12-1

Principles and Applications ofInorganic, Organic, and Biological

ChemistryDenniston, Topping, and Caret

4th ed

Chapter 12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Power Point to Accompany

12.1 Alkenes and AlkynesAlkenes have one or more carbon-carbon

double bonds.Alkynes have one or more carbon-carbon

triple bonds.

Simplest alkene: ethene (ethylene) C2H4

Simplest alkyne: ethyne (acetylene) C2H2

C CH

H

H

HC CH H

bond anglesapproximately 120o

bond angles180o

12-3

Alkenes and AlkynesPhysical properties of the alkenes and

alkynes mirror those of alkanes. They are nonpolar and consequently are not soluble in water but highly soluble in nonpolar solvents.

Boiling points rise with molecular weight.

12.2 IUPAC NamesBase name from longest chain

containing the multiple bond.Change -ane to -ene or -yne.Number from the end that will give the

first carbon of the multiple bond the lower number.

Prefix the name with the number of the first multiple bond carbon.

Prefix branch/substituent names as for alkanes.

IUPAC Names-2

CH3CH CH2

CH3CH C

CH2CH3

CH2CH3Name

3-ethyl-6-methyl-3-heptene

Name CH3CHBr

C C CH2CH3

2-bromo-3-hexyne

Names-3Cyclic alkenes are named like cyclic

alkanes. Prefix name with cyclo.Numbering must start at one end of the

double bond and go through the bond.Substituents must have the lower

possible numbers.

5-chloro-3-methylcyclohexene

CH

CH2CH

CH

CHCH2Cl

CH3

Name:

12.3 Geometric Isomers, The pi Bond

sigma bond between carbons

Two p orbitals overlap side-by-side

pi bond has two lobes

C C C C

Geometric Isomers-cont.

2-butene is the first example of an alkene which can have two different structures - based on restricted rotation about the double bond.

C C

H

CH3

CH3

H

C C

CH3

H

CH3

Htrans-2-butene cis-2-butene

Identifying cis/trans IsomersIf one end of the C=C has two groups

the same, cis/trans isomers (geometric isomers) are not possible.

Both carbons of the C=C must have two different groups attached.

Find a group common to both ends of the C=C.If the common group is on the same

side of the pi bond, the molecule is cis; if on the opposite side , the molecule is trans.

Identifying cis/trans Isomers-2The common group (at each end) is the methyl group.

Both CH3s are on the same side of the pi bond.

cis-3-methyl-2-pentene

C CCH3

H

CH3

CH2CH3

Neither ene carbonhas two groups thesame.

Identifying cis/trans Isomers-3The common group is the chlorine atom.The chlorines are on opposite sides of the pi bond.

trans-1,2-dichloro-1-butene

C CCl

H

CH2

Cl

CH3

Quiz: cis/trans IsomersDecide whether each compound is cis, trans, or neither. Click to see the answers.

A: methyls are trans

B: No c/t. Right C has two isopropyls.

C: hydrogens are cis

C CCH3 CH

CH3

CH3CH3

H

C C

Cl

CH3

CH

CH

CH3

CH3

CH3

CH3

CCCH2CH2

H H

CH3CH3

AB

C

12-13

12.4 Alkenes in NatureAlkenes are abundant in nature.

Ethene is a fruit ripener and promotes plant growth.

Polyenes built from the isoprene skeleton are called isoprenoids.

The next slide shows some isoprenoids.

CH2 CCH3

CH CH2

12-14

Isoprenoids

CH2CCH3

CH CH2OHCH2CHCCH3

CH3

CH2

CH2CH CH2

CHCCH3

CCH3 CH2

CH2

CCH3

CHCH2OHCH2

CHC

CH2

CH3

CH2

CH CCH3

CH3

Geraniol (rose and geraniums)

Limonene (oil of lemon and orange)

Farnesol (Lily of the Valley)

12-15

12.5 Alkene ReactionsThere are two kinds of reactions typical

of alkenes:

Addition: two molecules combine to give one new molecule.

Redox: oxidation and reduction

The two classes are not always mutually exclusive.

12-16

Addition: General

A small molecule, AQ, reacts with the pi electrons of the double bond.

The pi bond breaks and its electrons are used to bond to the A and Q pieces.

Some additions require a catalyst.

+ AQ

CH3 CH CH CH3CH3 CH CH CH3

A Q

12-17

Reagents Adding to Alkenes

1. Symmetrical reagents:

H2 (Pt, Pd, or Ni as catalyst)

Br2, Cl2

2. Unsymmetrical reagents (acids)

HCl, HBr

H2O (requires strong acid catalyst

eg. H3O+, H2SO4, H3PO4)

3. Self addition or polymerization.

12-18

Symmetrical Reagents: Example

Note: the two hydrogens attach to each end of the double bond. There is no double bond in the product! The reaction is called hydrogenation.

CH3 CH CH2

CH3 CH CH2

H H

H2, Pt

CH3 CH2 CH3

or

12-19

Unsymmetrical Reagents: Example

Two products are possible depending how the reagent (as H and OH) adds to the ends of the pi bond.

CH3 CH CH2

CH3 CH CH2

OH H

H2O, H+

CH3 CH CH2

H OH

12-20

Markovnikov’s RuleDimitri Markovnikov (Russian)

observed many acid additions to C=C systems. He noticed that in all cases, the majority of the hydrogen went to a specific end of the double bond. He formulated his rule:

12-21

Markovnikov’s Rule-2When an acid (H-OH, H-Cl,

H-Br) adds to a double bond, the H of the acid usually goes to the end of the double bond with more hydrogens attached initially.

