LECTURE № 2
Reactionary ability of the saturated hydrocarbons
(alkanes, cycloalkanes).
Reactionary ability of the unsaturated
hydrocarbons (alkenes, alkadienes, alkynes).
associate. prof. Ye. B. Dmukhalska, assistant. I.I. Medvid
Outline
1.
Alkanes. A Structure, a Nomenclature, the isomery of alkanes, the
methods preparation of alkanes
2. Physical and Chemical properties of alkanes
3. Cycloalkanes: Structure, Nomenclature, Conformation, the methods
of preparation of cycloalkanes.
4. Chemical properties of cycloalkanes.
5. Alkenes: a nomenclature, an isomery, the methods of prepartion of
alkenes.
6. Physical, Chemical properties of alkenes.
7. The dienes: nomenclature , configuration , isomers, the methods of
prepartion of dienes.
8. Chemical properties of dienes.
9. The nomenclature and isomery, a methods of prepartion of alkynes.
10. Physical, Chemical properties of alkynes.
Alkanes are the hydrocarbons of aliphatic row. Alkanes are
hydrocarbons in which all bonds are single covalent bonds
(-bonds). Alkanes are called saturated hydrocarbons.
Alkanes have the general
molecular formula CnH2n+2.
The simplest one, methane
(CH4), is also the most
abundant. Large amounts are
present in our atmosphere, in
the ground, and in the oceans.
Methane has been found on
Jupiter, Saturn, Uranus,
Neptune, and Pluto, and even
on Halley's Comet.
Alkanes:
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Undecane
Dodecane
Tridecane
Tetradecane
Pentadecane
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
C11H24
C12H26
C13H28
C14H30
C15H32
n-nonane
Some alkanes have trivial names. Methane, ethane, propane, n-butane,
isobutane, n-pentane, isopentane, and neopentane are trivial names.
Other alkanes have IUPAC names in which the number of carbon
atoms in the chain is specified by a Latin or Greek prefix preceding the
suffix -ane, which identifies the compound as a member of the alkane
family.
IUPAC Names of Unbranched Alkanes
4-ethyl-3-methyloctane
1. To chose the longest Carbon chain in the molecule.
2. To identify the substituent groups attached to the parent chain.
If in molecule there are two and more similar substituents
on the equal distance from the ends of the longest chain, it
is necessary to begin the numbering from the end of
Carbon chain where there are more substituents.
The main natural sources of alkanes are petroleum and gas. Petroleum is the
complex mixture of organic compounds; the main components of petroleum are
branched and normal alkanes. Gas consists of gaseous alkanes — methane
(95%), ethane, propane, butane. For receiving alkanes from petroleum it is
necessary to use fractional distillation. As the result several fractions are
received:
Fraction
Boiling
temperature, C
Alkanes mixture (number
of Carbon atoms)
Petroleum
ether
20-60
C5, C6
Benzine
60-180
C6 -C10
Kerosene
180-230
C11, C12
Diesel fuel
230-300
C13 - C17
Black oil
More than 300
C18 and more
This table lists that each fraction is the mixture of hydrocarbons which have
equal points of boiling temperature. Gas is shared to its components by
fractional distillation too.
1. Hydration of carbon (II) oxide. The mixture of CO and H2 is
heated at temperature 180-300C. In this reaction catalysts are Fe
and Co). As the result the mixture of n-alkanes appears.
This method is often used in industry for receiving of artificial benzine.
4. Allowing of salts of carboxylic acids and alkalis.
In normal conditions alkanes do not react with
acids and alkalis because -bonds in their molecules
are very strong. But alkanes take part in such
reactions as:
-reactions of the substitution;
-reactions of the oxidation;
-reactions of the destruction.
1. Halogenation of alkanes. Alkanes react with
halogens (except I2).
Alkanes can burn if oxygen is present. As the result H2O
and CO2 appear.
CH4 + 2O2 → CO2 + 2H2O
Cracking is the destroying of some −C−C− and −C−H
bonds in the molecule of alkanes at high
temperature: CH −CH → CH =CH + H
3
3
2
2
2
CH3−CH2−CH2−CH3 → CH4 + CH2=CH−CH3
→ CH3−CH3 + CH2=CH2
Cycloalkanes are hydrocarbons in which all Carbon
atoms form the cycle and are in the state of sp3hybridization. Cycloalkanes are saturated
hydrocarbons. Cycloalkanes have the general
molecular formula CnH2n.
spiranic system
bridge system
condensed system
Cycloalkanes are almost always written as skeletal
structures. Skeletal structures show the carbon–carbon
bonds as lines, but do not show the carbons or the
hydrogens bonded to carbons. Atoms other than carbon
and hydrogens bonded to atoms other than carbon are
shown. Each vertex in a skeletal structure represents a
carbon. It is understood that each carbon is bonded to the
appropriate number of hydrogens to give the carbon four
bonds.
