Lec 2.new hydrocarbons. alkanes, alkenes,alkynes,alkadienes

transcript

Chapter 2:

(alkanes, alkenes, alkadienes, alkynes).

1. Concept of alkanes

2. Structure of alkanes

3. Nomenclature of alkanes

4. The isomers of alkanes

5. The methods of extraction of alkanes

6. Physical properties of alkanes

7. Chemical properties of alkanes

8. Structure of cycloalkanes

9. Nomenclature of cycloalkanes

10. The methods of extraction of cycloalkanes

11. Chemical properties of cycloalkanes

OutlineOutline

12. Concept of alkenes13. The nomenclature of alkenes13. The isomers of alkenes14. The methods of extraction of alkenes15. Physical properties of alkenes16. Chemical properties of alkenes17. The nomenclature of dienes21. The nomenclature and isomers of alkynes22. The nomenclature and isomers of alkynes23. Physical properties24. Chemical properties

• Alkanes are aliphatic hydrocarbons. Alkanes are called saturated hydrocarbons.

• the general molecular formula CnH2n+2.

• Methane has been found on Jupiter, Uranus, Neptune.

Alkanes can have either simple (unbranched) or branched Carbon chain. Alkanes with unbranched Carbon chain are called normal or n-alkanes.

n-nonane

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

1. To choose the longest Carbon chain in the molecule.

H3C CH

CH CH2

H3C CH3

the longest main chain(is the most branched,has 3 substituents)

H3C CH

CH CH2

H3C CH3

not the longest main chain(is not the most branched,has 2 substituents)

2. To identify the substituent groups attached to the parent chain.

H3C CH

CH2 CH2 CH31 2 3 4 5

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.

4-ethyl-3-methyloctane

C-C-C-C-C-C-C-C

CH3 CH2-CH3

4-ethyl-6-methyloctane(wrong)5-ethyl-3-methyloctane(correct)

Number the chain so that substituents take lowest possible number

N.B: Di, tri, tetra….are ignored in alphabetical order but iso, neo & cyclo are not ignored

There are the primary, the secondary, the tertiary and the quaternary carbon atoms.

1,2,3,4,5 – primary;6 – secondary;7 – tertiary;8 – quaternary.

H3C CH C

• Boiling point of alkanes increase with increasing the number of carbon atoms.• B.pt. decreases with branching.

FractionFraction Boiling Boiling temperature, temperature,

°°CC

Alkanes mixture (the Alkanes mixture (the number of Carbon number of Carbon

atoms)atoms)

Petroleum etherPetroleum ether 20-6020-60 CC55, C, C66

BenzineBenzine 60-18060-180 CC6 6 -C-C1010

KeroseneKerosene 180-230180-230 CC1111, C, C1212

Diesel fuel Diesel fuel 230-300230-300 CC13 13 - C- C1717

Black oilBlack oil More than 300More than 300 CC1818 and more and more

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. For receiving alkanes from petroleum it is necessary to use fractional distillation.

Fractional distillation of petroleum

Refinery gases: methane, ethane, propane, butene..

1. Hydrogenation 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.

CO 2H2Fe (Co)

H2O+ n-alkanes +Depending on metals used & reaction conditions mixture of alkanes, alkenes or alcohols are obtained.

H3C C C CH3 H2 H3C C C CH3

+butyne-2

Pt (Pd, Ni)

butene-2

H3C C C CH3

H2 H2CH2CH3C CH3+butane

Pt (Pd, Ni)

butene-2

H3C CH2 CO

ONaNaOH H3C CH3 Na2CO3+ +

H 2Na H3CH3C 2NaI+2

iodomethane

ethane

4. Reactions of salts of carboxylic acids and 4. Reactions of salts of carboxylic acids and alkalis.alkalis. (heat). (heat).

The first four alkanes are gaseous at room temperature. The unbranched alkanes pentane (C5H12) through heptadecane (C17H36) are liquids, whereas higher homologs are solids.

The boiling points of unbranched alkanes increase with the number of carbon atoms. Branched alkanes have lower boiling points than their unbranched isomers.

• Alkanes are isoluble in water but soluble in organic solvents.• Insolubility increase with increasing no of C.

• In normal conditions alkanes do not react with acids and alkalis because σ-bonds in their molecules are very strong. They undergo.

-reactions of the substitution;-reactions of the substitution;-reactions of the oxidation; -reactions of the oxidation; -reactions of the destruction. -reactions of the destruction.

CH4 Cl2 HCl H3C Cl+ +chlormethane

H3C Cl Cl2 HCl H2C Cl

+dichlormethane+

Cl Cl2 HCl C Cl

tetrachlormethane

H2C Cl

Cl2 HCl CH

trichlormethane

H3C CH2 CH3 SO2 Cl2 H3C CH2 CH2 SO2Cl HCl+ + +

Mixtures are obtained: 25% 1-nitropropane, 40% 2-nitroprpane, nitroethane 10%, nitromethane25%.The products can be seperated by fractional distillation.

Alkanes can burn if oxygen is present. As the result H2O and CO2 appear.

a. complete combustion.

CH4 + 2O2 → CO2 + 2H2O, exothermic rxn,

b. Incomplete combustion. Produces CO (stops oxygen transport in blood.

