organic compounds
——hydrocarbons
The term "organic" appears to have been used for
the first time about 1777 and was applied to those
materials occurring in or derived from living
organisms,Accordingly,such substances as starch,
alcohol,and urea were classified as organic,for
starch is produced by living plants,alcohol is a
product of fermentation caused by
microorganisms,and urea is contained in urine,In
1824,however,the German chemist W?hler
synthesized urea,and the original meaning of the
term,organic” no longer applied,Organic
compounds,in the modern sense,are the
compounds of carbon,Many thousands of carbon
compounds which are not found in or derived
from living organisms have been produced by
chemists,and well over a million organic
compounds are already known,
The existence of so many organic compounds is due
primarily to the ability of carbon atoms to combine
with other carbon atoms,forming chains of different
lengths and rings of different sizes,The elements,
other than carbon,most frequently found in organic
compounds are hydrogen,oxygen,nitrogen,sulfur,
the halogens,phosphorus,and some of the metals.
Although the number of organic compounds is
vast,the study of organic chemistry is greatly
simplified by the fact that the chemistry of carbon
compounds can be organized around,functional
groups”,each of which imparts similarities in
chemical properties.
Hydrocarbons
The simplest organic compounds are those
containing only carbon and hydrogen,Such
compounds are known as hydrocarbon,Some
of them are found in nature,where they were
derived from plant or animal forms of life,
Several types of hydrocarbons are possible.
The alkanes
The series of compounds which have the general
empirical formula CnH2n+2,where n is an integer,is
called the alkane,or paraffin.
The lighter members of the alkane series are gases,the
members of intermediate weight are liquids,and the
heavier members are solids,From the formulas of the
compounds it is evident that each member differs from
the preceding one by the increment CH2,A series of
compounds in which each member differs from the one
before it by a common increment is called a homologous
series.
The electronic formulas for methane,
ethane,and propane are easily written,
Although the electronic formula
representation makes the molecules seem
planar,it must be remembered that in all
the alkanes the C— C and C— H bonds
have the geometrical arrangement set by
the tetrahedral configuration of each carbon
unit.
Methane
Pentane
There are two hydrocarbons having the formula
C4H10,and these are known as normal butane and
isobutane,The two butanes are isomers,They have
the same empirical formula,and hence the same
composition,but different physical and chemical
properties,because they differ in the arrangement of
the atoms in their molecules,Normal butane,n-
butane,is a,straight chain” molecule and isobutane
is a,branched chain” molecule,The number of
possible isomers increases with increasing molecular
weight; the hydrocarbon of large molecular weight
have great numbers of isomers.
Alkanes are characterized by being rather
unreactive chemically; hence,the use of the
name paraffin,which means,having little
affinity”,The following reaction is a typical
one for the alkanes and is referred to as a
substitution reaction,(heat or UV light)
CH4+Cl2=CH3Cl+HCl
This reaction is a chain reaction which proceeds
in several steps,An important point concerning
this particular reaction is that it transforms an
alkane molecule into one which has a more
reactive,functional group” on it——a halogen
in this specific case,The functional group makes
it possible for the molecule to take part in many
different kinds of reactions.
Another very important reaction of alkanes is
based upon their ability to burn in air in a
highly exothermic oxidation-reduction
reaction,A typical combustion reaction is that
for ethane.(2C2H6+O2=4CO2+6H2O)
Methane is the principal component of
natural gas,Gasoline is a mixture of straight
and branched chain alkanes containing 5~9
carbon atoms plus various additives,
Kerosene,diesel oil,and fuel oil are primarily
mixtures of alkanes with higher molecular
weights,
The alkenes
Hydrocarbon molecules which contain a
double bond are members of a second
homologous series,referred to as alkenes,The
two carbon atoms linked by a double bond are
bound together by two kinds of bonds,one
sigma C— C bond and one pi C— C bond.
The alkenes have the general empirical
formula CnH2n,ethylene,C2H4,the simplest
alkene,has a trigonal planar structure,The
second member of the series is propylene and
then come the butene isomers,The series
builds up in a manner analogous to the alkane
series.
In writing formulas for members of the ethylene
series,the two shared electron pairs are usually
represented by two lines.
Note that carbon atoms with single bonds have
sp3 hybridization,and those with double bonds
have sp2 hybridization,Actually,two isomers of
2-butene exist,because the double bond is quite
rigid and hence rotation about it is very difficult,
Writing the formulas for the butene molecules in
a slightly different fashion makes it possible to
show the three butene isomers more clearly.
