Alkenes Structure Stability Nomenclature Alkenes - Structure, Stability, Nomenclature

28 Pages·2010·2.18 MB·English

AAllkkeenneess - SSttrruuccttuurree, SSttaabbiilliittyy, NNoommeennccllaattuurree
Also called an olefin but alkene is better
General formula C H (if one alkene present)
n 2n
uunnssaattuurraatteedd - ccoonnttaaiinn ffeewweerr tthhaann mmaaxxiimmuumm HH''ss ppoossssiibbllee ppeerr CC
Can act as weak nucleophiles
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SSttrruuccttuurree ooff AAllkkeenneess
One C-C sigma bond and one C-C pi bond
Presence of C-C pi bond prevents bond rotation!
2
DDeeggrreeee ooff UUnnssaattuurraattiioonn
Sum of all multiple bonds and/or rings in a molecule
Compared to saturated alkane (C H ) where each double bond
n 2n+2
aanndd rriinngg rreemmoovee ttwoo hhyddrrooggeennss.
DDooUU == ((HH - HH ))//22
sat actual
where H is number of hydrogens in saturated compound
sat
H is number of hydrogens in compound molecular formula
actual
andd H = 2 +2 - ##X + ##NN
ssaatt nn
X = halogens
NN == nniittrrooggeennss
(ignore other atoms)
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EExxaammppllee:: CC HH
6 10
H = 2(6) + 2 = 14 (C H )
Sat 6 14
H = 10
actual
DoU = 2
Two double bonds?

or triple bond?

or two rings

or ring and double bond

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EExxaammpplleess
C H N C H NBr
7 13 8 8 3
HH = 22((77)) ++ 22 ++ 11 = 1177
HH == 22((88))++22 ++ 11 - 33 == 1166
satt
sat
H = 13
actual H = 8
actual
DoU = 2
DoU = 4
Two double bonds?

FFour ddoubblle bbondds??

or triple bond?

two triple bonds?

or two rings

two rings/two
or ring and double 

bond double bonds?
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AAllkkeennee NNoommeennccllaattuurree
 Identify longest chain containing the alkene (both carbons)
 Number carbons in chain so that double bond carbons have
lloowweesstt ppoossssiibbllee nnuummbbeerrss ((iiff cchhooiiccee, ggiivvee ssuubb lloowweesstt nnuummbbeerr))
 Name, number, and list substituents alphabetically as prefix like
alkane nomenclature
 Indicate position of alkene with number-followed by name of
longest chain with suffix -ane replaced with -ene
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AAllkkeennee NNoommeennccllaattuurree:: IIssoommeerr PPrreeffiixx
 DDiissuubbssttiittuutteedd AAllkkeenneess:: CCiiss aanndd TTrraannss
 E and Z System
 rank two groups on each individual carbon by atomic number
 if same, find first point of difference
 count multiple bonds multiple times
 Highest Priority Groups same side = Z, opposite = E
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CCyyccllooaallkkeennee NNoommeennccllaattuurree
 Alkene carbons by definition carbons 1 and 2. Give first
substituent lowest possible number.
 NNaammee, nnuummbbeerr, aanndd lliisstt ssuubbssttiittuueennttss aallpphhaabbeettiiccaallllyy aass pprreeffiixx lliikkee
alkane nomenclature
 You do not need to indicate position of alkene with number,
simply name ring size with prefix cyclo and followed suffix -ene
 For rings smaller the cyclooctene you do not need to include
aallkkeennee ggeeoommeettrryy ((oonnllyy cciiss iiss ppoossssiibbllee))
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AAllkkeenneess aass SSuubbssttiittuueennttss
 Methylene
 VViinnyyll
 Allyl
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SSttaabbiilliittyy ooff AAllkkeenneess
 Evaluate heat given off when C=C is converted to C-C
 More stable alkene gives off less heat
ttrraannss-BBuutteennee ggeenneerraatteess 44 kkJJ lleessss hheeaatt tthhaann cciiss-bbuutteennee

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