LECTURE NOTE SK025 (ORGANIC) KMKt

Examples of electrophiles : Examples of nucleophiles :

 cations such as H+, H3O+, y
NO2+, Br+ etc.
❖ anions such as OH-, RO-,
 carbocations (species Cl-, CN- and etc.
with a positive )c.hea.grgCeHo3n+
carbon atoms ❖ carbanions (species with a
negative charge on carbon
 Lewis acids such as AlCl3, atoms ). e.g CH3-
FeCl3, BF3 and etc.
❖ Lewis bases which can
 Site of low electron donate lone pair electrons such
density as NH3, H2O, H2S etc.

d+ d- d+ d- ❖ Site of high electron density
C=O C–X (carbon-carbon multiple
bonds):
Carbonyl haloalkane C = C (alkenes, arenes);
C  C (alkynes)
 oxidizing agents such as
Cl2, Br2 etc.

Example 5

Label the electrophilic and
nucleophilic sites in each molecule:

a) b) H2O c)

Br

d)
N
CH3

Answer nucleophilic

nucleophilic b) d–
a) d+ O d+
H
d+ Brd– H
electrophilic
electrophilic
nucleophilic
c) d) nucleophilic

d– d+
N
CH3

electrophilic

Addition Elimination

GENERAL TYPES OF
ORGANIC REACTIONS

Substitution Rearrangement

ADDITION REACTION

All parts of the adding reagent appear in the
product
Two molecules become one

Characteristic reaction of compounds with
multiple bonds

Example:

HH H Br
H CCH
CC + H Br
HH
HH

ethylene bromoethane
(an alkene) (an alkyl halide)

ELECTROPHILIC ADDITION

Reactions involving C═C and C≡C
p bonds are electron–rich and located above
and below the plane of the bond
 susceptible to attack by electrophiles

Come attack me,
Mr. electrophile!
You love electrons, right?
I’m electron–rich!

alkene

Example:

HH + Br Br HH
H CCH
CC
Br Br
HH
HH
H H + H Cl H CCH
C C
H Cl
H H
HH
H H + H OH H CCH
C C
H OH
H H

NUCLEOPHILIC ADDITION

Most common reaction of aldehydes and
ketones

Nucleophile approach to the electrophilic
C of carbonyl group

d+ O d– ●●Nu

C

Example: ●●O●●●●– H+ OH
R C CN R C CN
●●O●●
R C R’ + CN– R’ R’
ketone/aldehyde cyanohydrin

SUBSTITUTION REACTION

Two reactants exchange parts to give new
products

Characteristic reaction of saturated and
aromatic compounds

Example:

H light H H Cl
H C Cl +
H C H + Cl Cl
H
H chloromethane
methane (an alkyl halide)
(an alkane)

ELECTROPHILIC AROMATIC
SUBSTITUTION

The characteristic of all aromatic compounds
Benzene has six p electrons delocalized in
six p orbitals that overlap above and below
plane of the ring (electron–rich)
 susceptible to attack by electrophiles

benzene

Example:

FeBr3 Br
+ Br Br + H Br

benzene bromobenzene

NUCLEOPHILIC SUBSTITUTION

Most common reaction of alkyl halides
(haloalkanes)

d+ d–

Nu:– + R–X → R–Nu + X–

Example:

HO– + CH3–I → CH3–OH + I–
I– + CH2CH3–Cl → CH3CH2–I + Cl–

SUMMARY OF TYPES OF
ORGANIC REACTIONS

Electrophilic addition  alkenes, alkynes

Electrophilic aromatic  aromatic
substitution compounds

Nucleophilic addition  aldehydes,
ketones

Nucleophilic substitution  alkyl halides

Free radical substitution  alkanes

11.4-12

ELIMINATION REACTION

Opposite of addition reaction

A single reactant splits into two products

Method for preparing compounds with double
and triple bonds

Example: base HH + H Br
CC
H Br
H CCH HH

HH

bromoethane ethylene small
(an alkyl halide) (an alkene) molecule
eliminated

REARRANGEMENT REACTION

A single reactant undergoes a reorganization of
bonds and atoms

Example:

