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Alcohols & Ethers
(1) Boiling point:
(2) Solubility in water:
As molecular weight increases solubility in water decreases. The lower alcohols are miscible with water. This is due to intermolecular hydrogen bonding between alcohol and water molecules.
Preparation of alcohols
(1) From alkenes
C. By Hydroboration – oxidation process: (Forms anti-markovnikov alcohol, no rearrangement)
(2) From alkyl halides: By nucleophilic substitution reactions
(3) From Grignard reagents
1. Organometallic compounds
Organometallic compounds are the organic compounds in which a metal atom is directly attached to carbon atom through covalent bond or ionic bond.
C – M or C M
(Where C is a carbon atom of an organic molecule and M is a metal atom)
If the metal atom is attached to oxygen, nitrogen. sulphur, etc. then such an organic compound is not regarded as an organometallic compound. The following structural formula do not belong to the family of organometallic compounds.
R-X + Mg → R0 + X⊝ + Mg+ → R⊝ + Mg+ + X⊝ → R-MgX
*(RMgX is only nucheophile)
Note: It should be noted that (CH3)4Si (Tetramethylsilane, TMS) is also not an organometallic compound because silicon is a nonmetal.
Most important examples of organometallic compounds are Grignard reagents. In Griganard reagent, the carbon and magnesium atoms are bonded with each other through polar covalent bond and magnesium atom is attached to halogen by ionic bond.
C – MgX (Functional part of a Grignard reagent molecule)
In organometallic compounds, the metal atom can be bonded to carbon of a hydrocarbon radical (Saturated, unsaturated, aliphatic, alicyclic or aromatic) or carbon atom of a heterocyclic radical. Some examples are given below.
ii. Alkynyl Grignard reagent
CH3 ≡ C – CH2 – MgX
Alicyclic Grignard reagent
Aromatic Grignard reagent
C6H5CH2MgCl (Benzylmagnesium halide)
Heterocyclic Aromatic Grignard reagent
(Pyridine -4-magnesium halide)
Heterocyclic Nonaromatic Grignard reagent
In a Grignard reagent. X is generally Cl, Br or I (Halogen). Order of reactivity is as follows:
RMgl > RMgBr > RMgX
Ether is used as a solvent because it is a Lewis base that donates its lone pair of electrons to electron-deficient magnesium atom, therefore providing stability to the Grignard reagent by completing the octet on magnesium atom.
1.3 Reactivity of grignard reagents.
It has been found out by estimation that there is 35% ionic character in carbon-magnesium bond of Grignard reagent. Therefore, there is a tendency of forming carbon ion by heterolysis of this polar coordinate bond as follows.
The carbanion (a nucleophile) formed as shown above, attacks the positively, charged electrophilic centre of other compound. Therefore. It can be said that if a Grignard reagent is regarded as the substrate, then electrophile displaces MgX, i.e., electrophilic substitution (ESR) reaction takes place.
If Grignard reagent is regarded as the attacking reagent, then the nucleophilic carbonion of Grignard reagent will attack on the other compound taken as substrate.
1.4 Reactions of Grignard reagent
On having same hydrocarbon radical, the order of reactivity of Grignard reagents will be as follows:
RMgI > RMgBr > RMgCl
Grignard reagent gives the following two type of reactions.
(i) Acid base reaction
(ii) electrophonic-nucleophilic reaction
Table: IUPAC Nomenclature of Acid derivatives
If the substituent is a second carboxyl group, we have a dicarboxylic acid. For example
Physical properties of acids and acid derivatives
1. Boiling point :
CH3 CH2 CH2 OH CH3 CH2 CH2 OH
The high boiling point of carboxylic acids is the result of formation of stable hydrogen –bonded dimer
Carboxylic acids form hydrogen bonds with water and the lower molecular –weight carboxylic acids (up to 4 carbon atoms) are miscible with water.
Acid derivatives (esters, acid chlorides, anhydride, nitriles and amides) are soluble organic solvents such as alcohols, ethers, chlorinated alkanes and aromatic hydrocarbons.
Methods of preparation of carboxylic acids
Synthese of carboxylic acids by the carboxylation of grignard reagents :
Synthesis of Carboxylic acids by the hydrolysis of nitriles Mechanism :
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