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Reactions of Organic Chemistry
Revision for A Level Examination
Purpose

Reagent

Conditions

Observations/remarks

Alkenes (C=C)

Electrophilic Addition
[R]
Mild [O]

X2(l) in CCl4

room temp,
absence of UV

Reddish brown (or whatever
applicable) decolourises

C=C → RX
addition of hydrogen halide

HX(g)

room temp
(HX is polar, lower
temp)

reactivity: HI>HBr>HCl>HF
size of X ↓, length of H-X ↓,
overlap ↑, strength ↑

H2O(g),
conc
...
H2SO4

room temperature

#2: H2O(l)

Strong
[O]

C=C → RX
addition of halogen

heat

C=C → C–C
Used in production of
margarine (hardening oils to
produce solid fats)

H2

Ni catalyst with heat
OR
Pt/Pd catalyst, room
temp

Distinguishing test for C=C
and multiple bonds in alkene

Dilute KMnO4,
H2SO4 (aq)

C=C forms diol while C≡C
forms carboxylic acids

Dilute KMnO4,
NaOH (aq)

Formation of CO2,
carboxylic acid or ketone
helps to determine the
position of the C=C double
bond

Conc
...
KMnO4,
NaOH (aq)

[O]

Electrophilic Substitution

Arenes (B)
Nitration of benzene

Nitration of methyl benzene
Halogenation of benzene
and methylbenzene
X = Cl or Br
Preparation of
methylbenzene
Side chain oxidation

conc
...
H2SO4
(cat)
conc
...
H2SO4
(cat)
X2(g/l);
anhydrous
FeX3/AlX3 or Fe
(cat)
CH3Cl;
anhydrous FeCl3
or AlCl3
KMnO4(aq) (only
this can)

Heat under reflux at
55°C

Yellow oil (nitrobenzene, b
...

210°C) formed

30°C

Mixture of 2-nitro and 4-nitro

Room temperature
(for latter: absence
of UV light)

Steamy white fumes of HX(g)
evolved, yellowish green
Cl2/reddish-brown Br2
decolorises

Room temperature

Heat

White ppt of benzoic acid
formed, purple KMnO4
decolourised

1

Reactions of Organic Chemistry
Revision for A Level Examination
Purpose

Reagent

Conditions

Observations/remarks

Elimination

Nucleophilic Substitution

Halogen Derivative (RX)
RX → R–OH

NaOH or KOH
(aq)

Heat under reflux

**Aqueous is needed for NuS
...

Sodium phenoxide forms i-d

conc
...

H2SO4

170°C

Al2O3

heat to 350°C

2°ROH → RCOR

Elimination

3°ROH → no rxn

ROH → C=C

steamy white fumes
...
NaOH will hydrolyse
aliphatic
...

H2SO4

Heat under reflux

reagents form HBr

I2 and red P

Heat under reflux

NaI and conc
...
HNO3

room temp

Bromination of phenols

Br2(aq)
(halogen carrier
not required)

room temp

monobromination of phenols

Br2

in CCl4

Distinguishing phenols

Electrophilic Substitution

(2P + 3Br2) or
PBr3

Neutral FeCl3(aq)

room temp

ROH → RBr

ROH → RI
Nitration to form 2- and 4nitrophenols
Nitration to form 2,4,6trinitophenol

reagents form PI3 as it is not
stable to be stored
reagents form HI; H2SO4 can
[O] HI to I2
Ring is activated by OH
(EDG), thus no need cat
stronger reagent to allow
multiple substitutions
reddish-brown of Br2
decolourises and white 2,4,6tribromophenol ppt
Steamy white fumes
2- and 4-bromophenol
obtained
Purple colouration

Carbonyl Compounds – Aldehydes (RCHO) Ketones (RCOR)

[R]

RCHO → 1°ROH
RCOR → 2°ROH

heat
in dry ether
heat
Orange K2Cr2O7 turns green or
purple KMnO4 decolourises
Heat under reflux
colour remains

RCHO/ RCOR →
RC(OH)CN
Extend carbon length and
add an –OH group

HCN(g) in the
presence of a
trance amount of
NaOH or NaCN

test for aldehydes or
ketones

2,4-DNPH

warm

orange ppt

test for aliphatic aldehydes
benzaldehyde

Fehling’s reagent
(a mixture of
2+
Cu /NaOH(aq))

warm

reddish brown ppt of Cu2O

test for aldehydes

Tollen’s reagent

warm

shiny silver mirror

[O] in
OH

Nucleophilic
Addition

RCOR → no rxn

in dry ether

Con
den

[O]

