The presence of double bonds or rings within a molecule is indicated by a quantity called degree of
unsaturation.
When an alkane or a cycloalkane is treated with halogen (Cl2, Br2, F2, I2), a photochemical reaction
takes place, in which a C–H bond cleaves and a C–X bond is formed. In such reactions if one H-atom
is substituted by one halogen atom, then this is known as monohalogenation reaction.
Alkenes, Alkynes, polyenes or polyynes can be hydrogenated by using catalysts Ni/Pt/Pd at room temperature.
All Carbon–Carbon bonds(C=C, CC) get hydrogenate. The reaction can’t be stopped at any
intermediate stage
Ozonolysis reaction is used to determine the position of C=C, CC in a molecule. In this reaction Alkene,
Alkyne and polyalkene on ozonolysis undergo oxidative cleavage. It is of two types
When any compound release H2 gas after reaction with sodium or potassium or alkali metals or sodamide
then this reflect the presence of acidic hydrogen.
(i) Bromine water test ( Br2 + H2O, Red-brown solution) :
This is used to distinguish between saturated (alkane) and unsaturated (alkene/alkyne) hydrocabon
Cold dil. alkaline KMnO4 Pink/purple solution) :
This is also used to distinguish between saturated (alkane) and unsaturated (alkene/alkyne) hydrocabon
(i) Tollen’s Reagent [AgNO3 + NH4OH or {Ag(NH3)2}+ OH] :
Tollen’s Reagent gives white precipitate (Silver alkynide) with terminal alkyne.
(i) Lucas Reagent test (Conc. HCl + anhydrous ZnCl2)
* It gives white turbidity or cloudiness with alcohols (OH groups attached with sp3 carbon).
* Lucas Reagent used to distinguish between 1°, 2°, 3° alcohol because 1°, 2°, 3° alcohols react with different
rate.
Neutral FeCl3 test :
It form coloured complex with phenol or enol (OH groups attached with sp2 carbon
Carbonyl compouds (all aldehydes and ketones) give yellow–orange precipitate with 2,4–DNP. It is also
knwon as Brady’s reagent
(i) Tollen’s Reagent [AgNO3 + NH4OH or {Ag(NH3)2}+ OH] :
Tollen’s Reagent gives silver mirror or Black precipitate with aldehydes
Reagents : I2 + NaOH or NaOI Where R = H, alkyl, aryl group
Acetaldehyde, all methyl ketones, ethyl alcohol and all methyl alcohols give Iodoform test
(i) Sodium bicarbonate test (NaHCO3)
All the acids which are stronger than H2CO3 give CO2 gas with NaHCO3.
(i) NaNO2 + aqueous HCl test it is used to distinguish between 1º, 2º and 3º amines and also
distinguish between aliphatic and aromatic primary amines
1° Amine R–CH2–NH2 CHCl3 KOH R–CH2–N C + 3KCl + 3H2O
(unpleasent smell of isocyanide)
It is a test for 1º amine and aniline. Primary amine reacts with carbon disulphide to form dithioalkyl carbamic
acids which decompose on heating with mercuric chloride (HgCl2) to give alkyl isothiocyanates having
smell like mustard oil .
1° Amine R–NH2 + PhSO2Cl
Pyridine
R–NH–SO2–Ph
Base
Compund is soluble in base
Nitroalkane & nitrobenzene gives black ppt on reduction with Zn and ammonium chloride followed by
treating with Tollen’s reagent. This is also said to be Mulliken’s test.
Carbon and hydrogen are detected by heating the compound with copper(II) oxide. Carbon present in
the compound is oxidised to carbon dioxide (tested with lime-water, which develops turbidity) and
hydrogen to water (tested with anhydrous copper sulphate, which turns blue
Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by “Lassaigne’s
test”. The elements present in the compound are converted from their covalent form to their ionic form
by fusing the organic compound with sodium metal
The sodium fusion extract is boiled with iron(II) sulphate and then acidified with dilute sulphuric acid.
The formation of Prussian blue or green colour confirms the presence of nitrogen. Alternatively FeCl3
and dil. HCl may be added
(a) The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black
precipitate of lead sulphide indicates the presence of sulphur.
Na2S + (CH3COO)2Pb PbS
Black
The sodium fusion extract is acidified with nitric acid and then treated with silver nitrate. A white
precipitate, soluble in ammonium hydroxide shows the presence of chlorine, a yellowish precipitate,
sparingly soluble in ammonium hydroxide shows the presence of bromine and a yellow precipitate,
insoluble in ammonium hydroxide shows the presence of iodine
The compound is heated with an oxidising agent (sodium peroxide). The phosphorus present in the
compound is oxidised to phosphate
