chemistry 2100 chapter 12. alkynes and alkenes alkene (olefins): c n h 2n alkyne (acetylenes): c n h...
TRANSCRIPT
Chemistry 2100
Chapter 12
Alkynes and Alkenesalkene (olefins): CnH2n
alkyne (acetylenes): CnH2n-2 CC
H
HH
H HCCH
Ethene Ethyne
Ethylene Acetylene
Naming Alkenes and Alkynes• Parent name is that of the longest chain
that contains the C=C or C≡C.• Number the chain from the end that gives
the lower numbers to the carbons of the C=C or C≡C.
• Locate the C=C or C≡C by the number of its first carbon.
• Use -ene to show C=C, -yne for C≡C.• For cycloalkenes:
– Number ring carbons to give carbon 1 and 2 to the C=C bond.
– Because of this convention, no need to specify the number of the C=C.
CH2CCH3 CH
CH2
CH3
Br CH3 C C C CH3
CH3
CH3
Constitutional
IsomersStereoisomers
ConformationalIsomers
GeometricIsomers
Enantiomers Diastereomers
single bond rotation
chiral achiral
sameconnections
differentconnections
notmirrorimages
mirrorimages
Isomers
Alkene Isomerism
C=CH3C
H H
HC=C
H3C
H CH3
Htrans-2-Butene
mp -106°C, bp 1°Ccis-2-Butene
mp -139°C, bp 4°C C C
H H
CH3 CH3
C C
CH3 H
H CH3
CH3CH2
CH3CH2
3-methyl-cis-2-pentene3-methyl-trans-2-pentene
2-methyl-2-pentene
C C
CH3 H
CH3 CH2CH3
Conjugation
-carotene
-carotene
[O]
-carotene
2
[O]
Vitamin A
CH2OH
Vitamin A
CH2OH
trans-retinal
[O]
CHO
Vitamin A
CH2OH
trans-retinal
[O]
CHO
Vitamin A
CH2OH
trans-retinal
[O]
CHO
Vitamin A
CH2OH
trans-retinal
11-cis-retinal
isomerization
CHO
[O]
CHO
Vitamin A
CH2OH
C O
H
H2N
opsin
C O
H
H2N
opsin
C O
H
H2N
opsin
C O
H (- H2O)
H2N
rhodopsin
opsin
C O
H C N
H
(- H2O)
metarhodopsin
rhodopsin
C N
H
C
H
N
h
metarhodopsin
rhodopsin
C N
H
C
H
N
h
metarhodopsin
rhodopsin
C N
H
C
H
N
h
neuralimpulse
metarhodopsin
rhodopsin
C N
H
trans-retinal
11-cis-retinal
neural
impulse
metarhodopsin
C
H
N H2O
C
H
O
+
trans-retinal
11-cis-retinal
neural
impulse
metarhodopsin
C
H
N C
H
O
+
H2O
trans-retinal
11-cis-retinal
neural
impulse
metarhodopsin
C
H
N C
H
O
+
H2O
H2N
opsintrans-retinal
11-cis-retinal
neural
impulse
metarhodopsin
C
H
N C
H
O
+
H2O
H2N
opsintrans-retinal
11-cis-retinal
neural
impulse
metarhodopsin
C
H
N C
H
O
+
H2O
Terpenes – natural polyenes isoprene
(2-methyl-1,3-butadiene)
CH3
CHCCH2 CH2
limonene(orange, dill)
myrcene(bay)
geraniol(rose)
menthol(mint)
carvone(spearmint, dill)
OH
OH
O
zingiberene
(ginger)
-selinene(celery)
caryophyllene(cloves)
CH2PPOCH2 OPP +
squalene
squalene
O2
cholesterol
~25 steps
HO
lanosterol
HO
Making Alkenes B""A
B
CC
A
+CC
tetra tri di mono
CC
R
RR
R
>
'''
'''
CC
R
HR
R
>
'''
CC
H
HR
R
>
'
CC
H
HR
H
Reactions of Alkenes C C
BA
+ BACC
Hydrogenation
(cis or trans)
CH3
CH3 CH CH2CH3 CH3CH CHCH2CH3 Pt
H2 CH3CH2 CH2CH2CH3
CH3
CCH2 CH2CH3
CH3
CHCH 3CCH3orPt
H2
Partially Hydrogenated Vegetable Oil
"partially hydrogenated vegetable oil"
+
COOH
COOH
COOH
H2 catalyst
• •
Halogenation C C
H
+ Br2 C C
Br
BrH+
CH2Cl2
RT
∆ / h
C C
BrBr
Br2CC +
CH2Cl2
Cl2
Cl
Cl
CH3CH3
Acid Addition
CH2Cl2
H ClCHCH3CH3CH + CHCH3
Cl
CH3CH
H
CH3CH
Cl
CHCH3
H
minor major
H BrCH2CH3CH2CH + +CH2CH3CH2CH
BrH
CH2CH3CH2CH
HBr
H2SO4
H2SO4
H OH CH3 CH2 OHCH2 CH2 +
CH2 + H OHCH3
OH
Addition of HXAddition of HX (HCl, HBr, or HI) to an alkene gives a haloalkane.– H adds to one carbon of the C=C and X to the
other.
– Reaction is regioselective. One direction of bond forming (or bond breaking) occurs in preference to all other directions.
– Markovnikov’s rule: H adds to the less substituted carbon and X to the more substituted carbon.
37
Common Mechanism Steps
Pattern 1: Add a proton An acid is a proton donor and a base is a proton
acceptor. We can use curved arrows to show how a proton transfer occurs.
Patterns 2: Take a proton away. If we run the above reaction, in reverse it
corresponds to taking a proton away.
38
Common Mechanism Steps• Pattern 3: Reaction of an electrophile and a
nucleophile to form a new covalent bond.
• An electrophile is an electron-poor species that can accept a pair of electrons to form a new covalent bond.
• A nucleophile is an electron-rich species that can donate a pair of electrons to form a new covalent bond.
39
Common Mechanism Steps• Pattern 4: Reaction of a proton donor with a carbon-
carbon double bond to form a new covalent bond. The double bond provides both of the electrons that forms the new covalent bond. In the following reaction we show the hydronium ion as the proton donor.
• While the above equation is the most accurate way to show the proton transfer, we will simplify the equation to just show the proton and formation of the new covalent bond.
40
Addition of HCl to 2-Butene
Step 1: Add a proton – Reaction of the carbon-carbon double bond with H+
gives a secondary (2°) carbocation intermediate, a species containing a carbon atom with only three bonds to it and bearing a positive charge.
Step 2: Reaction of an electrophile and a nucleophile to form a new carbon-carbon bond.– Reaction of the carbocation intermediate with chloride
ion completes the addition.
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Polymerization
Z = CH3 polypropylene
Z = Cl PVC
Z = CN polyacrylonitrile
Z = OH polyvinyl alcohol
polypropylene
PVC
polyacrylonitrile
polyvinyl alcohol
CH2 CH
Z
n CH2CHCH2CHCH2CH CH2CH
Z Z Z Z
Polymerization– Show the structure of a polymer by placing
parentheses around the repeating monomer unit.– Place a subscript, n, outside the parentheses to
indicate that this unit repeats n times.– The structure of a polymer chain can be
reproduced by repeating the enclosed structure in both directions.
– The following is a section of polypropene (polypropylene).
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Polymers & Health
Pthalate, plasticizer
Bisphenol A = hard shell plastic