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Chapter 9
Organic Chemistry II
Alkanes
Formulas
CH4
C2H6
C3H8
C4H10
C5H12
Name
methane
ethane
propane
butane
pentane
Formulas
C6H14
C7H16
C8H18
C9H20
C10H22
Name
hexane
heptane
octane
nonane
decane
1. The parent name is that of the longest continuous chain of C atoms.
2. An alkane minus one H atom is named as an alkyl group.
3. Indicate the locations where replacements are made.
Number in the direction that gives the smaller numbers for
the locations of the branches.
4. Use prefixes when there is more
than one alkyl branches of the same
kind & for other types of substituents.
5. Cyclic Alkanes — indicates by
cyclo before the hydrocarbon name.
Alkenes
• Alkenes, containing at least one carbon-carbon double bond, are
unsaturated hydrocarbons (olefin) and have the general formula CnH2n
where n = 1, 2, 3,…
• Cis- and Trans- Isomerism: because of the -bonding, there is not free
rotation about the double bond. Therefore, the following isomers are
possible:
two Cl 's are on
the same side of
the double bond
Cl
Cl
C
H
Cl
C
H
C
H
cis-dichloroethylene
two Cl 's are on
opposite side of
the double bond
C
H
Cl
trans-dichloroethylene
• Nomenclature:
1. Drop ane and add ene
CH2=CH2
ethene (ethylene)
CH2=CHCH2CH3
1-butene
CH3CH=CH2
propene
CH3CH=CHCH3
2-butene
Alkenes
2. In naming branched chain alkenes, 1) the longest continuous chain must
contain the double bond; 2) the double bond is given the lowest number.
CH3
5
CH3
1
CH
2
CH2
3
CH
4
CH2
CH3
CH3
4,5-dimethyl-2-hexene
CH2
CH
CH
1
2
3
CH2
C
CH
2
3
CH2
4
1,3-butadiene
CH3
1,2-butadiene
6
1
4
3. Polyenes (have several double bonds): use prefixes to denote the number
of double bonds and number the longest continuous chain to locate them.
4. Cyclic Olefins: use prefix cyclo and number to locate double bonds or
radicals on the ring.
cyclohexene 1,3-cyclohexadiene
3-methylcyclohexene
3,6-dimethyl-1,4cyclohexadiene
Alkynes
• Alkynes, containing at least one carbon-carbon triple bond, have the
general formula CnH2n-2 where n = 1, 2, 3,…
• Nomenclature: alkynes end in yne. Rules of nomenclature are the same as
for alkenes. (Note: alkyl means any of a series of univalent groups of the
general formula CnH2n+1 derived from aliphatic hydrocarbons)
CH≡CH
ethyne (acetylene)
CH≡CCH2CH3
1-butyne
CH3C≡CH2
propyne
CH3C≡CCH3
2-butyne
• Cyclic Alkynes and Polyalkynes:
1. The linear nature of the -C≡C- group  small ring alkynes are not stable.
2. Since the −C ≡ C− group is very reactive, poly-ynes are not common.
CH3
CH3
1
C
C
2
3
CH2
4
C
CH3
6
5
CH3
5,5-dimethyl-2-hexyne
CH3
1
C
C
C
C
2
3
4
5
CH2
6
2,4-heptadiyne
CH3
7
Aromatic Hydrocarbons
• An aromatic hydrocarbon is a hydrocarbon of which the molecular
structure incorporates one or more planar sets of six carbon atoms that are
connected by delocalized electrons.
• The term aromatic was assigned before the physical mechanism
determining aromaticity was discovered, and was derived from the fact that
many of the compounds have a sweet scent.
CH2CH3
ethylbenzene
Cl
NH2
chlorobenzene aminobenzene
6
2
5
3
4
benzene
nitrobenzene
toluene
furan
Br
Br
1
NO2
Br
1,2-dibromobenzene
Br
1,3-dibromobenzene
pyridine
imidazole
Aryl Groups
phenyl (C6H5-)
benzyl (C6H5CH2-)
R-pyridium
Polycyclic Aromatic Hydrocarbons
1-R1-3-R2-imidazolium
Reactions of Hydrocarbons
• Alkanes
1. Quite unreactive; used as nonpolar solvents.
2. Reactions involve the substitution of some other element for H.
3. Burned as fuel.
light
Substitution CH4(g) + Cl2(g)
CH3Cl(g) + HCl (g)
Combustion CH4(g) + 2O2(g)
CO2(g) + 2H2O(l) DH = -890.4 kJ
• Alkenes and Alkynes
1. Addition reactions: add small molecules across the multiple bonds. The 
bond breaks and two s bonds are formed.
2. If small molecules of HX are added to an unsymmetric alkene or alkyne,
the addition is such that the H goes to the C having the greater # of H's.
Addition CH
CH(g) + HBr(g)
Addition CH2
CHBr(g) + HBr(g)
CH2
CHBr(g)
CH3CHBr2(g)
3. Cracking
Pt
C2H6(g) catalyst
CH2
CH2(g) + H2(g)
4. Hydrogenation
CH
CH(g) + H2(g)
CH2
CH2(g)
• Aromatic compounds
1. Aromatic compounds undergo substitution rather than addition reactions.
2. Benzene and derivatives convert to cyclohexane and derivatives when
treated with H2 at 450 K and 10 atm with a finely divided nickel catalyst.
