alkane-full notes fazli

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DR. JOAZAIZULFAZLI JAMALIS

Department of ChemistryFaculty of Science

Universiti Teknologi Malaysiajoazaizul@kimia.fs.utm.my

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Hydrocarbons

Aliphatic Aromatic (Arenes)

• Alkane • Alkene • Alkyne

Benzene&

derivatives

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Alkanes all bonds are single bonds (C-C and C-H, bonds) Known as saturated

hydrocarbons Categorized as acyclic or cyclic General formula for acyclic

alkanes: CnH2n+2

General formula for cyclic alkanes:

CnH2n

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Acyclic alkanes contain only linear and branched chains of carbons atoms.

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Cyclic alkanes are also known as cycloalkanes.

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Alkanes Homolog Number of Carbon Atoms Methane 1Ethane 2Propane 3Butane 4Pentane 5Hexane 6 Heptane 7Octane 8Nonane 9Decane 10

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Cycloalkanes Homolog

Number of Carbon Atoms Cyclopropane 3Cyclobutane 4Cyclopentane 5Cyclohexane 6Cycloheptane 7

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Types of Carbons and HydrogensC - primary (1), secondary (2), tertiary (3) & quaternary (4)

H - primary (1), secondary (2) & tertiary (3)

CH

HHCHCH

HCH

HH

C HH

H

3o

3o 2o

2o

2o

1o

1o

1o1o1o

1o

1o

1o

1o

1o

TRY THIS !!!

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C

C

C

CC C

HH

HH

HH

H

H

H

HH

HH

H

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Alkyl Groups- removing one hydrogen atom from the alkane

- substituent groups

- The symbol is R.Alkane Alkyl group AbbreviationCH3-H

methaneCH3-

methylMe-

CH3CH2-Hethane

CH3CH2-ethyl

Et-

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Propyl (remove 1 H from propane)

CH3CHCH3

Isopropyl (remove 2 H from propane)

CH3CH2CH2

CH3CH2CH3propane

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n- Butyl (remove 1 H from butane) CH3CH2CH2CH2

sec-Butyl (remove 2 H from butane) CH3CH2CHCH3

CH3CH2CH2CH3n-butane

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isobutyl (remove 1 H from isobutane) C

CH3H3C

HCH2

tert-butyl or t-butyl (remove 3 H from isobutane) C

CH3H3C CH3

CH3CHCH3CH3

isobutane

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IUPAC NAMESInternational Union of Pure and Applied

Chemistry

Rule 1: Determine the main chain1. Find the longest continuous chain of carbon atoms, and name it.2. Use the chain with greater number of substituents as the main chain.3. Substituents can be an alkyl groups, hydroxyl groups (-OH), halogen (-Cl,-Br,-I,-F), phenyl groups etc.

CH3CH2CH2CH2CHCH2CH2CH3CH3

12345678

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CH3CHCH2

CH- CHCH2CH3

CH3

CH3CH- CH3CH3

4. Determine the chain with the greater number of substituents

CH3CH2CH2CH2CHCH2CH3CH2CH2CH3

123

45678

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Rule 2 & 3: Numbering the Main Chain and naming the

alkyl groups

1. Number the longest chain, start with the end of the

chain nearest to a substituent2. Substituted carbons always get the lowest

possible number

CH3CHCH2CH2CH3CH3

1 2 3 4 5

2-methylpentane (IUPAC)isohexane (common name)

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CH3CH2CHCHCHCH2CH3

CH3

CH3

CHCH3

CH31

2

34567

3-ethyl-2,4,5-trimethylheptane

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when two or more substituents are present, list them in alphabetical order. when two or more of the same alkyl groups (or other substituent) are present, use the prefixes di-, tri-, tetra-, hexa- etc. follow the alphabet of the alkyl groups, NOT the prefixes di-, tri-, tetra- (IGNORE alphabet of the prefixes)

Rule 4: Organizing multiple groups

CH3CHCHCH2CHCH2CH3

CH2CH31 2 3

4 5 6 7

CH3

CH3

5-ethyl-2,3-dimethylheptane

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CH3CH2CCH2CH2CHCHCH2CH2CH3

CH2CH31 2 4 5 6 7

CH2CH3 CH2CH3

CH33

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9 10

3,3,6-triethyl-7-methyldecane

CH3CH2CHCH2CHCH2CH2CH3CH3 CH2CH3

1 2 3 4 5 6 7 8

5-ethyl-3-methyloctane

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When both directions lead to the same lowest number for one of the substituents, choose the direction that gives the lowest possible number to the remaining substituents.

CH3CCH2CHCH3CH3

CH3

CH3

2 4

2,2,4-trimethylpentaneNOT

2,4,4-trimethylpentane

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CH3CH2CHCHCH2CHCH2CH3CH3

CH3 CH2CH31 3 4 6

6-ethyl-3,4-dimethyloctane [6,3,4] NOT3-ethyl-5,6-dimethyloctane [3,5,6]

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If the same number is obtained in both directions, follow the alphabet of the substituent.

CH3CH2CHCHCHCH2CH3

CH3 CH2CH3

CH3134

5

3-ethyl-4,5-dimethylheptane

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CH3CHCHCH3

Cl

Br

2-bromo-3-chlorobutaneNOT

3-bromo-2-chlorobutane

CH3CH2CHCH2CHCH2CH3

CH2CH3

CH3

3-ethyl-5-methylheptaneNOT

5-ethyl-3-methylheptane

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Certain common names are still used in the IUPAC system Eg.

