Ch04 Alkenes and Alkynes

8/18/2019 Ch04 Alkenes and Alkynes

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WILLIAM H. BROWN

THOMAS POON

www.wiley.com/college/brown

C H A P T E R F O U R

Alkenes and Alkynes

Copyright© 2014 John Wiley & Sons, Inc. All rights reserved.


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Unsaturated Hydrocarbons

• Unsaturated Hydrocarbon: Contans one o!

"o!e #a!$on%#a!$on do&$le o! t!'le $onds o!

$en(ene%lke !n)s.

* Alkene: #ontans a #a!$on%#a!$on do&$le $ond

and +as t+e )ene!al ,o!"&la CnH-n. * Alkyne: #ontans a #a!$on%#a!$on t!'le $ond

and +as t+e )ene!al ,o!"&la CnH-n%-.

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.


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Unsaturated Hydrocarbons

• Arene: $en(ene and ts de!ates /C+ 01



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Benzene and Phenyl Groups

• We do not st&dy $en(ene and ts de!ates

&ntl C+a'te! 0.

* Ho2ee!3 2e s+o2 st!t&!al ,o!"&las o,

#o"'o&nds #ontann) a '+enyl )!o&' $e,o!e t+at

t"e. * T+e '+enyl )!o&' s not !ea#te &nde! any o, t+e

#ondtons 2e des#!$e n #+a'te!s 4%5.



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Structure of Alkenes

• T+e t2o #a!$on ato"s o, a do&$le $ond and

t+e ,o&! ato"s $onded to t+e" le n a 'lane3

2t+ $ond an)les o, a''!o6"ately 7-89.



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Structure of Alkenes

• A##o!dn) to t+e o!$tal oe!la' "odel3 a

do&$le $ond #onssts o, one σ $ond ,o!"ed

$y oe!la' o, sp- +y$!d o!$tals and one π

$ond ,o!"ed $y oe!la' o, 'a!allel - p

o!$tals.• Rotating by 90°breaks the pi bond.



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Cis-Trans Isomerism

• Be#a&se o, !est!#ted !otaton a$o&t a C*C

do&$le $ond3 )!o&'s on ada#ent #a!$ons a!e

et+e! cis o! trans to ea#+ ot+e!. * Be#a&se o, non$onded nte!a#ton st!an $et2een

alkyl s&$stt&ents o, t+e sa"e sde o, t+e do&$le$ond3 a trans alkene s "o!e sta$le t+an an

so"e!# cis alkene.



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Structure of Alkynes

• T+e ,&n#tonal )!o&' o, an alkyne s a

#a!$on%#a!$on t!'le $ond.

• A t!'le $ond #onssts o,:

* One σ $ond ,o!"ed $y t+e oe!la' o, sp +y$!d

o!$tals. * T2o π $onds ,o!"ed $y t+e oe!la' o, sets o,

'a!allel - p o!$tals.



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Nomenclature of Alkenes

• IUPAC No"en#lat&!e o, alkenes

* Use t+e n,6 -en- to s+o2 t+e '!esen#e o, a

#a!$on%#a!$on do&$le $ond.

* N&"$e! t+e 'a!ent #+an to )e t+e 7st #a!$on o,

t+e do&$le $ond t+e lo2e! n&"$e!. * Follo2 IUPAC !&les ,o! n&"$e!n) and na"n)

s&$stt&ents.

* Fo! a #y#loalkene3 t+e n&"$e!n) o, t+e ato"s o,

t+e !n) t+e "&st $e)n 2t+ t+e t2o #a!$ons o,

t+e do&$le $ond.



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• IUPAC no"en#lat&!e o, alkenes


-He!ene


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• So"e alkenes3 'a!t#&la!ly lo2%"ole#&la!%

2e)+t ones3 a!e kno2n al"ost e6#l&sely $y

t+e! #o""on na"es.



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"onfi#uration$ Cis-Trans

• %he cis-trans system: Con,)&!aton s

dete!"ned $y t+e o!entaton o, ato"s o, t+e"an #+an.



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"onfi#uration$ &'(

• To Ass)n an E3; #on,)&!aton3 ,!st ass)n a '!o!ty

to t+e s&$stt&ents on ea#+ #a!$on o, t+e do&$le$ond. * I, t+e )!o&'s o, +)+e! '!o!ty a!e on t+e sa"e sde o, t+e

do&$le $ond3 t+e #on,)&!aton s Z /


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"onfi#uration$ &'(

• P!o!ty !&les

7. P!o!ty s $ased on ato"# n&"$e!= t+e +)+e! t+e ato"# n&"$e!3t+e +)+e! t+e '!o!ty.

-. I, '!o!ty #annot $e ass)ned on t+e $ass o, t+e ato"s $onded

d!e#tly to t+e do&$le $ond3 look to t+e ne6t set o, ato"s= '!o!ty s

ass)ned at t+e ,!st 'ont o, d,,e!en#e.



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"onfi#uration - &'(

>. Ato"s 'a!t#'atn) n a do&$le o! t!'le $ond a!e

#onsde!ed to $e $onded to an e?&alentn&"$e! o, s"la! ato"s $y sn)le $onds.