CH4 + 3/2O2 → CO+ 2H2O

Cycloalkanes are saturated hydrocarbons. Cycloalkanes have the general molecular formula CnH2n.

• 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.

• In the case of a cycloalkane with an attached alkyl

substituent, the ring is the parent hydrocarbon unless the

substituent has more carbon atoms than the ring. In that

case, the substituent is the parent hydrocarbon and the ring

is named as a substituent.

There is no need to number the position of a single substituent

on a ring.

• If the ring has two different substituents, they are cited in alphabetical order and the number 1 position is given to the substituent cited first.

petroleum contains such cycloalkanes as cyclopentane and cyclohexane.

1. The reaction of 1,4-dihaloalkanes and metallic sodium or zinc.

ZnBr2+ +

1. Concept of alkenes

Alkenes (Olefins) are unsaturated hydrocarbons which contain one carbon–carbon double bond.The general formula of acyclic alkenes is CnH2n. The general formula of cyclic alkenes is CnH2n-2.

Alkenes play many important roles in biology. Ethene, for example, is a plant hormone — a compound that controls the plant’s growth and other changes in its tissues. Ethene affects seed germination, flower maturation, and fruit ripening.

2. The nomenclature of alkenes

The systematic (IUPAC) name of an alkene is obtained by replacing the “ane” ending of the corresponding alkane with “ene.”

Most alkene names need a number to indicate the position of the double bond. The IUPAC rules:

1. The longest continuous chain containing the functional group (in this case, the carbon–carbon double bond) is numbered in a direction that gives the functional group suffix the lowest possible number.

2. The name of a substituent is cited before the name of the longest continuous chain containing the functional group.

3. If a chain has more than one substituent, the substituents are cited in alphabetical order. The prefixes di, tri, sec, and tert are ignored in alphabetizing, but iso, neo, and cyclo are not ignored.

4. 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.

5. In cyclic alkenes, a number is not needed to denote the position of the functional group, because the ring is always numbered so that the double bond is between carbons 1 and 2.

3. The isomers 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.

C CCH2

H2CH3C

CH2 CH3

Z-4-ethyl-3-methylheptene-3

C CCH2

H2CH3C

E-4-ethyl-3-methylheptene-3

4. The methods of extraction of alkenes

Alkenes are in oil and gas in small amount. There are methods of their extraction from oil and gas.

Artificial methods:1. Dehydration of saturated alcohols

H2C CH2

ethanol

H2SO4,tCH2 CH2

ethylene

When the molecule contain a long branched carbon chain, not all carbon-hydrogen bonds can be destroyed. If the atom of carbon is connected with only 1 hydrogen atom, it gives the hydrogen atom more easily than the carbon atom which is connected with 2 or 3 atoms of hydrogen. This rule is named Zajtsev rule.

3-methylbutanol-2

H2SO4,t HC C + H2OH3C

H3CCH3

CH3CH3

2-methylbutene-2

2. Dehydrohalogenation of monohalogenalkanes

HC CH2

H3CNaOH

HC CH2H3C H2O NaBr

1-brompropane

propene+ +

3. Dehalogenation of dihalogenalkanes

H3C CH3

HC CHH3C CH3 ZnBr2

2,3-dibrombutanebutene-2

4. Dehydrogenation of alkanes

CH3 CH2 CH3Ni CH2 CH CH3 H2+

propane propene

5. Hydrogenation of alkynes

CH C CH3 H2Pt, Pd

CH2 CH CH3+

5. Physical properties of alkenes

Alkenes resemble alkanes in most of their physical properties. • The lower molecular weight alkenes through C4H8 are gases at room temperature and atmospheric pressure.

•Alkenes which contain carbon atoms (C5 – C17) are liquids and alkenes with carbon chain (≥C18) are solids.

•All alkenes are not soluble in water but are soluble in some organic solvents.

•n-alkenes have higher boiling temperatures than their isomers with branched carbon chain.

6. 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 joining1. Halogenation (the joining of halogens).

CH2 CH2 Br2CH2 CH2

Br Br+

2. Hydrohalogenation

CH2 CH2 + HBr CH3 CH2 Brbromomethane

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.

C CH2 +HBr CH3 CH3C

II. Reactions of reduction and oxidation

1. Reactions of reduction

CH2H3C H2 CH3

H2C CH3+ Ni

2. Reactions of oxidation •Reactions of oxidation by KMnO4

H2C CH2 2KMnO4 4H2OCH2 CH2

2KOH 2MnO2+ + ++

7. 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.

8. The nomenclature and isomers 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

12. The nomenclature and isomers of alkynes

•The IUPAC system for naming alkynes employs the ending -yne instead of the -ane used for naming of the corresponding saturated hydrocarbon:

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.

14. Physical properties

The most distinctive aspect of the chemistry of acetylenes is their acidity. As a class, compounds of the type RC≡CH are the most acidic of all simple hydrocarbons.

In the homological row the first 3 alkynes (C2-C4) are

gases, alkynes with carbon chain C5-C15 are liquids and

next alkynes are solids.

15. Chemical properties

I. The reactions of joining1. Halogenation

2. Hydrohalogenation

3. Hydration

Lec 2.new hydrocarbons. alkanes, alkenes,alkynes,alkadienes

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