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Organic Compounds Containing Oxygen

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Organic Compounds Containing Oxygen PDF Notes, Important Questions and Formulas

Alcohols & Ethers

ALCOHOL

 

Physical Properties

(1)   Boiling point:

  1. Alcohols show increase in boiling point with increase in molecular weight amongst homologues.
  2. Alcohols have higher boiling point than hydrocarbons of the same molecular weight. The reason for higher boiling point is the intermolecular H-bonding present in alcohols.

(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

  1. By acid catalyzed hydration of alkenes: Formation of carbocation intermediate (Markovnikov addition, rearrangement possible)
    General reaction
    begin mathsize 12px style table attributes columnalign left end attributes row cell straight R minus CH equals CH subscript 2 text   end text rightwards arrow from Markonikoff apostrophe straight s text  addition end text to conc. straight H subscript 2 SO subscript 4 of straight R minus CH minus CH subscript 3 text   end text rightwards arrow with Boiling text  H end text subscript 2 straight O on top straight R minus CH minus CH subscript 3 end cell row cell text      end text Alkene text                                                         |                                               | end text end cell row cell text                                                                       OSO end text subscript 3 straight H text                                     OH end text end cell row cell text                                                                                                                    Alcohol end text end cell end table end style
    e.g.


  2. By Oxymercuration - demercuration process :
  1. Oxymercuration involves an electrophilic attack on the double bond by the positively charged mercury species. The product is a mercurinium ion, an organometallic cation containing a three-membered ring.

  2. In the second step, water from the solvent attacks the mercurinium ion to give (after deprotonation) an organomercurial alcohol.
  3. The third step is demercuration to remove the Hg. Sodium borohydride (NaBH4, a reducing agent) re-places the mercuric acetate fragment with hydrogen.
    General reaction


    e.g.

 

C. By Hydroboration – oxidation process: (Forms anti-markovnikov alcohol, no rearrangement)
General reaction


begin mathsize 12px style straight R minus Ch equals CH subscript 2 text    end text rightwards arrow from left parenthesis ii right parenthesis text  H end text subscript 2 straight O subscript 2 comma text   end text NaOH to left parenthesis straight i right parenthesis text  BH end text subscript 3. THF of text  R-CH end text subscript 2 minus CH subscript 2 minus OH end style

e.g.

 

(2)   From alkyl halides: By nucleophilic substitution reactions

  1. By SN2 mechanism (second-order substitution) : It is given by primary (and some secondary) halides
    General reaction:
    R-CH2-Br begin mathsize 12px style rightwards arrow from straight H subscript 2 straight O to KOH of end style R-CH2-OH
    e.g.
    (CH3)2CHCH2CH2-Br begin mathsize 12px style rightwards arrow from straight H subscript 2 straight O to KOH of end style (CH3)2CHCH2CH2-OH
  2. By SN1 mechanism : It is given by tertiary and some secondary halides
    General reaction:


    e.g.

(3)   From Grignard reagents

  1. From air
    A Grignard reagent may be used to synthesize an alcohol by treating it with dry oxygen and decomposing the product with acid:
    General reaction
    RMgX begin mathsize 12px style rightwards arrow with straight O subscript 2 on top end style RO2MgX  begin mathsize 12px style rightwards arrow with RMgX on top end style 2ROMgX begin mathsize 12px style rightwards arrow with straight H subscript 2 straight O to the power of plus on top end style 2ROH
    e.g.
    C2H5MgBr begin mathsize 12px style rightwards arrow with straight O subscript 2 on top end style C2H5O2MgX begin mathsize 12px style rightwards arrow with straight C subscript 2 straight H subscript 5 MgX on top end style 2C2H5OMgX begin mathsize 12px style rightwards arrow with straight H subscript 2 straight O to the power of plus on top end style 2C2H5OH + MgBr(OH)
  2. From ethylene oxide
    Addition of Grignard reagent to ethylene oxide gives a primary alcohol (with two carbon atoms added)
    General reaction


    e.g.

  3. From carbonyl compounds: Nucleophilic addition to the carbonyl groups by Grignard reagent

    General reaction





    Grignard Reagent


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.
For example
                     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.

begin mathsize 12px style straight R minus straight X rightwards arrow with Mg divided by dry space ether on top RMgX left parenthesis Grignard space reagent right parenthesis end style

R-X + Mg → R0 + X+ Mg+ → R+ Mg+ + X→ R-MgX

*(RMgX is only nucheophile)

Reason

 
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.

  1. Saturated Aliphatic Grignard reagent

    R-MgX (Alkylmagnesium halide) CH3-Mgl (Methylmagnesium iodide)


  2. Unsaturated Aliphatic Grignard reagent

    i. Alkenyl Grignard reagent

       1 CH2 = CH – CH2 - Mgx (Allylmagnesium halide)

    ii. Alkynyl Grignard reagent

        CH3 ≡ C – CH2 – MgX
      (Propargylmagnesium halide)

  3. Alicyclic Grignard reagent


    (Cyclohexylmagnesium halide)

  4. Aromatic Grignard reagent


    (Phenylmagnesium halide)

    C6H5CH2MgCl (Benzylmagnesium halide)

  5. Heterocyclic Aromatic Grignard reagent


    (Pyridine -4-magnesium halide)

  6. Heterocyclic Nonaromatic Grignard reagent


    (Piperidene-4-magnesium halide)

    In a Grignard reagent. X is generally Cl, Br or I (Halogen). Order of reactivity is as follows:

    RMgl > RMgBr > RMgX


    1.2  Preparation

    begin mathsize 12px style RX plus Mg rightwards arrow from Ether to Dry straight space and space pure of RMgX end style

    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



    Carboxylic acid

    Introduction:





    Table: IUPAC Nomenclature of Acid derivatives















    Dicarboxylic acids:

    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

     

    Propionaldehyde, bp91℃





     Propionaldehyde, bp49

    The high boiling point of carboxylic acids is the result of formation of stable hydrogen –bonded dimer




    Solubility:

    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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