Aliphatic Hydrocarbons

Aliphatic Hydrocarbons

1. 1
Aliphatic Hydrocarbons
Jully Tan
School of Engineering
EP101 / EG101 2
Learning Outcome
At the end of the lecture, students will be able to:
„Understand the family under organic compounds.
„Explain the aliphatic hydrocarbon or alkanes specifically by its structure, physical
and chemical properties.
„Naming the organic compound especially for alkanes according to IUPAC method.
„Explain the type of isomer in organic compound and draw the different isomer
structures of the compound.
„Explain the different type of the synthesis of alkanes and reaction of alkanes
specifically:
…Halogenation
…Combustion
…Hydrogenation of alkenes
…Reaction of Alkyl Halides with organometals
…Reduction of Alkyl Halides

2. 2
EP101 / EG101 3
Classes of Organic Compounds
Organic compound
Hydrocarbon
Alkane
Alkene
Alkyne
Hydrocarbon with O
Alcohol (-OH)
Ether/epoxide
Aldehyde/
Ketone
Carboxylic
acid
Carboxylic
Acid derivatives
Ester Halide acidsanydride
Halogeneted HC HC with N
Amine Amide
Nitrile
EP101 / EG101 4
Overview
¾Hydrocarbon
…Composed entirely of C and H atoms.
…Has 3 main categories
„Aliphatic - straight chain HC
„Cyclic - ring shape HC
„Aromatic – HC derived from benzene ring.
¾Each C can form a maximum of four single bonds, ORtwo single and one double bond, OR
one single and triple bond.

3. 3
EP101 / EG101 5
Some five-carbon skeletons
CC C C C
CC C C
C
CC C
C
C
C C C CC
CCC C C
CCC C
C
CC CC
C
C
CC
CC
C
C C
CC
CC
C
CC
C
C
C
CC
CC
C
CC
CC C C
C
single
bonds
double bond
ring
EP101 / EG101 6
Adding the H-atom skin to the C-atom skeleton
A C atom single-
bonded to two other
atoms gets two H
atoms.
CCC
H
A C atom single-
bonded to one other
atom gets three H
atoms.
CC
H
A C atom single-
bonded to three other
atoms gets one H
atom.
CCC
C
H
H
H H
A C atom single-
bonded to four other
atom is already fully
bonded (no H atoms).
CCC
C
C H
H
A double- and single-
bonded C atom or a
triple-bonded C atom
is treated as if it were
bonded to three other
atoms.
CC C
C C
H
H
A double-bonded C
atom is treated as if it
were bonded to two
other atoms.
CC

4. 4
EP101 / EG101 7
EP101 / EG101 8

5. 5
EP101 / EG101 9
Alkanes, C
n
H
2n+2
C
H
H
H
H
„carbon–carbon single bond: s (head–on) overlap of carbon sp
3
orbitals
„saturated hydrocarbons; only C-C and C-H bonds
„Alkane: a saturated hydrocarbon whose carbons are arranged in a chain. Saturated
hydrocarbon: a hydrocarbon containing only single bonds.
„Aliphatic hydrocarbon: another name for an alkane: aliphatic, “fat”
EP101 / EG101 10
1. Molecular Formula of Alkanes
10Decane
9Nonane
8Octane
7Heptane
6Hexane
5Pentane
4Butane
3Propane
2Ethane
1Methane
Molecular FormulaNo of CName

6. 6
EP101 / EG101 11
Structure
„Shape
…tetrahedral about carbon
…all bond angles are approximately 109.5°
EP101 / EG101 12
„Isomer: same chemical formula, but different structure.
„There are 2 isomeric butanes
…n-butane
…C
4H
10
…n means “normal” or in a straight chain
…isobutane
…C
4H
10
CCC
C
H
H
HH
H
H
H
H
HH
CCCCH
H
H
H
H
H
H
H
H
H
Branching vs. No Branching

