7-1

ALKYNES - Chapter 7nomenclature - (chapt 5), structure, classificationacidity of terminal acetylenes - (chapt 4)alkylation prep - dehydrohalogenation (-2HX) or double -elimination reduction - H2/M (chapt 6) and chemicalhydroboration (chapt 6) - protonation - oxidation (hydration)enol-keto tautomerismaddition of Hg++, HX, X2, H2O (chapt 6) synthesis (chapts 6)

H2

HH

Lindlarcatalyst

[blue - chemistry from previous chapters]ss2518

7-2

Chapter 7

H3C

CH3

H

H OH

CH

H3C F

HO

CH

H3CF

O

CO

H3C

H

OH

O

CO

H3C

OH

H

+

+

XH

H2 / M

Cl

IC

H

H3C D

NC

CH

H3CD

(-):CN:

CH2

OH O

HCH3

CH3

H

Br Mg CH3

δ+ δ−

LiCu

2

nomenclature - structure, classificationacidity of terminal acetylenes )alkylation -elimination

reduction - H2/M & chemicalhydroboration - protonation - oxidation enol-keto tautomerism

addition: Hg++/H2O, HX, X2 synthesis

but first ……

7-3

Chapter 7

nomenclature - structure, classificationacidity of terminal acetylenes )alkylation -elimination

reduction - H2/M & chemicalhydroboration - protonation - oxidation enol-keto tautomerism

addition: Hg++/H2O, HX, X2 synthesis

7-4

acetylene, ethyne C C HH

Structure - two general types

C CR R'

(1) internal - R and R’ = alkyl, Aryl, etc.

<-- creates additional chemistry

(2) terminal - R = alkyl, Aryl, etc.

R C C H

8,28

7-5Alkyne Nomenclature

Common: alkyl alkyl' acetylene

C C R’R

7-6

Nomenclature:IUPAC - longest chain containing the most

important functional group(s) = root #-alkyne

add substituents with #’s4-chloro-6-cyclohexyl-5-methyl-2-hexyne

C C CH3CC

C

Cl H

H

H3C

H H

7-7

Acetylene - linear geometry - sp hybridization 180o bond angles

R-C-C-R’

-bond 180o

bond angle

CC C R’R

90o angle bond to orbitals)ß

7-8Name: ______________ seat: ____

Write the product(s) of the following reactions.

Zn:

H

H

O31.

H

H

O32. HOOH

7-9Acidity of organic compounds

HC

CCH3

pKa = 25

H-Csp

H CC CH3

H

H

>

pKa = 44

H-Csp2

H CC CH3

H

H

H

H>

pKa = 50

H-Csp3

Why ? recall chapter 4The more s-character, the more acidic the C-H bond

50% 33% 25%

7-10

Relative basicity (acidity)

also - NH2 H-NH3

C

CH3C

H

+ O

C

Li

CH3H3C

H

C

CH3C

+

Li

OHC

CH3H3C

H

C

CH3C

H

+ N

H3C

Li

H

CC

H3C

+ N

H3C

Li

HH

7-11

Acid-Base reactions

CC

H3C

+ CH2

H3C

Li

H

organometallic reagent (15)

C

CH3C

H

+ CH2

H3C

Li

7-12Acid-Base reactions

last Thursday:

:OR' or :OH

NR'

R'CCR + N

R'

R'H

R'= H = a lkyl

CCR H + Bas e CCR + Bas eH

CCR + CR'

R'

H R'CR'

R'

R'

CCH3C + OH

R'CCH3C + O

R'H CCH3C + OD

R'CCH3C + O

R'D

R' = alkyl = D

7-13

Alkylation of AcetylidesAlkylation of Acetylides

acetylide anions undergo substitution rx

form new C-C bonds

Recall RX type: substitution

with 1o alkyl halides

termed “alkylation”

7-14Alkylation of Alkylation of AcetylidesAcetylides

CCl

CH3

HH

CC

H

C

H3C

+ :Cl:HH

Na

HC C: +

Na

How do we make the anions of acetylenes?

7-15

CC

CH2

CH3

H3C CC

CH2

H3C

+ H-NH2

NH2

I CH

HHC

CCH2

CH3

H3C

Alkylation of Alkylation of AcetylidesAcetylides

HC C: CCl

CH3

+

Na

HH

CC

H

C

H3C

+ :Cl:HH

Na

7-16

Acetylide anions - 2° and 3° halides:

-eliminates (strong base, reverse of addition)

+C

BrH

C

C

CH3CH2CH3

CCH3

HH

no alkylation 2°R-X

Alkylation ofAlkylation of AcetylidesAcetylides

C H

H3CH2C

CCH3

H

+C

C

CH3

H

:Br:+

7-17Preparation: Dehydrohalogenation (-2 HX)two -eliminations2 arrangements of diBrs => same acetylene

H

C C

HR

BrRBr

H

C C

BrR

BrRH

C C RR

NH2

(1 eq.)

H

C C

R

BrR

NH2

(1 eq.+)

NH2

Br

H

NH2H

Br

7-18Preparation: Dehydrohalogenation (-2 HX)two -eliminations2 arrangements of diBrs => same acetylene

H

C C

HR

BrRBr

H

C C

BrR

BrRH

C C RR

NH2

(1 eq.)

NH2

(1 eq.+)

NH2

Br

H

H

C C

R

BrR

NH2

(1 eq.)

