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Chapter 61 Reactions of Alkynes. Introduction to Multistep Synthesis Chapter 6.

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Presentation on theme: "Chapter 61 Reactions of Alkynes. Introduction to Multistep Synthesis Chapter 6."— Presentation transcript:

1 Chapter 61 Reactions of Alkynes. Introduction to Multistep Synthesis Chapter 6

2 Chapter 62 Contents of Chapter 6 General Formulas of Alkynes and Nomenclature Multifunctional Group Nomenclature Structure and Properties of Alkynes Reactivity Considerations Addition of Hydrogen Halides and Halogens Other Additions Hydrogenation of Alkynes Acidity of Hydrogens Bonded to sp Carbons Introduction to Multistep Synthesis

3 Chapter 63 Alkynes If the triple bond is at the end of the chain, the alkyne is known as a terminal alkyne

4 Chapter 64 Alkynes If the triple bond is not at the end of the chain, the alkyne is known as an internal alkyne

5 Chapter 65 Alkynes Common names of alkynes are based on substitution of the simplest alkyne, acetylene

6 Chapter 66 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

7 Chapter 67 IUPAC Nomenclature of Dienes Find the longest chain containing both double bonds 12345 3-butyl-1,4-pentadiene

8 Chapter 68 IUPAC Nomenclature of Dienes Use corresponding alkane name but replace the “ne” ending with “diene” “pentane” changed to “pentadiene” 3-butyl-1,4-pentadiene

9 Chapter 69 IUPAC Nomenclature of Dienes Number in the direction that gives the lowest number to a double bond 1,5-heptadiene not 2,6-heptadiene

10 Chapter 610 IUPAC Nomenclature of Dienes List substituents in alphabetical order 5-ethyl-2-methyl-2,4-heptadiene

11 Chapter 611 IUPAC Nomenclature of Dienes Place numbers indicating the double bond positions either in front of the parent compound or in the middle of the name immediately before the diene suffix 5-ethyl-2-methyl-2,4-heptadiene or 5-ethyl-2-methyl-hepta-2,4-diene

12 Chapter 612 IUPAC Nomenclature of Dienes

13 Chapter 613 Configurational Isomers of Dienes

14 Chapter 614 IUPAC Multifunctional Compound Nomenclature

15 Chapter 615 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

16 Chapter 616 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

17 Chapter 617 Relative Stabilities of Carbocations Vinyl cations are one level less stable than alkyl cations

18 Chapter 618 Crude Carbocation Stability Index Add 1 for each attached carbon. Add 1 for adjacent double bond or phenyl ring. Subtract 1 if C+ on double bond. Alkene C doesn’t count but C attached to either alkene C does.

19 Chapter 619 Halogen Addition to Alkynes Halogens add to alkynes as well as to alkenes Excess halogen leads to the addition of a second equivalent

20 Chapter 620 Addition of Water to Alkynes Water adds to alkynes in the presence of acid to yield an enol

21 Chapter 621 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

22 Chapter 622 Mercuric-Ion-Catalyzed Addition of Water to Alkynes Alkynes benefit from Lewis acid catalyst to undergo hydration. Alkenes don’t need the catalyst.

23 Chapter 623 Hydroboration–Oxidation Hydroboration of an internal alkyne leads to a ketone

24 Chapter 624 Hydroboration–Oxidation For terminal alkynes, hydroboration-oxidation leads to an aldehyde (reverse addition of water)

25 Chapter 625 Addition of Water to an Alkyne

26 Chapter 626 Addition of Hydrogen to an Alkyne

27 Chapter 627 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

28 Chapter 628 Syntheses Using Acetylide Ions Alkylation reactions work best with primary alkyl halides and methyl halides

29 Chapter 629 The thought process is known as retrosynthetic analysis and is indicated by using open arrows Introduction to Multistep Synthesis

30 Chapter 630 Alkene products made from alkynes Carbonyl products made from alkynes Alkane products made from alkenes Know reactions pgs 259-260 thoroughly Understand issues involved in proper choice of reagents thoroughly Introduction to Multistep Synthesis - Considerations

31 Chapter 631 Regioselectivity of HX + alkene/alkyne rxn Regioselectivity of 2 HX + alkyne rxn Regioselectivity of oxidative hydroboration Stereospecificity of halogenation rxn Regio/stereo/specificity of X 2 /ROH or X 2 /water rxn Stereospecificity of H 2 /Lindlar reduction Stereoselectivity of Na/NH 3 reduction H 2 with Pd/C, Pt/C, or Ni does complete reduction Carbocation rearrangements prevented with Hg(OAc) 2 RX + Na  =  R rxn works best with primary halide Introduction to Multistep Synthesis – Reagent Issues

32 Chapter 632 Introduction to Multistep Synthesis – Practice Use retrosynthetic analysis to make these:

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