7. 7
EP101 / EG101 13
Draw the structures for C
6H
14starting with the longest chain (6 in a row)
…next draw all structures with 5 carbons in the longest chain (substitute for the H s)
…then substitute for other H s
CCCCCCH
H
H
H
H
H
H
H
H
H
H
H
H
H
CCCCC
C
H
H
HH
H
H
H
H
H
H
H
H
HH
Find the Isomers of C
6
H
14
EP101 / EG101 17
Classification of C & H
„Primary (1°) C: a carbon bonded to one other carbon
…1° H: a hydrogen bonded to a 1° carbon
„Secondary (2°): a carbon bonded to two other carbons
…2°H: a hydrogen bonded to a 2° carbon
„Tertiary (3°) C: a carbon bonded to three other carbons
…3° H: a hydrogen bonded to a 3° carbon
„Quaternary (4°) C: a carbon bonded to four other carbons

8. 8
EP101 / EG101 18
C
C
PRIMARY
C
CC
C
CC
C C
CC
C
C
SECONDARY
TERTIARY QUATERNARY
CONNECTED TO ONE
OTHER CARBON
CONNECTED TO TWO
OTHER CARBONS
CONNECTED TO THREE
OTHER CARBONS
CONNECTED TO FOUR
OTHER CARBONS
Degree of Substitution
EP101 / EG101 19
2. Chemical Properties
„Not reactive compound:
…Alkanes are the least reactive among all other organic comp. They do not usually react
with strong acids or bases, or with most oxidizing or reducing agents.
„Highly combustible compound
…Alkanes can burn easily in combustion reactions and releasing high energy.
CH
4 O
2
CO
2
OH
2+ +

9. 9
EP101 / EG101 20
a. Both bp and mp increase with increasing carbon number for straight-
chain alkanes with formula C
n
H
2n+2
b. Branching tends to raise the melting pointand lower the boiling point. Why??
3. Physical Properties, Density & Solubility
„Alkanes physical forms as gas, liquid and solid.
…C
1
-C
4
-Gas
…C
5
-C
17
-Liquid
…C
18
and above -Solid
„Only dissolves in organic solvent, such as benzene, CCl
4
, but do not dissolve in
water (hydrophobic).
„Alkane is less density than water. (near 0.7 g/mL)
Why do alkane do
not dissolve in
water?
4. Boiling Point
Hint: surface area of alkane.
EP101 / EG101 21
b. Branching tends to lower the boiling pointand raise the melting point
BP 60
o
C 58
o
C 50
o
C
MP -154
o
C -135
o
C -98
o
C
Explanation:
MPBranching reduces the flexibility of the molecule which reduces the entropy term
∆S in the equation T
mp= ∆H/∆S. Since ∆S is in the denominator, T
mpincreases. The
structure of the alkane packed better into a compact 3D structure which is said the atom are
bonded more tightly and need higher T to transform the alkane from solid to liquid phase.
BP Branching reduces surface area (more compact structure), and therefore Van der Waals
dispersion forces which control boiling point for these molecules been reduces. Less energy
to overcome these reactions to transform liquid to gas phase.
Answer: Solubility – alkanes are nonpolar molecules and therefore insoluble in water, which
is polar. Alkanes are hydrophobic.

10. 10
EP101 / EG101 22
Boiling points of the first 10 unbranched
alkanes
EP101 / EG101 23
Boiling Points of Alkanes

11. 11
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EP101 / EG101 25
Sources
¾2 main sources are petroleum & natural gas

12. 12
EP101 / EG101 26
International
Union of
Pure and
Applied
Chemistry
“eye-you-pac”
colloquially:
Nomenclature
International Union of Pure and Applied Chemistry (IUPAC)
EP101 / EG101 27

13. 13
EP101 / EG101 28
1. Numerical Roots for Carbon Chains and Branches
Number of C atomsRoots/Parent
1
2
3
4
5
6
8
7
9
1
0
meth-
eth-
prop-
but-
hex-
pent-
hept-
oct-
non-
dec-
PREFIX + ROOT (Parent) + SUFFIX
EP101 / EG101 29
STEP 1 : Find the parent hydrocarbon
1. Find longest continuous chain of carbons and use as parent name.
2. If 2 chains have same number of carbons, choose the one with the more branch points.
STEP 2 : Number the atoms in parent chain
1. Begin at the end nearer to the first branch point.
Which one is the
correct way of
longest chain?
Which one is the
correct way of
numbering the
atom of the chain?