NH2H

Br

7-19

NH2

(2 eq. or more)

Preparation: Dehydrohalogenation (-2 HX)two -eliminations2 arrangements of diBrs => same acetylene

H

C C

HR

BrRBr

H

C C

BrR

BrRH

C C RR

7-20Preparation: Dehydrohalogenation (-2 HX)

NH2

(2 eq. or more)

H

C C

HR

BrRBr

H

C C

BrR

BrRH

C C RR

NOTE! alkenes are sources of diBrsH

C C

H

RR

Br2

two -eliminations2 arrangements of diBrs => same acetylene

7-21

H3CC C

CH3

H H

H2 M(cat)

H3CC C

CH3

H HH H

H2M(cat)

H3C C C CH3

H3CC C

CH3

H H

H2/M

syn addition (2x)

Reactions - several like C=C - additionsA. Reduction - addition of hydrogen

7-22

syn addition (2x)

Reactions - several like C=C - additionsA. Reduction - addition of hydrogen

With choice of catalyst - stop at olefin (add 1 eq H2).

[Lindlar cat.]

H3CC C

CH3

H H

H2/M

H3CC C

CH3

H HH H

H3C C C CH3

H3CC C

CH3

H H H2CaCO3 Pd/C

7-23

Chemical reduction of a triple bond.

C CH3C CH3 CH3C

CCH3

H

H

trans olefin for internal acetylenes

Nao

(liq.)NH3 ether(cosolvent)

“mechanism” - Na donates e’s, know rx as prep for trans olefins

7-24

Acetylene chemistry - recall olefin chemistry

HH

H

B HRR +

HHH

B HR

R

HHH

B HR

R

R = H, alkyl

H

B HRR +

H

B HR

R

H

B HR

R

7-25Hydroboration of an internal alkyne

H3CC

CCH3

BH

HH

+

Δ

AcOH H3C CC

H3C

H

HH3C C

C

H3C

B

H

HH

terminal

HC

CR

BH

HH

+H C

C

R

B

H

HH

H CC

R

B

H

HH

H

B

H

H

H2B-H AcOH Δ H C

C

R

H

HH

H

7-26Terminal acetylenehindered borane adds oncedi-sec-isoamylborane or HB(sia)2

AcOH Δ

HR

H H

HR

H BC

CH3

C

CH3

CH3 2

HH

+

HR

+

H B

2

HR

H B

2

7-27

HR

H Bsia

sia

HR

H Bsia

sia

AcOH Δ

HR

H H+

Terminal acetylenehindered borane adds oncedi-sec-isoamylborane or HB(sia)2

H2O2NaOH

HR

H O

Henolunstable

HR

H OH

"keto"aldehyde

tautomerism H+ transfer (O to C)

7-28internal with oxidation - ketone

C

R

C

R'

BH2

H+

CBH2

CHR

R'H2O2

NaOHC

O

CHR

R'

H

ketone

keto

enol

R'C

CR

O

H

H

7-29

C

C

HgSO4HH3C

H3C

C

C

HgSO4HH3C

CH3

OH

H2O

C

C

HgSO4HH3C

CH3O

H

H+

C

C

H

CH3

CH3OH

[+ HgSO4}

H3C C C CH3 H3C C CCH3

OH

H

HgSO4

H2O

7-30

H3C C C CH3 H3C C CCH3

OH

H

HgSO4

H2O

regiochemistry

C C HCH3C

HH

Hg++ --SO4

H2O

C CH

C

H3C

HH

Hg++

C CH

CH3C

HH Hg+

OH H

H2O

C CH

CH3C

HH Hg+

O H

C CH

CH3C

HH Hg+

OH

H+

C C

H

CH3C

HH

H

OH

H+

7-31enol-keto tautomerismH+ transfer C O

R C

C O

H R C

C O

H

R' R'

H H

from HB/[O] Hg+2/H2O other rxs

mechanism e(-) arrows

R C

C O

H R C

C O

H

R' R'

H H

R C

C O

H R C

C O

H

R' R'

H Hor

7-32

Hydration of acetylenes

internal yne

terminal yne - HBR2/[O] aldehyde

- Hg++/H2O ketone

R C C R' R CCH2R'

OR'C

RH2C

O

+

R C C H

R CH2 C

H

O

R CCH3

O

- “either” ketone(s)

7-33electrophilic additions Br2 / Cl2

C

R

C

R'

CBr

CRBr

R' Br2

1 eq.

Br2

1 eq.or XS

C

Br

CRBr

R'Br

Br

Assume bromonium (chloronium) ion ( like alkene X2 addition )

C

C

R'

R

X XC

C

R'

R

X

X

C

C

R'

R

X

X

Mechanism for 1st addition of X2

7-34

H

C

Br

CH

R'Br

H

HBr1 eq.or XS

HBr1 eq.

CBr

CH H

R'

addition of HX

C

H

C

R'

C

H

CR'

H

vinyl bromide

2o-vinyl R+

7-35

C

Br

CH

R'Br

HH

HBr1 eq.or XS

addition of HX - second addition

HBr1 eq.

CBr

CHH

R'

C

H

C

R'

CBr

CHH

R'

H

CBr

CHH

R'

H

2o carbocationwith resonance

CBr

CHH

R'H

Br(-)

1o carbocation and no resonance!

7-36

Br

H?

H

H

How could the vinyl bromide be converted into the Z-olefin? Use any number of reactions but show all necessary reagents and expected products of each step.

how?a. H2/Lindlar(cat.)or b. (1)BH3, (2)AcOH/∆

how?Na+-NH2

7-37

convert 2-bromopropeneto 2-hexanone

Br

O

O

OR

7-38Br

O

O

OR

compare carbon skeletonfunctional groups

convert 2-bromopropeneto 2-hexanone

7-39

O

O

OR

Br

compare carbon skeletonfunctional groups

O

X

X

7-40

NH2

1 eq.H

Br

HgSO4 / H2O

Br

OO

+

NH2

1 eq.

NH2

xsor

or2 equiv.

other way?