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"onfi#uration - &'(

• &!ample: Na"e ea#+ alkene $y t+e E,Z

syste" and s'e#,y ts #on,)&!aton.



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Cis-Trans Isomerism

* T+e #on,)&!aton o, t+e do&$le $ond n

#y#lo'!o'ene t+!o&)+ #y#lo+e'tene "&st $e cis.T+ese !n)s a!e not la!)e eno&)+ to

a##o""odate a t!ans do&$le $ond.

* Cy#loo#tene s t+e s"allest #y#loalkene t+at #an

a##o""odate a trans do&$le $ond.



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Cis-Trans Isomerism

• @enes3 t!enes3 and 'olyenes

* Fo! an alkene 2t+ n #a!$on%#a!$on do&$le $onds3 ea#+o, 2+#+ #an s+o2 cis-trans so"e!s"3 )n cis-trans

so"e!s a!e 'oss$le.

* Consde! -3%+e'tadene= t +as ,o&! cis-trans so"e!s3

t2o o, 2+#+ a!e d!a2n +e!e.



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Cis-Trans Isomerism

* ta"n A +as ,e C%C do&$le $onds.

* Fo&! o, t+e ,e #an s+o2 cis-trans so"e!s".

* ta"n A s t+e all%trans so"e!.



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Physical Properties

• Alkenes and alkynes a!e non'ola! #o"'o&nds.

* T+e only att!a#te ,o!#es $et2een t+e! "ole#&les

a!e dispersion forces.

• T+e '+ys#al '!o'e!tes o, alkenes and alkynes

a!e s"la! to t+ose o, alkanes o, s"la! #a!$onskeletons.

* T+ose t+at a!e l?&d at !oo" te"'e!at&!e a!e less

dense t+an 2ate! /7.8 )"L1.

* T+ey dssole n ea#+ ot+e! and n non'ola! o!)an#

solents.

* T+ey a!e nsol&$le n 2ate!.



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%he Acidity of %erminal Alkynes

• One o, t+e "ao! d,,e!en#es $et2een t+e

#+e"st!y o, alkynes3 and alkanes and alkeness t+at t+e +yd!o)en ato" o, a te!"nal alkyne s

s&,,#ently a#d# /'K a -41 t+at t an $e !e"oed

$y a st!on) $ase s+ as sod&" a"de3 NaNH-3to )e an alkyne anon.



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• Be#a&se 2ate! /'K a 74.D1 s a st!on)e! a#d

t+an a#etylene o! a te!"nal alkyne3

+yd!o6de on s not a st!on) eno&)+ $ase ,o!

an a#d%$ase !ea#ton 2t+ a te!"nal alkyne.



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• T+e 'K a al&es ,o! alkane and alkene

+yd!o)ens a!e so la!)e t+at no $ase s st!on)

eno&)+ to !e"oe a +yd!o)en ,!o" et+e! o,

t+ese #lasses o, #o"'o&nds.



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• Ho2 do 2e a##o&nt ,o! t+e a#dty o, a te!"nal alkyne

#o"'a!ed to an alkane o! alkene

• To ans2e! t+s ?&eston3 2e "&st ,o#&s on t+e sta$lty

o, t+e anon de!ed ,!o" ea#+ #lass o, +yd!o#a!$on.

• T+e lone 'a! o, ele#t!ons o, an alkane anon les n ansp> +y$!d o!$tal3 2+#+ +as -4 s #+a!a#te!.

• Fo! an alkene anon3 t+e lone 'a! les n an sp- +y$!d

o!$tal3 2+#+ +as >> s #+a!a#te!.

• Fo! a te!"nal alkyne anon3 t+e lone 'a! les n an sp

+y$!d o!$tal3 2+#+ +as 48 s #+a!a#te!.



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• T+e )!eate! t+e s #+a!a#te! o, t+e o!$tal

$ea!n) t+e ne)ate #+a!)e3 t+e )!eate! t+esta$lty o, t+e anon3 and t+&s t+e )!eate!

a#d# t+e +yd!o)en !e"oed.

• O, t+e se!es o, #o"'o&nds alkane3 alkene3and alkyne3 t+e #a!$on o, a te!"nal alkyne s

t+e "ost ele#t!one)ate /48 s #+a!a#te!1.

T+e!e,o!e3 a te!"nal alkyne anon s t+e"ost sta$le o, t+e se!es3 and a te!"nal

alkyne s t+e "ost a#d#.



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Ho* to determine the Inde! of Hydro#en +eficiency ,IH+

Bass a!e t+e Sat&!ated HCs /Alkanes1 CnH-nG-

E6 CH

CH7

−

C H

5

-

Copyright© 2014 John Wiley & Sons, Inc. All rights reserved.

4 douleonds! d & 1 ring

2d & 2 rings1 d & !rings2 tripleonds

H-

C C CH CH C CH-

HC C CH-

CH-

C CH


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Alkenes and Alkynes


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Ch04 Alkenes and Alkynes

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