Tertiary carbocation - OSO3H - →Tertiary carbocation ## Mechanism (Markonikov Addition) - **Step 1)** - CH3-C+ - CH₂ + H-HS CH₃- CT - HJCLCH₃ - CH3 - **Step 2)** - CH3 - Ct - CHÍCH - +H-O-H - fast - CH3 H - CH₂-H - CH3 - + - H - H-Q: - +:0-H CH₃-¿-O-H (protonated - CHH - CH-CO+-H - CH3 - 1 - CH₃ - + - alcohol) - **Step 3)** - CH3 - CH--Ö-H + H-O-H - CH3 - (Alcohol) - **Acid Catalysed Hydration - H3O+ Addition** - **Addition reaction → exergonic** ## Mechanism (Ionic-Markonikov Addition) - **Step 1:** Protonation of the double brond forms a carbocation. - H - CH3-C=C-CH₃ - H-B - H - CH3-C--CH₃ + : Br: - **Step 2:** Bromide ion attacks the carbocation - HH - CH-C-C-CH₃+: Br: CH3- - H - + - H H - C-C- - C-CH3 - Н: Вя: ## Thermodynamics of Addition-Elimination Reactions: Equilibria - **CH3** - **ναxίνομαι GJ CH₂+ H₂O** - **H3C** - **(+** - **HO** - **H2SO4 H3C** - **C-OH** - **H₃C-1** - **H₃C** - **Bonds broken** - **C=CT bond**: 243 KJ/mol - **H-OH**: 497 KJ/mol - **▲6° = -5.4 KJ/mol** - **• ΔΗ° = -52.7 KJ/mol** - **As =** -0.16 KJ/mol - **Bonds formed** - **H3C-2C-H**: -410KJ/mol. - **(H3C) 3C-OH**: -380kJ/mol - **Le Chatelier's Principle:** - **Temperature is increased:** Elimination Reaction - **Temperature is decreased:** Addition Reaction - The hydration -dehydration equilibria is altered - **toward hydration (alcohol):** by adding dilute acid at low temperature. - **toward alkene (dehydration):** by adding concentrated acid at high temperature. ## Oxymercuration Hydration - **Regiospecific reaction - Harkonikov addition:** - H - + - H - 1) Hg (OAC) 2 in - THP/H2O - H - 2) NaBH4 - OH - → sodium borohydrate - (powerful reducing - agent) - **Add the OH to the carbocation part** - OAC Mercuric Acetate - Hg(OAC)2 - (+) - Eg1) CH3-CH=CH-CH₃ - (carbocation) - Eg 2) CH3OH - CH3-C=C-CH3 - H2 - H - Eg 3.) F.S2- - HA - + - H - Fertiary secondary - H carbocation - H - + - OH - (H) - Tertiary & evilenginet - carbocation ruteniqu - • evertongmet wal los bias urwit Tertiary - carbocation - sutvagnat doin to BUDD ## Hydroboration Hydration - **Anti Markonikov** - 3 - → free radical - OH - Draw the major products - 1) BH3-THF - H2O2, NaOH - 1) BH3, THF - CH3 - 2) H₂O, NADH - OH - H - + enantiomer - CH3 - (chiral - carbon) - 1) Hg (OAC) 2, H₂O-THF - 2) NaBH4 - → Not an asymmetric - Carbon - OH - CH3 - H - Enantiomeric - structure - OH - CH3 - H - **Electrophilic Addition of Br2/Cl₂ to Alkenes** - Alkenes react rapidly with Br2 and ce in non-nucleophilic solvents to form vicinal dihalides. - B - Br+ Br - Br - + - Br - Br - Br - Addition of halogens is an anti addition to the double bond - H - = - H - Br+ - H - H - B- ## Stereo specific reaction - Cis-2-butene and trans-2-butene are diastereomers - HO - WAH - CH3 - Reaction 1) - H - CH₃ - trans-2-butene - Br - Br - сеч - AHTEHA - (1 - Brz - Reaction 2) - H - H - CCl4 - NO - CH3 - CH₃ - → - Cis-2-butene - Br - H - HII HE - CH3 - CH3 - H - Br - CH₃ - Br - H - HII HE - CH3 - + CH - Br - Br - CH3 - (2R,SS)-2,3-Dibromobutane - (a meso compound) - (2R, 3R) - CH3 - (23,35) - (a pais of enantiomers) ## Halohydrin Formation - HO - S+ 8- - Br-Br - Br: - + - Br2 in H₂O - OH - H - BA - ↑ - Br - bromonium ion 40: - Br - BA - > (anti addition) - OH - と - sitikto itno no di aragaled fo ritiko A - Is med Nduals