The cyclic compounds most commonly found in nature contain
sixmembered rings because such rings can exist in a
conformation that is almost completely free of strain. This
conformation is called the chair conformation. In the chair
conformer of cyclohexane, all the bond angles are 111°, which is
very close to the ideal tetrahedral bond angle of 109.5°, and all
the adjacent bonds are staggered.
Cyclohexane can also exist in a boat conformation. Like the chair
conformer, the boat conformer is free of angle strain. However,
the boat conformer is not as stable as the chair conformer
because some of the bonds in the boat conformer are eclipsed,
giving it torsional strain. The boat conformer is further
destabilized by the close proximity of the flagpole hydrogens (the
hydrogens at the “bow” and “stern” of the boat), which causes
steric strain.
Unlike cyclohexane, which has two equivalent chair
conformers, the two chair conformers of a
monosubstituted cyclohexane such as
methylcyclohexane are not equivalent. The methyl
substituent is in an equatorial position in one
conformer and in an axial position in the other,
because substituents that are equatorial in one chair
conformer are axial in the other.
2. Dry distillation of calcium and barium salts of dicarboxylic acids.
1. The reaction of α,ω-dihalogenalkanes and metallic
sodium or zinc.
CH2 CH2 Br
+ Zn
CH2 CH2 Br
H2C
CH2
H2C
CH2
O
H2C
CH2 C
O
Ca
O
H2C H2C
C
-CaCO3
H2C
H3C
H2
C
C
C
H2
cyclopentanon
O
O
[H]
H2C
H3C
H2
C
CH2
C
H2
cyclopentane
+ ZnBr2
3. The reactions of cyclojoining:
a) The reaction of alkenes and carbenes:
H2
C
H3C
CH
CH2 +
H3C
CH2
C
H
propene
CH2
methylcyclopropane
b) Dimerization CH2
CH2
H2C
CH2
CH2
H3C
CH2
+
CH2
c) Diene synthesis
HC
CH2
CH2
+ H2
+
HC
CH2
CH2
cyclohexene
butadiene-1,3
H
C
H
C
d) Electrocyclic reactions
cyclohexane
CH
CH2
CH
CH
CH2
CH
CH
[H]
(Z)
CH
C
H
C
H
1,3,5-hexatriene
cyclohexadiene
cyclohexane
1. The reactions of substitution (halogenation)
hυ
+ Cl2
Cl
cyclopropane
+ HCl
chlorcyclopropane
2. The reactions of joining. During these
reactions −C−C− bonds are broken.
H2C
H3C
CH2
CH2
+ H2
Ni (Pt), t
H3C
CH2
+ H2
3000
Pt
CH3
butane
3000
cyclobutane
CH2
H3C
CH2 CH2 CH2 CH3
t
+ X2
X
CH2 CH2 CH2 X (äå Õ - Br, I)
h
Cl
+ 2Cl2
+2HCl
Cl
Br CH2 CH2 CH2 CH2 Br
+ Br2
Br
t0
+ Br2
+ HBr
Cl
t0
+ Cl2
+ HCl
+ HBr
+ HI
CH3 CH2 CH2 Br
CH3 CH2 CH2 CH2 I
[O]
OH
O2
C
-H2O
Cyclohexane
Cyclohexanol
O
2O2
HOOC
Cyclohexanol
(CH2)4 COOH
Adipinic acid
3. The reaction of increase and reduction
of Carbon cycle.
CH2 CH3
AlCl3, t
CH3
ethylcyclobutane
methylcyclopentane
The nomenclature of alkenes
The systematic (IUPAC) name of an alkene is obtained by replacing
the “ane” ending of the corresponding alkane with “ene.” For
example, a two-carbon alkene is called ethene and a three-carbon
alkene is called propene.
If the same number for the alkene functional
group suffix is obtained in both directions,
the correct name is the name that contains
the lowest substituent number.
Two groups containing a
carbon–carbon double
bond are used in
common names — the
vinyl group and the
allyl group.