Alkenes are much more reactive than alkanes,The π
bond,being a relatively weaker bond,is disrupted
much more easily than a σbond,Thus,the reactions
characteristic of alkenes are those in which the π
bond is broken.
In the presence of a suitable catalyst (Pt,Pd,or Ni,
for example),alkenes add hydrogen to form the
corresponding alkanes,
Chlorine breaks the double bond and adds to the
two carbons adjacent to the double bond in the
alkenes,instead of replacing a hydrogen as in the
alkanes,
Many other reagents react with alkenes by breaking
the double bond,An example is the acid-catalyzed
addition of water to an alkene.
A very important property of the alkenes is their
ability to add to themselves,This reaction is a very
significant one in the plastics industry.
Because ethylene and the other alkenes have the
ability to add chlorine and other atoms,they are
called unsaturated compounds,On the other hand,
ethane and the other alkanes react with chlorine by
substitution only,so they are called saturated
compounds.
Ethylene is a colorless gas with a rather sweet
odor,It occurs in natural gas and is formed
when coal or wood is submitted to destructive
distillation,Ethylene,mixed with oxygen,is
used as an anesthetic in dentistry and surgery,
It has the interesting property of causing
green fruits to ripen and is used commercially
for this purpose,The production of 11,790,000
tons of ethylene in 1974 made it fifth highest
of all chemicals produced in the United States
for that year,
The alkynes
Hydrocarbon molecules which contain the
triple bond are called alkynes; they make up
another series of unsaturated hydrocarbons,
Two carbon atoms joined by a triple bond are
bound together by one sigma C— C bond and
two pi C— C bonds,The alkynes have the
general empirical formula CnH2n-2.
The simplest and most important member of the
alkyne homologous series is acetylene,C2H2,The
electronic and line formulas for acetylene are
H:C:::C:H H-C≡C-H,
Acetylene is liberated when calcium carbide is
treated with water.
Chemically,the alkynes are similar to alkenes
except that with two π bonds they react even more
readily,adding twice as much reagent in addition
reactions,The reaction of acetylene with bromine is
a typical example.
Acetylene and all the other alkynes burn very
easily.
The triple bond is a high energy bond,and this
energy is released when the compound is
transformed into carbon dioxide and water,Thus,
the flame produced by burning acetylene is very hot;
it is used in welding and cutting metal,When
acetylene burns,some of it breaks down a second
way according to the equation C2H2→2C+H 2,At the
temperature of the flame,the particles of carbon
become heated to incandescence; i.e.,they give off a
brilliant luminous white light,At one time,acetylene
was used to light homes and in lamps for bicycles
and automobiles.
Cyclic hydrocarbons—benzene
It is possible to introduce three double bonds into the
cyclohexane ring,If this experiment is performed,it
is found that the compound which is formed has
unique chemical properties,not very much like an
alkene,We could call the product cyclohexatriene,
but it actually is named benzene,The empirical
formula is C6H6.
The unique properties of benzene are related to its
molecular orbital structure,As can be surmised from
the structural formula above,all the carbons in
benzene are sp2 hybridized,The three sp2 hybrid
orbitals lie in a plane,and hence the benzene
molecule is planar.
Benzene,a volatile liquid,is the first and best known
member of another homologous series in which each
member differs from its predecessor by the increment CH2,
Benzene and its homologs,which have one ring,have the
general formula CnH2n-6,Compounds of his series are in a
class called aromatic hydrocarbons,because many of them
have pleasant odors (though most are poisonous and
should be smelled gently,if at all).
If one hydrogen atom on each of two different carbon
atoms of benzene is replaced by a CH3 group,the product
is xylene,Thus,xylene may be thought of as a derivative of
benzene,Xylene has three isomers since substitutions to
introduce the two CH3 groups may be made in three
different relative positions on the ring; ortho-xylene,meta-
xylene and para-xylene.
There are many derivatives of benzene,The
hydrogen atoms can be replaced by many
different kinds of groups,The following are
typical examples,toluene,styrene and
bromobenzene.
