alkana - website staff uistaff.ui.ac.id/system/files/users/tania.surya/material/alkana.pdf · the...

AlkanaAlkanaAlkanaAlkanaAlkanaAlkanaAlkanaAlkana

Dept Teknik KimiaFTUI

Dept Dept TeknikTeknik KimiaKimia

FTUIFTUI

CCnnHH22nn+2+2

HydrocarbonsHydrocarbonsHydrocarbons

AromaticAromaticAromaticAliphaticAliphaticAliphatic


AromaticAromaticAromaticAliphaticAliphaticAliphatic

AlkanaAlkanaAlkana AlkunaAlkunaAlkunaAlkenaAlkenaAlkena


AliphaticAliphaticAliphatic

AlkanaAlkanaAlkana

Alkanes are

hydrocarbons in which

all of the bonds are

single bonds.

CC CCHH HH

HH HH

HH HH

etana



AlkenaAlkenaAlkena

Alkenes are

hydrocarbons that

contain a carbon-carbon

double bond.

CC CC

HH HH

HH HH

Etena



AlkunaAlkunaAlkuna

Alkuna are

hydrocarbons that

contain a carbon-

carbon triple bond.

HCHC CHCH

Asetilen


AromaticAromaticAromatic

The most common

aromatic

hydrocarbons are

those that contain

a benzene ring.

HH

HH

HH

HH

HH

HH

StrukturStruktur alkanaalkana

� tetrahedral about carbon

� all bond angles are approximately 109.5°

PenggambaranPenggambaran AlkanaAlkana

CH3 CH2 CH2 CH3CH3 CH2 CH3 CH3CH2CH2 CH2 CH3

PentaneButanePropane PentanePropane

Structuralformula

Line-angleformula

Ball-and-stickmodel

PenamaanPenamaan AlkanaAlkana

� Suffix -anaana specifies an alkanaana

� Prefix tells the number of carbon atoms

undec-dodec-

tetradec-pentadec-hexadec-heptadec-

nonadec-eicos-

tridec-

11121314151617

octadec- 181920

Prefixmeth-eth-prop-but-pent-hex-

oct-non-dec-

1234567hept-89

10

Carbons CarbonsPrefix


�� Parent name:Parent name: the longest carbon chain

�� Substituent:Substituent: a group bonded to the parent

chain

�� alkyl group:alkyl group: given the symbol R-

Alkane Alkyl group

CH4

Name Name

Methane CH3 - Methyl group

CH3 CH3 Ethane CH3 CH2 - Ethyl group


� Each substituent is given a name and a number

� If there is one substituent, number the chain from the end that gives it the lower number

CH3 CHCH3

CH3

2-Methylpropane

12 3

2-metil propana

CH3 CH2 CH2 CHCH3

CH3

2-Methylpentane

123

45 5

432

1

(not 4-methylpentane)2-metil pentana


� If there are two or more identical substituents,

number the chain from the end that gives the

lower number to the substituent encountered

first

• indicate the number of times the

substituent appears by a prefix di-, tri-,

tetra-, etc.

• use commas to separate position numbers

2,4-Dimethylhexane1

23

45

66

54

32

1

(not 3,5-dimethylhexane)2,4-dimetil heksana


� If there are two or more different substituents,

• list them in alphabetical order

• number from the end of the chain that

gives the substituent encountered first the

lower number

3-Ethyl-5-methylheptane

12

34

5 67 7

65

43 2

1

(not 3-methyl-5-ethylheptane)3-etil-5-metil heptana


� The prefixes di-, tri-, tetra-, etc. are not

included in alphabetization

� alphabetize the names of substituents first and

then insert these prefixes

4-Ethyl-2,2-dimethylhexane(not 2,2-dimethyl-4-ethylhexane)

12 3

45

6

4-etil-2,2-dimetilheksana

Physical PropertiesPhysical Properties

� Boiling points: increase with increasing number of carbons

decrease with chain brainching

� Alkanes are non-polar, soluble in nonpolar or slightly polar

solvents, insoluble in water

� Intermolecular forces are van der Waals forces

� Less dense than water

Chemical PropertiesChemical Properties

� All alkanes burn in air to give CO2 and H2O

� Halogenation

� Pyrolysis (cracking): decomposition of a compound by

the action of heat alone

HalogenationHalogenation(mekanisme radikal bebas)

Alkanes can react with halogens to form alkyl halides

via free radical substitution pathways.