The vinyl group is the smallest possible group that
contains a vinylic carbon; the allyl group is the smallest
possible group that contains an allylic carbon. When
“allyl” is used in nomenclature, the substituent must be
attached to the allylic carbon.
The isomery of alkenes
Although ethylene is the only two-carbon alkene, and
propene the only three-carbon alkene, there are four
isomeric alkenes of molecular formula C4H8:
1-butene, 2-methylpropene and 2-butene (cis- and
trans-)are structural isomers of butene. cis-2-butene
and trans-2-butene are geometrical isomers of butene.
When there are 3 or 4 different substituents near
2 carbon atoms connected by double bond, the
E,Z-system is used to name the compound.
CH2 CH3
H3C
C C
H3C H2C
CH2 CH2 CH3
Z-4-ethyl-3-methylheptene-3
H3C
H3C
H2C
C
C
CH2 CH2 CH3
CH2 CH3
E-4-ethyl-3-methylheptene-3
The methods of alkanes
preparation
Alkenes are in oil and gas in small amount. There are
methods of their extraction from oil and gas.
1. Dehydration of saturated alcohols
H2C
H
CH2
OH
ethanol
H2SO4,t
CH2 CH2 + H2O
ethylene
CH3
HC
H3C
C
CH3
CH3
H2SO4,t
H3C HC
OH H
C
CH3 + H2O
2-methylbutene-2
3-methylbutanol-2
2. Dehydrohalogenation of monohalogenalkanes
H3C
HC
H
CH2
NaOH
Br
H 3C
HC
CH2 + H2O + NaBr
propene
1-brompropane
3. Dehalogenation of dihalogenalkanes
H3C HC
Br
CH CH3
Br
2,3-dibrombutane
+ Zn
KOH
H3C HC
CH CH3 + ZnBr2
butene-2
4. Dehydrogenation of alkanes
CH3 CH2 CH3
Ni
CH2 CH
CH3 + H2
propene
propane
5. Hydrogenation of alkynes
CH C
CH3 + H2
Pt, Pd
CH2 CH
6. Dehydrogenation of alkanes
Ni
CH3 CH2 CH3
CH2 CH
propane
7. Hydrogenation of alkynes
CH C
CH3 + H2
Pt, Pd
CH3
CH3 + H2
propene
CH2 CH
CH3
Chemical properties of alkenes
Alkenes are very active, they can react with
many compounds, because of the presence of
double bond in their molecule.
I. Reactions of accession
1. Halogenation (the joining of halogens).
CH2 CH2 + Br2
CH2
CH2
Br
Br
2. Hydrohalogenation
CH2 CH2 + HBr
CH3
CH2
Br
bromomethane
This reaction runs by Markovnikov rule: the atom of Hydrogen
(from the molecule of hydrohalogen) joines to the atom of
Carbon which is connected by double bond and which is
connected with bigger amount of atoms of Hydrogen than
another carbon atom.
CH3
H3C
C
CH3
CH2 + HBr
CH3
C
Br
CH3
3. Joining of concentrated H2SO4
OSO3H
H3C
C
H
CH2 + H2SO4
CH3
C
H
CH3
4. Joining of water (hydration)
OH
H3C
C
H
CH2 + H2O
CH3
C
H
CH3
5. Joining of hypohalogenic acids
OH
H3C
C
H
CH2 + HClO
CH3
C
H
CH2
Cl
II. Reactions of reduction and oxidation
1. Reactions of reduction
H3C
C
H
CH2 + H2
Ni
CH3
H2
C CH3
2. Reactions of oxidation
•Reactions of oxidation by KMnO4
H2C
CH2 + 2KMnO4 + 4H2O
CH2
CH2
OH
OH
+ 2KOH + 2MnO2
•Reactions of oxidation by ozone
O
CH2 + O3
HC
H3C
O
CH
H3C
CH2
O
ozonide
•Reactions of oxidation by O2
2 H2C
Ag, t=300
CH2 + O2
ethylene
H2C
CH2
O
ethylenoxide
III. Reactions of polymerization
CH2═CH2 + CH2═CH2 + CH2═CH2 + … →
−CH2−CH2− + −CH2−CH2− + −CH2−CH2− + … →
−CH2−CH2−CH2−CH2−CH2−CH2− …
The nomenclature of dienes
Dienes are unsaturated hydrocarbons that contain two double
bonds. The general formula of dienes is C2H2n-2. There are 3 types
of location of double bonds in molecule.
