12-1 principles and applications of inorganic, organic, and biological chemistry denniston, topping,...
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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
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