Some of the important aromatic
hydrocarbons and their derivatives contain
more than one ring (polynuclear aromatic
hydrocarbons),Examples are naphthalene,
C10H8,familiarly known in moth balls;
anthracene,C14H10; and benzpyrene,C20H12,
The aromatic hydrocarbons are widely used
in the manufacture of dyes,synthetic drugs,
explosives,plastics,and many other
substances,For example,the important
explosive trinitrotoluene (TNT),
C6H2(CH3)(NO2)3,is synthesized from toluene
by replacing three hydrogen atoms with nitro-
groups,-NO2,
——hydrocarbons
The term "organic" appears to have been used for
the first time about 1777 and was applied to those
materials occurring in or derived from living
organisms,Accordingly,such substances as starch,
alcohol,and urea were classified as organic,for
starch is produced by living plants,alcohol is a
product of fermentation caused by
microorganisms,and urea is contained in urine,In
1824,however,the German chemist W?hler
synthesized urea,and the original meaning of the
term,organic” no longer applied,Organic
compounds,in the modern sense,are the
compounds of carbon,Many thousands of carbon
compounds which are not found in or derived
from living organisms have been produced by
chemists,and well over a million organic
compounds are already known,
The existence of so many organic compounds is due
primarily to the ability of carbon atoms to combine
with other carbon atoms,forming chains of different
lengths and rings of different sizes,The elements,
other than carbon,most frequently found in organic
compounds are hydrogen,oxygen,nitrogen,sulfur,
the halogens,phosphorus,and some of the metals.
Although the number of organic compounds is
vast,the study of organic chemistry is greatly
simplified by the fact that the chemistry of carbon
compounds can be organized around,functional
groups”,each of which imparts similarities in
chemical properties.
Hydrocarbons
The simplest organic compounds are those
containing only carbon and hydrogen,Such
compounds are known as hydrocarbon,Some
of them are found in nature,where they were
derived from plant or animal forms of life,
Several types of hydrocarbons are possible.
The alkanes
The series of compounds which have the general
empirical formula CnH2n+2,where n is an integer,is
called the alkane,or paraffin.
The lighter members of the alkane series are gases,the
members of intermediate weight are liquids,and the
heavier members are solids,From the formulas of the
compounds it is evident that each member differs from
the preceding one by the increment CH2,A series of
compounds in which each member differs from the one
before it by a common increment is called a homologous
series.
The electronic formulas for methane,
ethane,and propane are easily written,
Although the electronic formula
representation makes the molecules seem
planar,it must be remembered that in all
the alkanes the C— C and C— H bonds
have the geometrical arrangement set by
the tetrahedral configuration of each carbon
unit.
Methane
Pentane
There are two hydrocarbons having the formula
C4H10,and these are known as normal butane and
isobutane,The two butanes are isomers,They have
the same empirical formula,and hence the same
composition,but different physical and chemical
properties,because they differ in the arrangement of
the atoms in their molecules,Normal butane,n-
butane,is a,straight chain” molecule and isobutane
is a,branched chain” molecule,The number of
possible isomers increases with increasing molecular
weight; the hydrocarbon of large molecular weight
have great numbers of isomers.
Alkanes are characterized by being rather
unreactive chemically; hence,the use of the
name paraffin,which means,having little
affinity”,The following reaction is a typical
one for the alkanes and is referred to as a
substitution reaction,(heat or UV light)
CH4+Cl2=CH3Cl+HCl
This reaction is a chain reaction which proceeds
in several steps,An important point concerning
this particular reaction is that it transforms an
alkane molecule into one which has a more
reactive,functional group” on it——a halogen
in this specific case,The functional group makes
it possible for the molecule to take part in many
different kinds of reactions.
Another very important reaction of alkanes is
based upon their ability to burn in air in a
highly exothermic oxidation-reduction
reaction,A typical combustion reaction is that
for ethane.(2C2H6+O2=4CO2+6H2O)
Methane is the principal component of
natural gas,Gasoline is a mixture of straight
and branched chain alkanes containing 5~9
carbon atoms plus various additives,
Kerosene,diesel oil,and fuel oil are primarily
mixtures of alkanes with higher molecular
weights,
The alkenes
Hydrocarbon molecules which contain a
double bond are members of a second
homologous series,referred to as alkenes,The
two carbon atoms linked by a double bond are
bound together by two kinds of bonds,one
sigma C— C bond and one pi C— C bond.
The alkenes have the general empirical
formula CnH2n,ethylene,C2H4,the simplest
alkene,has a trigonal planar structure,The
second member of the series is propylene and
then come the butene isomers,The series
builds up in a manner analogous to the alkane
series.
In writing formulas for members of the ethylene
series,the two shared electron pairs are usually
represented by two lines.
Note that carbon atoms with single bonds have
sp3 hybridization,and those with double bonds
have sp2 hybridization,Actually,two isomers of
2-butene exist,because the double bond is quite
rigid and hence rotation about it is very difficult,
Writing the formulas for the butene molecules in
a slightly different fashion makes it possible to
show the three butene isomers more clearly.
