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.

41

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).

43

Polymers & Health

Pthalate, plasticizer

Bisphenol A = hard shell plastic