14. 14
EP101 / EG101 30
2. If branching occurs at equal distance from both ends, begin numbering at the end nearer the
second branch point.
Which one is the
correct way of
numbering the
atom of the chain?
EP101 / EG101 31
2. Naming the Compound Types of Suffix
„Suffix is the type of the family of that specifics organic compound.
„For example, alkanes, alkene and etc.
PREFIX
+ ROOT (Parent) + SUFFIX

15. 15
EP101 / EG101 32
3. Identify Prefix of the Chain
CH
3
CH
3
CH
3
-CH
2CH
2CH
2CH
2CH
3
-CH
2
CH
2
CHCH
3
-CH
2
CCH
3
neopentyl
isopentyl
pentyl
EP101 / EG101 33
STEP 1 : Identify and number the substituents
1.Give each substituent a number that corresponds to its position on the parent chain.
2.Two substituents on the same carbon gets the same number
Substituents
C3 CH2CH3 3-ethyl
C4 CH3 4-methyl
C6 CH2CH3 6-ethyl
Substituents:
C2 CH3 2-methyl
C4 CH3 4-methyl
C4 CH2CH3 4-ethyl

16. 16
EP101 / EG101 34
STEP 2: Write the name as a single word (follow alphabetical order)
1.Use hyphens to separate prefixes and commas to separate numbers or more identical
substituents are present, use multipliers (di, tri, tetra)
„Note : the multipliers are not use for alphabetizing.
Name a complex substituent as if it were a compound and put them in parentheses
EP101 / EG101 35
Naming & Drawing Cyclic Alkanes
Name of branching
group or substitute (if
any)
Parent
name
+
+
Use Prefix “cyclo”
Parent Name = longest continuous chain of carbon atoms
Cyclo = parent chain forms a ring
STEP 1: Find parent„If number of carbon atoms in the ring is larger than the number in the largest substituent, the
compound is an alkyl-substituted cycloalkane.
„If the number of carbon atoms in the ring is smaller than the number in the largest substituent,
the compound is an cycloalkyl-substituted alkane.

17. 17
EP101 / EG101 36
„STEP 2: Number the substituents and write the name
1.Start at a point of attachment and number the substituents so that the second substituent has
the lowest possible number.
2. If necessary, proceed to the next substituent until a point of difference is found.
3. If 2 or more substituents might potentially receive the same number, number them
alphabetical priority. Treat halogens as if they are alkyl groups.
Which one is the
correct way of
numbering the atom
of the chain?
Which one is the
correct way of
numbering the atom
of the chain?
EP101 / EG101 37
H
2C CH
2
CH
2
1. What is the parent name?
Propane (Longest chain is 3 carbons)
2. Is the parent chain in a ring?
Yes
Correct name is: cyclopropane

18. 18
EP101 / EG101 38
H
2CCH
CH
2
CH
3
Parent name is cyclopropane.
What is the branching group?Methyl –CH
3
Correct name is: methylcyclopropane
Note: The number (1) is not needed to identify the place of the substituent if
only one is present in the molecule.
EP101 / EG101 39
H
2CCH
H
2C
CH
3
CHCH
3
Parent name is cyclobutane.
What is the branching group?Methyl –CH
3
Correct name is: 1, 2-dimethylcyclobutane
Note: The first named substituent is arbitrarily given the number one (1) position
1
23
4

19. 19
EP101 / EG101 40
Reaction of Alkanes&
Synthesis of Alkanes
Reaction
„Halogenation
„Combustion
„Cracking & hydrocracking
Synthesis
„Hydrogenation of Alkenes
„Reduction of Alkyl Halides
„Reaction of Alkyl Halides with
organometals