Alkenes are much more reactive than alkanes,The π
bond,being a relatively weaker bond,is disrupted
much more easily than a σbond,Thus,the reactions
characteristic of alkenes are those in which the π
bond is broken.
In the presence of a suitable catalyst (Pt,Pd,or Ni,
for example),alkenes add hydrogen to form the
corresponding alkanes,
Chlorine breaks the double bond and adds to the
two carbons adjacent to the double bond in the
alkenes,instead of replacing a hydrogen as in the
alkanes,
Many other reagents react with alkenes by breaking
the double bond,An example is the acid-catalyzed
addition of water to an alkene.
A very important property of the alkenes is their
ability to add to themselves,This reaction is a very
significant one in the plastics industry.
Because ethylene and the other alkenes have the
ability to add chlorine and other atoms,they are
called unsaturated compounds,On the other hand,
ethane and the other alkanes react with chlorine by
substitution only,so they are called saturated
compounds.
Ethylene is a colorless gas with a rather sweet
odor,It occurs in natural gas and is formed
when coal or wood is submitted to destructive
distillation,Ethylene,mixed with oxygen,is
used as an anesthetic in dentistry and surgery,
It has the interesting property of causing
green fruits to ripen and is used commercially
for this purpose,The production of 11,790,000
tons of ethylene in 1974 made it fifth highest
of all chemicals produced in the United States
for that year,
The alkynes
Hydrocarbon molecules which contain the
triple bond are called alkynes; they make up
another series of unsaturated hydrocarbons,
Two carbon atoms joined by a triple bond are
bound together by one sigma C— C bond and
two pi C— C bonds,The alkynes have the
general empirical formula CnH2n-2.
The simplest and most important member of the
alkyne homologous series is acetylene,C2H2,The
electronic and line formulas for acetylene are
H:C:::C:H H-C≡C-H,
Acetylene is liberated when calcium carbide is
treated with water.
Chemically,the alkynes are similar to alkenes
except that with two π bonds they react even more
readily,adding twice as much reagent in addition
reactions,The reaction of acetylene with bromine is
a typical example.
Acetylene and all the other alkynes burn very
easily.
The triple bond is a high energy bond,and this
energy is released when the compound is
transformed into carbon dioxide and water,Thus,
the flame produced by burning acetylene is very hot;
it is used in welding and cutting metal,When
acetylene burns,some of it breaks down a second
way according to the equation C2H2→2C+H 2,At the
temperature of the flame,the particles of carbon
become heated to incandescence; i.e.,they give off a
brilliant luminous white light,At one time,acetylene
was used to light homes and in lamps for bicycles
and automobiles.
Cyclic hydrocarbons—benzene
It is possible to introduce three double bonds into the
cyclohexane ring,If this experiment is performed,it
is found that the compound which is formed has
unique chemical properties,not very much like an
alkene,We could call the product cyclohexatriene,
but it actually is named benzene,The empirical
formula is C6H6.
The unique properties of benzene are related to its
molecular orbital structure,As can be surmised from
the structural formula above,all the carbons in
benzene are sp2 hybridized,The three sp2 hybrid
orbitals lie in a plane,and hence the benzene
molecule is planar.
Benzene,a volatile liquid,is the first and best known
member of another homologous series in which each
member differs from its predecessor by the increment CH2,
Benzene and its homologs,which have one ring,have the
general formula CnH2n-6,Compounds of his series are in a
class called aromatic hydrocarbons,because many of them
have pleasant odors (though most are poisonous and
should be smelled gently,if at all).
If one hydrogen atom on each of two different carbon
atoms of benzene is replaced by a CH3 group,the product
is xylene,Thus,xylene may be thought of as a derivative of
benzene,Xylene has three isomers since substitutions to
introduce the two CH3 groups may be made in three
different relative positions on the ring; ortho-xylene,meta-
xylene and para-xylene.
There are many derivatives of benzene,The
hydrogen atoms can be replaced by many
different kinds of groups,The following are
typical examples,toluene,styrene and
bromobenzene.
Some of the important aromatic
hydrocarbons and their derivatives contain
more than one ring (polynuclear aromatic
hydrocarbons),Examples are naphthalene,
C10H8,familiarly known in moth balls;
anthracene,C14H10; and benzpyrene,C20H12,
The aromatic hydrocarbons are widely used
in the manufacture of dyes,synthetic drugs,
explosives,plastics,and many other
substances,For example,the important
explosive trinitrotoluene (TNT),
C6H2(CH3)(NO2)3,is synthesized from toluene
by replacing three hydrogen atoms with nitro-
groups,-NO2,