A radical is…………………………………………

HalogenationHalogenation(mekanisme radikal bebas)

Carbon radicals are formed by homolytic cleavage of

covalent bonds using either:

(1) Light ( hυ)

(2) Heat (∆)

(3) Radical Initiators (ROOR i.e. peroxides)

HalogenationHalogenation

The mechanism has

three distinct stages.

Stage I

Stage II

Stage III

Initiation( f ormation of the halogen radicals)

Propagation( f ormation of product and another

halogen radical)

Termination( multiple pathways to extinguish

all radicals)


Initiation:

The reaction begins with an initiation stage, which is the

separation of the halogen (X2) into two radicals (atoms with a

single unpaired electron) by the addition of uv light.

HalogenationHalogenationPropogation:

The initiation stage, or the formation of the chlorine radicals, is

immediately followed by the propogation stages--stages directly

involved in the formation of the product.

In the last stage, the tertiary radical then reacts with another

one of the chlorine molecules to form the product.

HalogenationHalogenationTermination:

Side reactions that can stop the chain reaction are called

termination stages.


monohalogenation

excess halogen is used

The most important steps of radical halogenation are those that lead to product formation—the propagation steps

Radical Reactions—Mechanism

Sources of AlkanesSources of Alkanes

� Natural gas

� 90-95% methane

� Petroleum

� gases (bp below 20°C)

� naphthas, including gasoline (bp 20 - 200°C)

� kerosene (bp 175 - 275°C)

� fuel oil (bp 250 - 400°C)

� lubricating oils (bp above 350°C)

� asphalt (residue after distillation)

� Coal

� Biomass ??????????

CycloalkanesCycloalkanes

� General formula CCnnHH2n2n

� five- and six-membered rings are the most common

� Structure and nomenclature

� to name, prefix the name of the corresponding open-chain alkane with cyclocyclo--,, and name each substituent on the ring

� if only one substituent, no need to give it a number

� if two substituents, number from the substituent of lower alphabetical order

� if three or more substituents, number to give them the lowest set of numbers and then list substituents in alphabetical order

Cycloalkanes

� Line-angle drawings

� each line represents a C-C bond

� each vertex and line ending represents a C

C

C CC

CC

C

C H2 C

H2 CCH2

CH

CH2

CH

CH3

CH3

C8 H1 6

Cycloalkanes

�� Example:Example: name these cycloalkanes

(a) (b)

(c) (d)

Bicycloalkanes

�� Bicycloalkane:Bicycloalkane: an alkane that contains two rings

that share two carbons

Bicyclo[4.4.0]decane(Decalin)

Bicyclo[4.3.0]nonane(Hydrindane)

Bicyclo[2.2.1]heptane(Norbornane)

(camphor)

monoterpenes

odorous

components

of plants

1,7,7-trimethylbicyclo

[2.2.1]heptan-2-one

Bicycloalkanes

� Nomenclature

� parent is the alkane of the same number of carbons as are in the rings

� number from a bridgehead, along longest bridge back to the bridgehead, then along the next longest bridge, etc.

� show the lengths of bridges in brackets, from longest to shortest

Bicyclo[2.2.1]heptane

1

2

3

4

5

67bridgehead

two C’s

one C

Isomers� relationships among isomers

Cis,Trans Isomerism

(Geometric isomers)

�� Cis,transCis,trans isomersisomers

� stereoisomers that are the result of the presence of

either a ring or a carbon-carbon double bond

Cis,Trans Isomers

� 1,2-Dimethylcyclopentane

CH3

trans-1,2-Dimethyl-cyclopentane

cis-1,2-Dimethyl-cyclopentane

H3 CH3 C CH3

CH3

H

CH3

H

H

HH

H

HH

H

H

CH3

H3 C

H

HH

HH

H

Cis,Trans Isomerism

� 1,4-Dimethylcyclohexane

t rans-1,4-Dimethyl-cyclohexane

cis-1,4-Dimethyl-cyclohexane

H

H3 C

CH3

H

H

H3 C

H

CH3

CH3

H3 C H3 C

CH3

Cis,Trans Isomerism� trans-1,4-Dimethylcyclohexane

� the diequatorial-methyl chair conformation

is more stable by approximately 2 x (7.28) =

14.56 kJ/mol

CH3

H

H

CH3

HH3 C

CH3

H(more stable)(less stable)