The systematic (IUPAC) name of an dienes is obtained
by replacing the “ane” ending of the corresponding
alkane with “diene.”
Configurational isomers of dienes
A diene such as 1-chloro-2,4-heptadiene has four
configurational isomers because each of the double
bonds can have either the E or the Z configuration.
Thus, there are E-E, Z-Z, E-Z, and Z-E isomers.
The methods of dienes extraction
1. Dehydrogenation of alkanes and alkenes
H3C
CH2 CH2 CH3
Cr2O3, Al2O3, t=650
-2H2
H2C
CH CH
CH2
2. Dehydration of diols (alcohols with 2 –OH groups)
H2C
CH2 CH
OH
OH
CH3 Al O , t=280
2 3
-2H2O
H2C
CH CH
CH2
3. Dehydration of unsaturated alkohols
H3C
CH
CH CH2 OH
cat.
-H2O
H2C
CH CH
CH2
Chemical properties of dienes
1. Hydrogenation
H2C
CH CH
Ni,Pt
CH2 +H2
H3C
CH
CH CH3
2. Halogenation
Br
H2C
H2C
CH CH
Ni,Pt
CH2 +Br2
Br
CH CH CH2
Br
H2C
Br
CH CH
H3C
3. Hydrohalogenation
4. The Diels–Alder reaction
If a Diels–Alder reaction creates an acymmetric carbon in the
product, identical amounts of the R and S enantiomers will be
formed. In other words, the product will be a racemic mixture.
5. Polymerization
nCH2=CH−CH=CH2 → −(−CH2−CH=CH−CH2−)−n
The nomenclature and isomery of
alkynes
Alkynes are unsaturated hydrocarbons which
contain only one triple (−C≡C−) bond. They
conform to the general formula C2H2n-2, for one
triple bond. The IUPAC system for naming alkynes
employs the ending -yne instead of the -ane used
for naming of the corresponding saturated
hydrocarbons:
The numbering system for locating the triple bond
and substituent groups is analogous to that used for
the corresponding alkenes:
Both acetylene and ethyne are acceptable IUPAC
names for HC≡CH. The position of the triple bond
along the chain is specified by number in a manner
analogous to alkene nomenclature.
Hydrocarbons with more than one triple bond are
called alkadiynes, alkatriynes, and so on,
according to the number of triple bonds.
Hydrocarbons with both double and triple bonds
are called alkenynes (not alkynenes). The chain
always should be numbered to give the multiple
bonds the lowest possible numbers, and when
there is a choice, double bonds are given lower
numbers than triple bonds. For example,
The hydrocarbon substituents derived from
alkynes are called alkynyl groups:
Alkynes are characterized by structural isomery:
isomery of carbon chain and different location of
triple bond (isomery of location).
The methods of extraction of alkynes
1. Acetylene was first characterized by the French chemist P. E. M.
Berthelot in 1862 Calcium carbide is the calcium salt of the doubly negative
carbide ion
.
Carbide dianion is strongly basic and reacts with water to form
acetylene:
2. Dehydrogenation of alkenes:
3. Alkylation of acetylene:
HC
CH
NaNH2
HC
-NH3
CNa
C2H5Br
-NaBr
HC
4. Dehydrohalogenation of dihalogenalkanes and halogenalkenes
H
HC
Br
Br
CH
H
2NaOH, t
(C2H5OH)
HC
CH + 2NaBr + 2H2O
C
CH3
Chemical properties
I. The reactions of accession
1. Halogenation
2. Hydrohalogenation
3. Hydration
The reactions of substitution
1. The formation of acetylenides. Because of
their acidity alkynes can react like acids. In these
reactions the atoms of hydrogen are changed to
the atoms of metal.
HC≡CH + 2Ag(NH3)2OH → Ag−C≡C−Ag + 4NH3 + 2H2O
Silver acetylenide
2. The substitution of the atom of hydrogen in ≡C−H
–radical to atom of halogen:
CH3−CH≡C−H + Br2 → CH3−CH≡C−Br + HBr
The reactions of the oxidation and reduction
1. The oxidation of alkynes. In this reaction the
catalyst is KMnO4.
HC≡CH + 4[O] → HOOC−COOH
2. The reduction of alkynes.
3. The reactions of dimerisation, trimerisation and tetramerisation
2HC≡CH → HC≡C−CH=CH2
3HC≡CH →
vinilacetylene
Thank you for attention!