Organic Chemistry Ch. 9 - Alkyne Reactions

type of rxn forming alkynes

E2 from dihalide

geminal dihalide

halides on same carbon

vicinil

halides on adjacent Cs

reagents for alkynide ion formation

NaNH2 & NH3

reagents to protonate alkynide ion

excess NaNH2, NH3 & H2O

rxn to reduce

catalytic hydrogenation

reagents to fully reduce alkynes via catalytic hydrogenation

H2

Pt/Pd/Ni

reagents to isolate intermediate in reduction of alkyne via catalytic hydrogenation - syn/cis

Lindlar’s catalyst, P-2 (Ni2B)

reagents to isolate intermediate in reduction of alkyne via catalytic hydrogenation - anti/trans

Na

NH3

reagents alkyne hydrohalogenation markovnikov

H-X

reagents alkyne hydrohalogenation antimarkovnikov

H-X 

ROOR

when does alkyne hydrohalogenation form geminal dihalide

excess reagents used (rxn occurs 2X)

alkyne hydrohalogenation is reverse of…

dihalide eliminations

reagents acid-catalyzed hydration of alkynes markovnikov 

H2SO4 & H2O

NaOH

similar to oxymercuration - demercuration

product of acid-catalyzed hydration of terminal alkynes markovnikov 

enol that tautomerizes into methyl ketone via acid-catalyzed keto-enol tautomerization

reagents acid-catalyzed hydration of alkynes antimarkovnikov

R2BH or H2O2 &NaOH

product of acid-catalyzed hydration of terminal alkynes antimarkovnikov 

aldehyde

tautomerization

rapid interconversion of 2 constitutional isomers (tautomers) via proton transfers

what acid-catalyzed keto-enol tautomerization looks like

ok it’s not showing up but know this

hydroboration-oxidation of alkynes reagents

R2BH (dialkylborane)

hydroboration-oxidation of alkynes markovnikov or antimarkovnikov

anti-markovnikov

product of hydroboration-oxidation of alkynes

enol that tautomerizes into ketone via base-catalyzed keto-enol tautomerization

reagents for halogenation of alkynes dihalide

one equivalent X2

CCl4

reagents for halogenation of alkynes tetrahalide

excess (2X+) X2

CCl4

halogenation of alkynes stereoselectivity

mainly anti, some syn

product of ozonolysis of internal alkynes

2 carboxylic acids

product of ozonolysis of terminal alkynes

carboxylic acid & CO2

reagents ozonolysis of alkynes

O3

H2O

largest difference between alkynes and alkenes

alkylation

alkylation

can change the number of C-C bonds and add/change functional groups, terminal alkynes easily deprotonated to alkynide ions which are strong nucleophiles & bases

alkylation of acetylene

2 successive alkylations

reagents for alkylation

1) NaNH2

2) RX

general synthesis strategy alkene to alkyne

1) halogenation 2) elimination