Chapter 51 Reactions of Alkenes and Alkynes. Chapter 5

Chapter 52 Contents of Chapter 4 Electrophilic Addition Reactions Electrophilic Addition Reactions Carbocations Carbocations Various Addition Reactions Various Addition Reactions

Chapter 53 Mechanism for Electrophilic Addition to Alkenes Reaction of 2-butene with hydrogen bromide is typical of electrophilic addition to alkenes The reaction starts with the slow addition of an electrophile to an sp 2 carbon, resulting in formation of a carbocation The next step is the rapid addition of a nucleophile to the other sp 2 carbon

Chapter 54 Addition of Hydrogen Halides to Alkenes The more substituted carbocation is preferred

Chapter 55 Stability of Carbocations Alkyl groups (“R”s) tend to stabilize the positive charge on the sp 2 carbon of a carbocation

Chapter 56 Transition State Stability Formation of a tertiary carbocation should be faster than formation of a primary carbocation

Chapter 57 Markovnikov’s Rule Modern equivalent statement: The electrophile adds to the sp 2 carbon that forms the least stable carbocation The other carbon forms the carbocation intermediate. Predicting product: put + and – signs under carbons and electrophile and nucleophile and swap partners.

Chapter 58 Addition of Water

Chapter 59 Addition of Alcohol CCH 2 H 3 C H 3 C + CH 3 CH 2 OH H + slow H 3 C CH 3 CH 2 H electrophilic attack of H + Initiating the reaction: generating a carbocation carbocation2-methylpropene

Chapter 510 Addition of Alcohol + CH 3 CH 2 OH H 3 C CH 3 CH 2 O H 2 CCH 3 H H fast H 3 C CH 3 CH 2 H nucleophilic attack of ethanol The resulting carbocation is attacked by the nucleophilic alcohol ethanol

Chapter 511 Product Analysis

Chapter 512 Alkynes Common names of alkynes are based on substitution of the simplest alkyne, acetylene

Chapter 513 IUPAC Nomenclature of Alkynes Find the longest chain containing the triple bond and change the corresponding “-ane” ending to “-yne” The chain is numbered in direction that gives the triple bond, the lower number If the same number for the triple bond is obtained in numbering from both directions, the number for the substituent nearest the chain end is minimized

Chapter 514 IUPAC Multifunctional Compound Nomenclature

Chapter 515 IUPAC Multifunctional Compound Nomenclature The longest chain has to go past the highest-priority functional group High prio group has lowest possible number If not highest priority NH 2 is amino and OH is hydroxy substituent General form is n-substit-n-alken-n-yn-n-groupsuffix

Chapter 516 Reactivity Considerations The hydrohalogenation product is an alkene which can undergo a second electrophilic addition reaction First halogen follows alkene hydrohalogenation regioselectivity rules Second halogen goes on same carbon as first halogen

Chapter 517 Relative Stabilities of Carbocations Vinyl cations are one level less stable than alkyl cations

Chapter 518 Halogen Addition to Alkynes Halogens add to alkynes as well as to alkenes Excess halogen leads to the addition of a second equivalent

Chapter 519 Addition of Water to Alkynes Water adds to alkynes in the presence of acid to yield an enol

Chapter 520 Addition of Water to Alkynes However the initially formed enol reacts further to produce a ketone Such isomers, differing only in the placement of a hydrogen atom, are called tautomers

Chapter 521 Addition of Hydrogen to an Alkyne

Chapter 522 Acidity of a Hydrogen Bonded to an sp Carbon The conjugate bases have the following relative base strength because the stronger the acid, the weaker the conjugate base

Chapter 523 Syntheses Using Acetylide Ions Alkylation reactions work best with primary alkyl halides and methyl halides

Chapter 524 The thought process is known as retrosynthetic analysis and is indicated by using open arrows Introduction to Multistep Synthesis

Chapter 525 Alkene products made from alkynes Carbonyl products made from alkynes Alkane products made from alkenes Understand issues involved in proper choice of reagents thoroughly Introduction to Multistep Synthesis - Considerations

Chapter 526 Regioselectivity of HX + alkene/alkyne rxn Regioselectivity of 2 HX + alkyne rxn Stereospecificity of H 2 /Lindlar reduction H 2 with Pd/C, Pt/C, or Ni does complete reduction RX + NaNH 2 + H  C=C  R rxn works best with primary halide Introduction to Multistep Synthesis – Reagent Issues

Chapter 527 Introduction to Multistep Synthesis – Practice Use retrosynthetic analysis to make these: