Alkynes

Reaction

Acidity

Synthesis

Complex of Acetylene

Bonds

Hydrocarbon Comparison

Alkyne Nomenclature

HC CCH2CH2CH3

1-pentyne 4-decyne

CH2C C CH3

3-(2-butynyl)cyclohexene 5-phenyl-1-hepten-6-yne

Enes with Ynes

chain numbered from end closest to -bond

1 57

7,8-dimethyl-5(E),7(Z)-decadien-1-yne

tie goes to the alkene

NH

O

O

OH

OH OH

CO2H

OCH3

CH3

O

Dynemycin AAntitumor antibiotic

Catalytic Hydrogenation

75 psi

H2 - 1%Pt on C

Lindlar’s Catalyst

H2 on a Poisoned Catalyst Prevents Over-Reduction

cis Alkenes

5-decyne

H2 / Pd on BaSO4

quinolineLindlar's catalyst H H

H2, 1%Pt on C

Addition of HX

CH3CH2C CHHBr

CH2CH3CH2C

BrHBr

CH3CH2CCH3

Br

Br

Br2 Addition

C CH Br2C C

HBr

Br

C

Br

Br

C

Br

Br

H

Br2

Hydration: OxymercurationMarkovnikov

CH3CH2C CHHgSO4, H2SO4

H2OCH3CH2C=CH2

OH

an enol

CH3CH2CCH3

O

a ketone

Enol – Keto TautomerizationIntermolecular

3

OH

CH

HCH3CH2C

OH

CH

HCH3CH2C

OH

CH

HCH3CH2C

CH3CH2CCH3

O

Oxymercuration Mechanism

enol

SO42-SO42-

H3O+

tautomerization

OH

CH

HCH3CH2C

H2O

CH3CH2C CHg

HOH

O

CH3CH2CCH3

H2OO

HH

CHg

HCH3CH2C

vinyl carbocation

Hg+2

CH3CH2C CHg

H

HgSO4, H2SO4(aq)CHCH3CH2C

Hydration: HydroborationAnti-Markovnikov

2) H2O2, NaOH

1) disiamyl borane

O

CH3CH2CH2CH

CHCH3CH2C

an enol

OH

CH3CH2CH=CH2

an aldehyde(sia)2BH

B

H

Hydroboration Mechanism

CH3CH2C CH CH3CH2CH2CH

O1) disiamyl borane

2) H2O2, NaOH

B

H

(sia)2BH

CH3CH2C

H

CH

B(sia)2H2O2, NaOH

CH3CH2CH=CH2

OH

enol

tautomerization

Draw the Products

C CH1) disiamylborane, THF

2) H2O2, NaOH

HgSO4, H2SO4 (aq)

C CH1) disiamylborane, THF

2) H2O2, NaOH

HgSO4, H2SO4 (aq)

CH2CH

CCH3

O

O

Acidity of Terminal Alkynes

Acetylide Formation

Alkylation of Acetylide IonsHomologations using SN2 rxn

CH3CH2CH2C C HNaNH2

in NH3(l)-78 C

o

CH3CH2CH2C C Na

CBr

H

HH

CH3CH2CH2C CCH3

SN2NH2

Multi-step Syntheses

HC CH Br?

Retrosynthetic AnalysisBegin with the Product

HC CH Br?

Fill in the Reagents

HC CH Br?

1) NaNH2, NH3

2) Br

H2, Lindlar's cat.

HBrROOR, h

How Many Steps?

CHHCCH2CH(CH3)2

H

H

CH3

?

5 Steps

CHHCCH2CH(CH3)2

H

H

CH3

1) NaNH2, NH3

2) CH3I

3) NaNH2, NH3

4) (CH3)2CHCH2Br5) Li, NH3

Compound A, C9H12, absorbs 3 equivalents of H2 on catalytic reduction over palladium to give B, C9H18. On reaction with acidic KMnO4, compound A gives, among other things, a ketone that was identified as cyclohexanone. On treatment with NaNH2 in NH3, followed by addition of iodomethane, compound A gives a new hydrocarbon C, C10H14. What are the structures of A, B and C?

O

cyclohexanone