CH3CH2 H H3C H
C C
CC acid catalyst
H CH3
HH

1–butene 2–butene

Example 6

Classify each of the following
reactions as an addition, elimination,
substitution, or rearrangement:

a) CH3Br + KOH → CH3OH + KBr
b) CH3CH2OH → H2C═CH2 + H2O
c) H2C═CH2 + H2 → CH3CH3
d) CH2═CHOH → CH3CHO

Answer

a) CH3Br + KOH → CH3OH + KBr
 nucleophilic substitution

b) CH3CH2OH → H2C═CH2 + H2O
 elimination

c) H2C═CH2 + H2 → CH3CH3
 Electrophilic addition

d) CH2═CHOH → CH3CHO
 rearrangement

Edited By: Revised By:
AAL,SAMN,NM JA

Approved By:
ZA

END OF
SLIDE SHOW

CHAPTER 5
HYDROCARBONS

5.1 Alkanes
5.2 Alkenes

1

TYPES OF
REACTION

5.1 ALKANES

2

Learning Outcomes

a) Classify hydrocarbons into:
i) aliphatic and aromatic
ii) saturated and unsaturated

b) Give the name of alkanes according to the
IUPAC nomenclature

c) Give the structure formulae of the following alkanes:
i) straight chain and branched alkanes
(parent chain ≤ C10)
ii) cyclic alkanes (C3-C6)
iii) alkyl groups

HYDROCARBON

compounds which
contain only carbon and

hydrogen atoms.

HYDROCARBONS ALIPHATIC saturated contain C-C
alkanes
AROMATIC e.g :

contain one or more unsaturated contain
benzene ring C=C

e.g: alkenes

e.g :

e.g : contain C≡C

e.g :
alkynes 5

DRAW & NAME IUPAC
NOMENCLATURE OF ALKANES

straight chain & alkyl groups

branch alkanes
(parent chain ≤

C10)

cyclic alkanes
(C3-C6)

66

ALKANES

• IUPAC names have the –ane suffix.

• General formula for straight chain of alkanes is
CnH2n+2 where n ≥ 1

• General formula for cycloalkanes is CnH2n
where n ≥ 3

• Starting from C4H10 onwards, the alkanes show
the phenomenon of chain isomerism.

• They can exist as linear or branched alkanes.

7

Example : C5H12
Linear alkane:

Branched alkanes:

8

Nomenclature of Alkanes

Alkane Molecular Structural formula No. of
formula carbon
Methane CH4
Ethane CH4 CH3CH3 1
Propane C2H6 CH3CH2CH3 2
Butane C3H8 CH3CH2CH2CH3 3
Pentane C4H10 CH3(CH2)3CH3 4
Hexane C5H12 CH3(CH2)4CH3 5
Heptane C6H14 CH3(CH2)5CH3 6
Octane C7H16 CH3(CH2)6CH3 7
Nonane C8H18 CH3(CH2)7CH3 8
Decane C9H20 CH3(CH2)8CH3 9
C10H22 10

9

IUPAC NOMENCLATURE

Rules in Naming
Branched Alkanes

⮚ Naming branched alkanes is slightly more
complicated than naming the straight chain ones.

⮚ So you need to follow a simple set of steps to
arrive at a proper name.

10

STEP 1: Choose the longest continuous
chain of carbon atoms; this chain
determines the parent name for
alkanes.

Example:

CH3CH2CH2CH2CHCH3 CH3CH2CH2CH2CHCH3
CH3 CH2
CH3
Parent name: hexane
Parent name: heptane

11

STEP 2: Number the longest chain

beginning with the end of the
chain nearer the substituent.

Example:

6 5 4 3 21 76 54 3
CH3CH2CH2CH2CHCH3
CH3CH2CH2CH2CHCH3

substituent CH3 2 CH2

1 CH3

substituent

12

STEP 3: 1. Use rule no. 1 to locate the

position of the substituent.