RCHO → RCOOH

LiAlH4
NaBH4
H2(g), Ni (cat)
LiAlH4
NaBH4
H2(g), Ni (cat)
K2Cr2O7 , H2SO4
(aq)
or
KMnO4 , H2SO4
(aq)

alcohol as solvent
10°C - 20°C

for the RX rxn, it is only to
extend carbon length
...
KMnO4,
H2SO4(aq)

heat

C6H5CH3 → BCOOH

KMnO4(aq),
H2SO4(aq)

heat

methyl ROH/RCOR →
RCOOH

Hydroly
sis

H2SO4(aq) or
HCl(aq)
NaOH(aq) then
acid

C=C → RCOOH
oxidative cleavage

I2(aq), NaOH(aq)
then
H2SO4/HCl(aq)
Na2CO3
(or any other
carbonate)

heat
heat then room
temp

Neu

RCO2H → RCO2

[R]

RCOOH → 1° ROH

LiAlH4

in dry ether

[O]

HCOOH/C2H2O4 → CO2 +
H2O

KMnO4(aq),
H2SO4(aq)

heat under reflux

Nu Acyl
Sub

RCOOH → RCOCl

PCl3 or PCl5 or
SOCl2

room temp

steamy white fumes of HCl;
reaction similar to that of ROH
→ RX

Hydr
ol

warm

Generally avoid HNO3 as NO3
cause redox
need to acidify to get the
RCOOH
purple KMnO4 decolourises
can be used to shorten carbon
chain
purple KMnO4 decolourises,
white ppt of benzoic acid
(K2Cr2O7 too mild to form
benzoic acid)
Idoform test is in alkali
medium
...

Confirm presence of RCOOH
from R(B)OH
NaBH4 and catalytic
hydrogenation cannot be used
as they are not strong enough
RA
Generally RCOOH cannot be
[O]
HCOOH is the only acid that
can be oxidized by Tollen’s or
Fehling’s
To get methanoic and
ethanedioic acid, milder OA
should be used on their ROH

RCOCl → RCOOH

H2O

room temp

solution of HCl(aq) is formed

Conde
nsation

[O]

RCN → RCOOH
(acidic hydrolysis)
RCN → RCOOH
(alkaline hydrolysis)

RCOCl → RCON(H)
(form amides)

NH3, R-NH2, R2NH
(3° don’t have
cause no H)

room temp

RCOOH undergo
neutralisation with NH3 and
amines instead of
condensation

-

room temp

Nitrogen Compounds – Amines (RNH2) Amide (RCONH2)
H2(g), Ni (cat)
H2(g), Pd/Pt (cat)
[R]

RCN → 1° RNH2

heat
room temp

LiAlH4 in dry
ether

room temp

Na in ethanol
(B)NO2 → (B)NH2
Reduction of nitrobenzene

Sn, conc
...

Phenol also give similar
observation, because –OH and
–NH2 are highly ring activating

Conditions

Observations/remarks
RCOOH undergo
neutralisation with NH3 and
amines instead of
condensation

room temp

*repeated from RCOOH

Br2(aq)
(halogen carrier
not required)

room temp

reddish-brown of Br2
decolourises and white 2,4,6tribromophenylamine ppt
Steamy white fumes
*repeated from phenol

heat

Reversible and incomplete

RCN → RCOOH
(alkaline hydrolysis)

NaOH(aq)

heat then room
temp

OH stronger Nu, faster and to
completion

HCl(aq) or
NaOH(aq)

room temp

Simple acid-base reaction

Neu

H2SO4(aq) or
HCl(aq)

amino acid can act as a
base or acid

Condens
ation

RCN → RCOOH
(acidic hydrolysis)

forming amide

Hydrolysis

Hydrol

Elec Sub

Condens
ation

Purpose

Complete hydrolysis of
proteins
Gives number and relative
amts of AA; does not give
sequence

Takes place readily in living organisms
where suitable enzymes are catalysts
H2SO4(aq) or
HCl(aq)

heat under reflux for
several hours

NaOH(aq)

-

a peptide linkage is a type of
amide bond found in natural
polymer – proteins
several hours needed cause
there are a lot of peptide
linkages; bear in mind the
medium and decide where to
protonate or deprotonate

Uses of some chemicals
ethanolic silver nitrate

AgNO3

ethanolic silver ethanoate

AgCH3COO

Sodium Metal

Na

test for –OH groups

Potassium dichromate(VI)

K2Cr2O7

distinguish 1°/2° and 3° ROH

phosphorus pentachloride

PCl5

thionyl chloride

SOCl2

test for –OH groups in ROH and RCOOH
only

NaOH(aq), I2(aq); warm

Idoform

test for certain methyl alcohol and
carbonyl

aqueous bromine

Br2(aq)

test for phenol or phenylamine

neutral Iron(III) Chloride

FeCl3(aq)

test for phenol

2,4-dinitrophenylhydrazine

2,4-DNPH

test for aldehydes or ketones

Fehling’s reagent

Cu /NaOH

Tollen’s reagent

Ag /OH

sodium carbonate

Na2CO3

2+

+

-

identify halide ions from halogen
derivatives

test for aliphatic aldehydes
test for aldehyde
test for RCOOH

5



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