Cis,Trans Isomerism

� cis-1,4-Dimethylcyclohexane

conformations are of equal s tability

H

CH3

H

CH3

H

H3 C

H

CH3

Cis,Trans Isomerism� The decalins

H

H

H

H

B

H

H

A

B

H

H

A

trans-Decalin

cis-Decalin

Conformations

�� Conformation:Conformation: any three-dimensional

arrangement of atoms in a molecule that results

from rotation about a single bond

�� Newman projection:Newman projection: a way to view a molecule by

looking along a carbon-carbon single bond

Conformations

�� Staggered conformation:Staggered conformation: a conformation about a

carbon-carbon single bond in which the atoms or

groups on one carbon are as far apart as possible

from the atoms or groups on an adjacent carbon

H

H H

H H

H

Conformations

�� Eclipsed conformation:Eclipsed conformation: a conformation about a

carbon-carbon single bond in which the atoms or

groups of atoms on one carbon are as close as

possible to the atoms or groups of atoms on an

adjacent carbon

H

H H

H

HH

Conformations

�� Torsional strain Torsional strain

� also called eclipsed interaction straineclipsed interaction strain

� strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation

� the torsional strain between eclipsed and staggered ethane is approximately 12.6 kJ (3.0 kcal)/mol

+12.6 kJ/mol

Conformations

�� Dihedral angle (Q)Dihedral angle (Q): the angle created by two intersecting

planes

Conformations

� Ethane as a function of dihedral angle

Conformations

� conformations of butane as a function of

dihedral angle

Anti Butane

� Energy-minimized anti conformation

� the C-C-C bond angle is 111.9° and all

H-C-H bond angles are between 107.4

and 107.9°

Eclipsed Butane

Cyclopropane

�� angle strain:angle strain: the C-C-C bond angles are

compressed from 109.5° to 60°

�� torsional strain:torsional strain: there are 6 sets of

eclipsed hydrogen interactions

� strain energy is about 116 kJ (27.7

kcal)/mol

H

H

H

H

H

H

Cyclobutane

� puckering from planar cyclobutane

reduces torsional strain but increases

angle strain

� the conformation of minimum energy is

a puckered “butterfly” conformation


kcal)/mol

Cyclopentane

� puckering from planar cyclopentane

reduces torsional strain, but increases

angle stain

� the conformation of minimum energy is

a puckered “envelope” conformation


kcal)/mol

Cyclohexane

�� Chair conformation:Chair conformation: the most stable puckered

conformation of a cyclohexane ring

� all bond C-C-C bond angles are 110.9°

� all bonds on adjacent carbons are

staggered

Cyclohexane

� In a chair conformation, six H are equatorial and

six are axial

Cyclohexane

� For cyclohexane, there are two equivalent chair

conformations

� all C-H bonds equatorial in one chair

are axial in the alternative chair, and

vice versa

Cyclohexane

�� Boat conformation:Boat conformation: a puckered conformation of a

cyclohexane ring in which carbons 1 and 4 are bent

toward each other

� there are four sets of eclipsed C-H

interactions and one flagpole interaction

� a boat conformation is less stable than a

chair conformation by 27 kJ (6.5 kcal)/mol

Cyclohexane

�� TwistTwist--boat conformationboat conformation

� approximately 41.8 kJ (5.5 kcal)/mol

less stable than a chair conformation

� approximately 6.3 kJ (1.5 kcal)/mol

more stable than a boat conformation

Cyclohexane

� Equatorial and axial methyl conformations

Methylcyclohexane

CH3

CH3

+7.28 kJ/mol

alkana - website staff uistaff.ui.ac.id/system/files/users/tania.surya/material/alkana.pdf · the...

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