Example: 2. The position and the name of the

substituent must be written in

front of the parent chain.
Substituent
methyl at C-3

6 5 4 3 21 76 54 3

CH3CH2CH2CH2CHCH3 CH3CH2CH2CH2CHCH3
2 CH2
Substituent CH3 1 CH3
methyl at C-2

2-methylhexane 3-methylheptane
13

Some Common Substituent Groups

Alkane Name Substituent

methane methyl CH3
ethane ethyl CH2CH3
propane propyl CH2CH2CH3

isopropyl CHCH3
CH3
butane butyl
CH2CH2CH2CH3

14

isobutyl CH2CHCH3
sec-butyl
tert-butyl CH3
neopentyl CHCH2CH3

CH3 15
CH3
CCH3
CH3

CH3
CH2CCH3

CH3

cyclopropyl −C6H5 or
cyclobutyl
CH2
phenyl
benzyl

16

Name Substituent
bromo -Br
chloro -Cl
fluoro -F
-I
iodo -OH
hydroxyl -NH2
-CN
amino -NO2
cyano
nitro

17

STEP 4: If the compound contains more than one

identical substituents, use prefixes:
▪di- : (2 identical substituents)
▪tri- : (3 identical substituents)
▪tetra- : (4 identical substituents)

☞ Commas are used to separate numbers
from each other.

Example : CH3

1 234 1 2 34 5

CH3CH CHCH3 CH3CH CHCHCH3
Cl Cl
CH3 CH3
2,3-dichlorobutane
2,3,4-trimethylpentane

18

STEP 5: If two substituents are present on

the same carbon atom, use that
number twice.

Example :

CH3

34 56
C CH2 CH2CH3
H3C

2 CH2

1 CH3

3,3-dimethylhexane

19

STEP 6: If two or more substituents are

present, give each substituent a
number corresponding to its
location on the longest chain.

❑ the substituent should be listed
alphabetically.

❑ In alphabetizing, the prefixes di,
tri, tetra, sec-, tert- are ignored
except iso and neo.

20

Example 1:

CH3

7 6 54 32 1

CH3CH2CH CH2 CCH2CH3

CH3CH2 CH3

5-ethyl-3,3-dimethylheptane

21

Example 2 :

CH3

87 6 54 32 1
CH3CH2CH2CH CH2 CCH2CH3

H3CCHCH3 CH3

5-isopropyl-3,3-dimethyloctane

22

STEP 7: If there are two chains of equal
length as the parent chain, choose
the chain with the greater number of
substituents.

7 6 5 4 3 21

Example :

5

6

7

2,3,5-trimethyl-4-propylheptane
(4 substituents)

4-sec-butyl-2,3-dimethylheptane 23
(3 substituents)

STEP 8: If branching occurs at an equal
distance from either end of the
Example : longest chain, choose the name
that gives the lower number at the
first point of difference.

6 5 4 32 1

1 2 3 4 25 6

2,3,5-trimethylhexane
2,4,5-trimethylhexane

24

Rules in Naming
Cyclic Compounds

25

• Cycloalkanes: alkanes which carbon atoms
are joined in rings.

• Cycloalkanes are known as saturated
hydrocarbon, because it has the maximum
number of bonded hydrogen (only has
single bonds).

• General formula:
CnH2n where n = 3, 4, 5, ……

26

STEP 1: Prefix cyclo- is used to name cyclic

compound with a single ring system.

Example :

C3H6 cyclopropane

C4H8 cyclobutane

C5H10 cyclopentane

C6H12 cyclohexane

27

STEP 2: If only one substituent is present, it

is not necessary to designate its

position.

Example : Cl

chlorocyclopropane

CH3 methylcyclohexane

28

STEP 3:

⮚ If two substituents are present, number
carbon in the ring beginning with the
substituent according to the alphabetical
order.

⮚ Number in the direction that gives the next
substituent the lowest number possible.

29

Example 1:

3 CH
4
3
5
2

1 CH2CH

63

1-ethyl-2-methylcyclohexane
NOT

1-ethyl-6-methylcyclohexane

30