20. 20
EP101 / EG101 42
Synthesis of Alkanes:
1. Hydrogenation of Alkenes
„Catalytic hydrogenation of alkene to form alkanes.
„General rxn eqn:
„Its take place under heterogenous ( more than 1 phase) system, the alkane & H2 are adsorbed on the
metallic surface. Therefore they are weakened (both multiple bond and H-H bond).
„The H2 will add to the same side of the multiple bond: cis-condition.
)()(
22/,2
AlkaneAlkene
HCHC
nnNiPdPtnn +
⎯⎯⎯→⎯
H
2
−−−⎯→⎯−+−=− CCHHCC
Pt
What is the
function of
the
catalyst??
EP101 / EG101 43
A: Hydrolysis by Grignard Reagent
ƒGridgnard reagent: prepared by treating an alkyl/aryl halide with magnesium mether in dry ether. General eqn. of
the preparing of Grignard reagent
ƒGrignard reagent is a reactive reagent. It can react with H2O to form Alkane.
IBrClX
grouparylalkylR
XMgRRMgXMgRX
reagent
Grignard
Ether
,,:
/:
+−
−⎯⎯→⎯+
δδ
Synthesis of Alkanes:
2. Reduction of Alkyl Halides
XOHMgHROHRMgX
reagent
Grignard
)(
2 +−⎯→⎯+

21. 21
EP101 / EG101 44
B: Reduction by metal & acid
ƒGeneral eqn.
ƒEg. Reduction of Cloro-cyclohexane with Zn & acetic acid able to produce 83% of cyclohexane.
ƒAlkyl halide as well react with Litium aluminium hydride (LiAlH
4
)
ƒTetrahydroaluminate ion will react with alkyl halide to produce alkane
RHRX
LiAlH
⎯⎯→⎯
4
RHRX
COOHCH
Zn
3
⎯→⎯
−−
+−−+−⎯→⎯−−+−− XHCHAlHXCHHAlH
tetrahydroaluminate Alkyl Halide Alkane
EP101 / EG101 45
ƒAlkane can be synthesis via nucleophilic substitution reaction between alkyl halide and a negative nucleophile.
ƒThe carbon in the polar carbon-halogen bond is positive, therefore the negative nucleophile is attracted to it.
LiXRCuRRXRCuLiR ++−⎯→⎯+
''
Cumprum diaalkyl Litium
2
3. Reaction of Alkyl Halides with organometals
RRuLiCRLiRRX
XRCuXLi
−+⎯⎯→⎯+⎯⎯→⎯−+⎯→⎯
'
2

22. 22
EP101 / EG101 46
Reaction of Alkane
1. Halogenation
EP101 / EG101 47
•Radical halogenation has three distinct parts.
Halogenation of Alkanes
•A mechanism such as radical halogenation that involves two or more
repeating steps is called a chain mechanism .
•The most important steps of radical halogenation are those that lead to
product formation—the propagation steps.

23. 23
EP101 / EG101 48
•When a single hydrogen atom on a carbon has been
replaced by a halogen atom, monohalogenation has
taken place.
•When excess halogen is used, it is possible to
replace more than one hydrogen atom on a single
carbon with halogen atoms.
•Monohalogenation can be achieved experimentally
by adding halogen X
2
to an excess of alkene.
•When asked to draw the produ cts of halogenation of
an alkane, draw the products of monohalogenation
only, unless specifically directed to do otherwise.
Halogenation of Alkanes
EP101 / EG101 49
•In the presence of heat or light, alkanes react with
halogens to form alkyl halides.
•Halogenation of alkanes is a radical substitution
reaction.
•Halogenation of alkanes is only useful with Cl
2or Br
2.
Reaction with F
2is too violent, and reaction with I
2is
too slow to be useful.
•With an alkane that has more than one type of
hydrogen atom, a mixture of alkyl halides may result.
Halogenation of Alkanes

24. 24
EP101 / EG101 50
EP101 / EG101 51
2. Combustion
C
n
H
2n+2
+ (xs) O
2
, flame Æn CO
2
+ (n+1) H
2
O + heat
gasoline, diesel, heating oil…
3. Pyrolyis (cracking)
alkane, 400-600
o
C Æsmaller alkanes + alkenes + H
2
Used to increase the yield of gasoline from petroleum. Higher
boiling fractions are “cracked” into lower boiling fractions that
are added to the raw gasoline. The alkenes can be separated and
used in to make plastics.

25. 25
EP101 / EG101 52
REVISION CHECKREVISION CHECK
What should you be able to do?
Recall and explainthe physical properties of alkanes
Recall and explainthe types of isomerism found in alkanes
Recall and explainwhy alkanes undergo chlorination free radical reaction
Writebalanced equations representing the reactions taking place in this
section
CAN YOU DO ALL OF THESE? CAN YOU DO ALL OF THESE? YES YES
NONO