12-22

Major product: HCl + propene

major prdt.H goes to carbon withmore hydrogens

minor prdt.CH3CH CH2

+ HCl

CH3 CH2 CH2 Cl

CH3 CH CH3

Cl

12-23

Addition PolymersAlkene molecules add “head to tail”

using heat, pressure, and a catalyst.General

C CR

R

R

Rn C C

R

R

R

RCC

R

R

R

RC CR

R

R

RCC

R

R

R

R

C CR

R

R

R* *

n

etc.

12-24

Addition Polymers: ExamplesMonomer Polymer Name

CH2 CH

CHCl

CH2

CCH3

CH2CO O CH3

CF2CF2

CH2 CH* *n

CHCl

CH2* *n

CCH3

CH2CO O CH3

* *n

CF2CF2 ** n

Polystyrene

Polymethyl-methacrylateLucite

Polytetra-fluoroethyleneTeflonPolyvinyl Chloride (PVC)

12-25

Alkenes: ReductionAlkenes add two hydrogens to give

alkanes. We have already seen this reaction under symmetrical additions. Eg:

CH3 CH CH2

CH3 CH CH2

H H

H2, Pt

CH3 CH2 CH3

or

12-26

12.5 Aromatic HydrocarbonsBenzene’s structure was first proposed

by Kekule in the 1850s. He proposed a cyclic structure for benzene, C6H6.

Kekule realized that there was something special about benzene because, although his structures showed double bonds, the molecule did not react as if it had any unsaturation.

12-27

History-2The two equivalent structures proposed

by Kekule are recognized today as resonance structures. The real benzene molecule is a hybrid with each resonance structure contributing to the true structure.

CH

CHCH

CH

CHCH

CH

CHCH

CH

CHCH

12-28

Bonding in Benzene-Modern

The carbons in benzene are sp2 hybridized. Two sp2 orbitals are used to bond to other carbons and one to bond to hydrogen. The ring and all the hydrogens are coplanar. This describes the sigma bonding in the ring. (Picture on next slide.)

12-29

Sigma network on benzene

H

H

H

H

H

Hset of 3 sp2

hybrid orbitalson a carbon

C at centerof set

sp2-sp2

overlap

12-30

Pi bonding on benzene

The six p orbitals unused for the sp2

hybrids are perpendicular to the plane of the benzene ring. They overlap with one another to form the pi cloud, a ring of electrons above and below the ring.

The pi cloud electrons are free to move around the ring. They are said to be delocalized.

The next slide shows pi cloud formation.

12-31

Pi Cloud Formation in Benzene

Magenta lines=pi overlap

Insert Fig 12.7 to fill space

The current model of the bonding in benzene.

12-32

IUPAC Names: BenzenesCertain groups change the base name of

the ring system. E. g.

CH3

Toluene

OH

Phenol

NH2

Aniline

COOH

Benzoicacid

12-33

IUPAC Names: BenzenesFor monosubstituted benzenes, name

the group and add “benzene” (unless the group conveys a special name.)

Name:

Cl CH2 CH3

chlorobenzene ethylbenzene

NO2

nitrobenzene

12-34

IUPAC Names: Benzenes-2For disubstituted benzenes, name the

groups in alphabetical order. The first named group is at position 1.

If a “special group” is present, it must be number 1 on the ring.

An older system of naming uses ortho (o), meta (m), and para (p) to indicate groups that are 1,2, 1,3 and 1,4 on the ring.

12-35

IUPAC Names: Benzenes-3Name:

CH2 CH3

Br

CH3

NO2

ClCl

1-bromo-2-ethylbenzeneo-bromoethylbenzene

3-nitrotoluenem-nitrotoluene

1,4-dichlorobenzene or p-dichlorobenzene

12-36

IUPAC Names: Benzenes-4A final note:

When the benzene ring is a substituent on a chain (C6H5), it is called a phenyl

group. Note the difference between phenyl and phenol (a functional group).

CH CH3

CH2CH CH2

4-phenyl-1-pentene

12-37

Reactions of BenzeneBenzene undergos aromatic substitution

reactions: an atom or group substitutes for an H on the ring.

All benzene reactions (in our class) require a catalyst.

The reactions are:

1. Nitration

2. Halogenation

3. Sulfonation

12-38

Reactions of Benzene-1Nitration places the nitro group on the

ring. Sulfuric acid is needed as a catalyst.

+ HNO3

N

O

OH2SO4

+ H2O

12-39

Reactions of Benzene-2Halogenation places a Br or Cl on the

ring. Fe or FeCl3 are used as catalysts.

Cl+ Cl2

Fe

bromine may substitute for chlorine

12-40

Reactions of Benzene-3Sulfonation places an SO3H group on the

ring.

SO

OHOSO3

conc.H2SO4

+ H2O

+

12-41

Heterocyclic AromaticsRings with a hetero atom (typically O, N,

S) and delocalized electrons are also aromatic. Many have a six membered ring, some have a five membered ring. Eg:

N

N

NO S

pyridine pyrimidine furan thiophene

12-42

Heterocyclic Aromatics-cont.Heterocyclic aromatics are similar to

benzene in stability.

Many are significant biologically.

N

N

N

N

H

N

Npyrimidine purine

Found inDNA and RNA

NH

pyrrole

Found in hemoglobinand chlorophyll

12-43

THE END

Unsaturated

Hydrocarbons