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!e"initions

Conjugateddouble bonds are separated byone single bond. Example: 1,3-pentadiene.

#solateddouble bonds are separated by twoor more single bonds. 1,4-pentadiene.

Cumulated(Alenos) double bonds are on

adjacent carbons. Example: 1,2-pentadiene.!

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$elati%e Sta&ilities

twice 1-pentene

more substituted

!

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)

Structure o" '()*utadiene

/ost stable con#ormation is planar. 0ingle bond is s$orter t$an 1.)4 .

Electrons are delocalied oer molecule.

!

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Con"ormations o"

'()*utadiene s-trans con#ormer is more stable t$an t$es-cis by 2.3 &cal.

Easily interconert at room temperature.

HH

H

H

H

H

s-trans s-cis

H

H

H

H

HH

!

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Allylic groups

(

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Allylic Cations

6arbon adjacent to 66 is allylic.

*llylic cation is stabilied by resonance.

0tability o# 1allylic 2carbocation. 0tability o# 2allylic 3carbocation.

H2C CH

CH2+

H2C CH

CH2+

!

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1,2- and 1,4-*ddition

to 6onjugated +ienes Electrop$ilic addition to t$e double bond

produces t$e most stable intermediate.

8or conjugated dienes, t$e intermediateis a resonance stabilied allylic cation.

9ucleop$ile adds to eit$er carbon 2 or 4,

bot$ o# w$ic$ $ae t$e delocaliedpositie c$arge.

!

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,inetic %s-

T.ermodynamic Control

Major productat 40C

Major product

at -80C

!

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*llylic adicals

0tabilied by resonance.

adical stabilities: 1; 2; 3; 1allylic.

0ubstitution at t$e allylic position competeswit$ addition to double bond.

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Allylic *romination

Br

H

H

HH

H

H

H

H

H

H

= HBr

Br Br Br Br

H

H

BrH

H

H

H

Br+ Br

!

Br2h

Br2

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*romination /sing *S

N->romosuccinimide 9>0 proides alow, constant concentration o# >r2.

9>0 reacts wit$ t$e ">r by-product toproduce >r2and preent ">r addition.

!

Br

!

!

+ HBr H

!

!

+ Br2

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1)

/?@s #or t$e *llylic 0ystem

!

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1

+iels-*lder eaction ?tto +iels, Aurt *lderB 9obel prie, 17)%

Croduces cyclo$exene ring

!iene= al1ene or al1yne wit$electron-wit$drawing group dienop$ile

C

C

H H

H "

C

C

H

H

"

H

!

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1(

Examples o#

+iels-*lder eactions

!

+

!C

!CH3

C

C

C! !CH3

C C

!

!CH3

C

!CH3!

C

H3C

H3C

C

CH

CHH

+

H3C

H3C

C

C

H

C

H

H

diene dienop$ile +iels-*lder adduct

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0tereoc$emical eDuirements

+iene must be in s)ciscon#ormation. +iene@s 61 and 64 porbitals must

oerlap wit$ dienop$ile@s porbitals to#orm new sigma bonds.

>ot$ sigma bonds are on same #ace o#

t$e diene: synstereoc$emistry.!

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Concerted Mec.anism

!

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2%

Endo $ule