3. Bz is an excellent ligand in organometallic chemistry of low-valent metals,
e.g. the sandwich Cr(C6H6)2 and half-sandwich [RuCl2(C6H6)]2 complexes
H
CH2CH3
H
H
+ CH3CH2Cl
H
H
H
H
H
AlCl3
catalyst
+ HCl
H
H
H
Functional Groups
• Functional group compounds: Replace a H on a hydrocarbon with a
group of atoms other than C and H. Such groups are called functional
groups. They impart the specific chemical reactivity to the compound.
Organic Halides
• Organic Halide: halogen replaces a hydrogen on an alkane.
• Name halogen as a radical: a) Drop the elemental ending on the
halogen and add o, i.e. -F = fluoro, -Cl = chloro, -Br = bromo, -I =
iodo; b) halogen is given the lowest possible number.
CH3Cl
chloromethane (methyl chloride)
CH2Cl2 dichloromethane (methylene chloride)
CHCl3 trichloromethane (chloroform)
CCl4 tetrachloromethane (carbon tetrachloride)
CH3
1
I
CH3
CH
CH
2
3
CH3
4
2-iodo-3-methylbutane
Br
1,2dibromobenzene
Br
Organic Halides
• Use:
1. Starting materials for other organic compounds because the
halogen group is fairly easy to remove.
2. Solvents. however the use of halogenated solvents is being phased
out because of environmental concerns.
Chloroform is a common solvent in the laboratory because it is relatively
unreactive, miscible with most organic liquids, and conveniently volatile. It
is used as a solvent in the pharmaceutical industry and for producing dyes
and pesticides.
3. Coolants (CCl2F2 = Freon). The widespread use of chlorofluorocarbons is now thought to be one of the major causes for decrease in
the ozone layer.
Carbon tetrachloride is a reagent in synthetic chemistry and was formerly
widely used in fire extinguishers, as a precursor to refrigerants, and as a
cleaning agent. It is a colourless liquid with a "sweet" smell that can be
detected at low levels.
Alcohols
• Alcohol is formed by replacing a H on an alkane by an OH group. General
formula is R-OH where R = hydrocarbon fragment.
1,2-ethanediol
1, 2, 3 - propanetriol
glycerol or glycerine
• Nomenclature: a) the parent name is taken from the l.c.c. having the OH; b)
drop the e on the alkane name and add ol; c) When necessary, number the
l.c.c. to locate the OH.
OH
4-methyl-2-pentanol
CH3
CH
CH3
CH2 CH
CH3
Classification of Alcohols
• Primary Alcohols: OH is on a C that is bonded to at least two H's. That is,
the OH is on an end carbon. Examples: CH3OH, CH3CH2OH
• Secondary Alcohols: OH is on a C that is bonded to one H. That is, the C is
bonded to two other carbons. Examples: CH3CH(OH)CH3 isopropanol
• Tertiary Alcohols: OH is on a C that is not bonded to a H. That is, the C is
bonded to three other carbons..
Examples: CH3C(CH3)(OH)CH3 2-methyl-2-propanol (t-butyl alcohol)
Production of Ethanol
Biological C6H12O6(aq)
enzyme
2CH3CH2OH(aq) + 2CO2(g)
Commercial CH2=CH2(g) + H2O(g) H2SO4 CH3CH2OH(g)
Metabolic Oxidation of Ethanol
CH3CH2OH
alcohol
dehydrogenase
CH3CHO + H2
Ethers
• An Ether is an organic compound that contains an ether group – an O- atom connected to two alkyl or aryl groups – of general formula
R–O–R’.
H2SO4
CH3OH + HOCH3 catalyst CH3OCH3 + H2O
• Nomenclature: the name for simple ethers with no or few other functional
groups are a composite of the two substituents followed by ‘ether’. For
example, CH3OC2H5 methyl ethyl ether, C6H5OC6H5 diphenylether.
• CH3O- = methoxide ion; CH3O- = methoxyl group
• Used as solvents and anaesthetics
• Highly flammable and toxic
• Peroxide formation: ethers with a CH group
next to the ether O form peroxides. The reaction
requires oxygen (or air) and is accelerated by
light, metal catalysts and aldehydes. The resulting
peroxides can be explosive.
Important Ethers
Ethelene oxide
The smallest cyclic ether
Dimethyl ether
An aerosol spay propellant
Diethyl ether
A common low boiling solvent (34.6oC),
and an early anaesthetic
Dimethoxyethane A high boiling solvent (85oC)
Dioxane
A cyclic ether and high boiling solvent
(101oC)
Tetrahydrofuran
A cyclic ether, one of the most polar
simple ethers that is used as a solvent
Anisole
An aryl ether and a major constituent of
(methoxybenzene) the essential oil of anise seed
Crown ethers
Cyclic polyether that used as phase
transfer catalysts.
Polyethylene
glycol
A linear polyether, e.g. used in cosmetics
and pharmaceuticals