CH3CHCH2

CH3CH3CH

CH3

Isopropyl Isobutyl

CH3CH2CH2CH2CHCH2CH2CH3CHCH3CH3

4

1 2

4-isopropyloctane or 4-(1-methylethyl)octane

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CH3CH2CH2CH2CHCH2CH2CH2CH2CH3CH2CHCH3

CH3

5

1 2 3

5-isobutyldecaneor

5-(2-methylpropyl)decane

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Cycloalkanes Rings of carbon atoms (CH2 groups) Formula: CnH2n

Nonpolar, insoluble in water Compact shape Melting and boiling points similar to branched alkanes with same number of carbons

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Nomenclature of Cycloalkane

H3C Cl

methylcycloheptane chlorocyclohexane

no number is needed for a single substituent on a ring

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CH3

CH2CH2CH2CH2CH3

methylcyclopentane

1-cyclobutylpentane

May be cycloalkyl attachment to chain.

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if more than one substituent, arrange in alphabetical order

give number to the carbon of the ring choose the “best” combination of numbers

CH2CH3H3C

CH3CH2CH2 1

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12

3

4

4

4-ethyl-2-methyl-1-propylcyclohexaneNOT

1-ethyl-3-methyl-4-propylcyclohexaneNOT

5-ethyl-1-methyl-2-propylcyclohexane[4,2,1]=7[1,3,4]=8[5,1,2]=8

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H3C CH3CH3

1,1,3-trimethylcyclopentaneNOT

1,3,3-trimethylcyclopentaneNOT

1,1,4-trimethylcyclopentane

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Complex Substituents If the branch has a branch, number the

carbons from the point of attachment. Name the branch off the branch using a

locator number. Parentheses are used around the complex

branch name.

1 23

1-methyl-3-(1,2-dimethylpropyl)cyclohexane

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Isomerism

Molecules which have the same molecular formula, but differ in the arrangement of their atoms, are called isomers.

Constitutional (or structural) isomers differ in their bonding sequence.

Stereoisomers differ only in the arrangement of the atoms in space (in alkene).

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Structural Isomers

CH3CH2OHO CH3H3C and

C4H1

0

CH3CH2CH2CH3 and CH3CHCH3

CH3

C2H6O

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Geometric Isomerism in CycloalkanesThe lack of free rotation of single-bonded

carbons in a ring produces a kind of isomerism called geometric isomerism.

CH3CH3

HH

cis 1,2-dimethylcyclopropane

HCH3

CH3H

trans 1,2-dimethylcyclopropane

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1. Natural gas methane (60%-80%) ethane, propane and butane

2. Petroleum gasoline C5H12-C12H26 kerosene C12H26-C16H34 diesel fuel C15H32-C18H38

Source of alkanes

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Physical Properties of Alkanes1. Alkanes from C1 to C4 are gasses

C5 to C17 are liquids >C18 are wax-like solids

2. Alkanes are nonpolar compounds. Their characteristic known as “like

dissolves like” rule. Nonpolar compounds are soluble in

other nonpolar solvents. Alkanes are soluble in organic

solvents.

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3. Boiling Points (bp)a. Alkanes have low bp’s compared to

more polar compounds of comparable size

CH3CH2CH3 CH3CH2OHCH3CHO

MW= 44BP= -42oC

Van der Wall forces (weak)

MW =44BP=21oC

dipole-dipoleattraction

MW = 46BP=79oC

hydrogen bonding (strong)

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b. Boiling points(b.p) increases as the numbers of carbons increases because of increased surface area

CH3CH2CH2CH3 b.p = 0oC

CH3CH2CH2CH2CH3 b.p = 36oC

CH3CH2CH2CH2CH2CH3 b.p = 69oC

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c. The b.p of isomers decrease with branching

because of decreased surface areabranched alkanes are more compact, less surface contact between molecules, less van der Waals attractions.

CH3CH2CH2CH2CH3CH3CH2CHCH3

CH3b.p = 36C b.p = 28C

CH3CCH3CH3

CH3

b.p =10C

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Synthesis of Alkanes1. Hydrogenation of Alkenes

Alkene + H2 Alkane Catalyst required, usually Pt, Pd,

or Ni.

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2. Reduction of alkyl halide Sources of H: Zn / CH3COOH, LiAlH4,

NaBH4

CH3CH2CH2CH2Br CH3CH2CH2CH3LiAlH4

HCl Zn

CH3COOH

HH

ZnCH3COOHR X R H

orLiAlH4

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3. Reduction of alkyl halide via Grignard Reagent add an organometallic reagent to water this will reduce an alkyl halide to an alkane

R + HMgX O H R H Mg(OH)X+

Grignard Reagent react with water molecule:

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Reactions of Alkanes1. Combustion

2. Cracking and hydrocracking (industrial)

3. Halogenation

2 CH3CH2CH2CH3 + 13 O2heat

8 CO2 + 10 H2O

CH4 + Cl2heat or

light CH3Cl + CH2Cl2 + CHCl3 +CCl4

long chain alkane shorter chain alkanecatalyst

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Mechanism of HalogenationStep 1 (Initial Step)Homolytic cleavage of the chlorine molecule

Cl Cl hvor heat

2 Cl

Step 2 (Propagation Step)i) Chlorin radical attack alkane molecule to form alkyl radical

ii) Alkyl radical will attack chlorine molecule to produce chlorine radical

R + + ClCl Cl R Cl

ClR H + HCl + R

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Step 3 (Termination Step)Free radicals will combine or transfer its electrons to form a molecule

R + R R R

Cl + Cl Cl Cl

R + Cl R Cl

Halogenation will give mixtures of products because

there are more than one atom of hydrogen that will be substituted.

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Try This !!!

Propose the mechanism for the following reaction. Which compound is the major product. Explain your answer.

CH3CH2CH3 + Cl2heat oruv light

?