Introducation to organo metallic compund or grignard reagent, structure, prepration, physical and chemical properties, types of chemical reaction, applications, by AMIR HASSAN FROM GPGC MARDAN, KPK, PAKISTAN.

1. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM
INTRODUCATION TO ORGANO-MEGNESIUM
OR GRIGNARD REAGENT
DISCOVERY:-
A scientist victor Grignard discovered the organic compound in which the carbon
is directly attached with magnesium (a metal) and a halogen atom (indirectly), commonly known
as organo-magnesium but they were later on name as a Grignard reagent after his discoverer.
A Victor Grignard got noble prize in 1912 on it, because a lot organic compound can be
synthesis on it such as alkanes, alkenes, alkynes, alcohol, aldehyde, ketones, and carboxylic acid.
DEFINITION:-
An organo-metallic compound in which the carbon is directly attached
magnesium and indirectly attached with halid commonly called organo-magnesium halid or,
Grignard reagent.
GENRAL FORMULA FOR GRIGNARD REAGENT :-
The general formula for Grignard reagent can be written as follows
 Where R: is alkyl, alkenyl, alkynyl, or aryl group. i.e. may be single bonded, double
bonded, triple bonded, aromatic, alicyclic, hetrocyclic, bridgehead etc.
 Where X: is Cl2, Br2, I2, (F2 not included due to high electronegativity of flourine and
explosive nature the nucleophilic and basic character of R group would not exsist).
 Example are the following

2. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM
STRUCTURE OF GRIGNARD REAGENT :-
The orbital of organo-metallic compound provide us useful information about the relative reactivities
of these compounds. The reactivity of compound determined by strength of carbon – metal bond.
The stronger the bond less reactive the compound will be.
 The carbon – metal bond in methyl –magnesium chloride result as overlap of sp orbital of
Magnesium and sp3
orbitalof methyl group.
 A magnesium atom has electronic structure :
Mg12 : 1s2
, 2s2
,2p6
, 3(sp)1
, 3(sp)1
 The sp orbital of magnesium are oriented at 1800
and available for the formation of bond with
sp3
orbital of alkyl group or, a valency orbital of halogen atom.
 Here sp orbitalof magnesium is less diffused so, degree of overlap to form carbon –
magnesium bond will be comparatively more effective and more stronger (and less polar).
 The structure are as follows :

3. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM
PREPRATIONOF ORGANO-MAGNESIUM HALID :-
A Grignard reagent can be prepared in the laboratory by the action of alkyl halid on magnesium metal
in the presences of dry ether (anhydrous diethyl ether).
Mechansim:-
A grignard reagnt can be prepared via a free radical mechanism (in the presences of
diethyl ether medium) which inovlves two steps.
Step 1 : In first step alkyl halid react with magnesium and produced alkyl radical and MgX type
reactive species.
Step 2 : In second step alkyl free radical combine with magnesium and yield grignard
reagent.
ROLE OF ETHER(SOLVENT):-it plays dual role provide
 Medium for the solvent.
 Act as stabilizing phenomenen because oxygen from ether donate its lone pair electron
pair to Mg to complete its octet and make a stable complex or, dimer.
 THF is also used as solvent medium for prepration of RMgX.
Two molecule of diethyle ether comlex
with the Mg atom of grignard reagent.
R X + Mg R.
+ .
MgX
Diethyl Ether
R.
+ .
MgX Diethyl Ether
R MgX

4. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM
NOTE : Grignard reagent cannot be prepared from halid contain acidic group in their halid molecule
e.g.
Grignard reagent will not react with the compound contain acidic hydrogens. (For example H20, ROH,
RNH2,and RCOOH). The acidic hydrogen will first react with the grignard reagent and form an
alkanes.
PHYSICAL PROPERTIES (OF RMgX):-
 Grignard reagent are non volatile colorless solid.
 They are seldom islolted in the free state on account of their explosive nature.
 Therefore,for synthetic purposes grignard reagent are always prepared and used in ether
solution.
REACTIVITY OR CHEMICAL PROPERTIES(OF RMgX):-
 The carbon – magnesium bond in grignard reagent is covalent but highly polar in nature.
 The carbon atom is more electronegative then magnesium.
 The electron of carbon – magnesium bond are drwan toward the carbon atom. As a result the
carbon atom has a partial negative charge and magnesium atom has partial positive charge.
or,
 The alkyl group (R-
) in grignard reagent are electron rich act as carbonion/good nucleopihe or
a good base. They would attack on polarized molecule at the point of electron density.
 Therfore, characteristic reaction of grignard reagnt are :
 Nucleophilic substitution reaction.
 Nucleophilic addition reaction.
-
R MgX
+-

5. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM
APPLICATION OF GRIGNARD REAGENT:-
The basic various application of Grignard reagent are the following:
1) On a reaction with active hydrogen not only provides a method for the synthesis of
alkanes but also forms a basis for the Zerevitinoff determination of active
hydrogen. This is done by measuring the amount of methane (CH4) produced, one
molecule of which indicates the presence of one active (H) atom in the original
compound. Thus this reaction can be used to distinguish primary. Secondary and
tertiary amines (RNH2, R2NH, R3N) by measuring the volume of the gas produced
per mole of the amine.
2) Many organic compounds can be prepared on it by treating with different reagent.
3) The following compound can be synthetically commercially prepared for different
purposes such as hydrocarbon, carboxylic acid, acetone, alky halid, ammines,
alcohols (primary, secondary, tertiary), aldehyde etc.
4) Their treatment with different reagent give different products are as follows :

6. Written BY : AMIR HASSAN OF BS CHEMISTRY DEPARTMENT GPGC MARDAN
EMAIL : AMIRHASSAN741@GMAIL.COM