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Hydrocarbons

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Hydrocarbons PDF Notes, Important Questions and Formulas

Aromatic Compound

Some important aromatic compound with their common names.

Formula

Name

Formula

Name

Toluene

(bp 111°C)

Benzaldehyde

(bp 178°C)

Phenol

(mp 43°C)

Benzoic acid

(mp 122°C)

Aniline

(bp 184°C)

Benzonitrile

(bp 191°C)

Acetophenone

(mp 21°C)

Ortho-xylene

(bp 144°C)

 
IUPAC Name of Substituted phenol and benzoic acid.
     
Electrophilic Aromatic Substitution Reaction

A reaction energy diagram for the electrophilic bromination of benzene. The reaction occurs in two steps and releases energy.

 
Some Electrophilic Aromatic substitution reactions:

  1. Ortho- and para-directing activators: Groups like –OH ad –NH2 present on a ring direct an electrophile, E+, to ortho or para position and they react faster than benzene.
  2. Ortho- and para-directing deactivators: Helogens present on a ring direct an electrophile, E+, to ortho or para positions, and they react slower than benzene.
  3. Meta-directing deactivators: Groups containing a carbonyl (C = O) or a –CN group direct an electrophile, E+, to the meta positions, but they react slower than benzene.
    No meta-directing activators are known. Figure 5.8 shows how the directing effects of the groups correlate with their reactivities. All meta directing groups are deactivating and most ortho-and para-directing groups are activating. The halogens are unique in being ortho and para directing and deactivating.

 

 

Figure Substituent effects in electrophilic aromatic substitutions. All activating groups are ortho-and para-directing, and all deactivating groups other than halogen are meta-directing. The halogens are ortho and para-directing deactivators.





Hydrocarbon

ALKANE

Alkane are the saturated non polar hydrocarbon having general formula CnH2n+2.
Hydrocarbon – Those organic compounds which contain only carbon and hydrogen atoms are known as hydrocarbons.
General method of preparation

  • By catalytic reduction of alkenes and alkynes



    Hydrogen → Addition of H2 to unsaturated bond

    Hydrogenation is of two kind

  1. Heterogeneous and b.  Homogeneous
    (a) Heterogeneous →It is two phase hydrogenation the catalyst id finely divided metal like Ni, Pt or Pd and a solution of         alkene.

    (b) Homogeneous→ It is one phase hydrogenation both catalyst and alkenes area solution. In this hydrogenation catalyst       are organic complex of transition metal like Rh or Ir.

    Hydrogenation is exothermic, qualitative and during the hydrogenation, total heat evolved to hydrogenate one mole of unsaturated compound is called heat of hydrogenation. Heat of hydrogenation is the measurement of stability of isomeric alkenes.

    begin mathsize 12px style stability space of space alkene  ∝ fraction numerator 1 over denominator Heat space of space hydrogenation space end fraction end style

  • From alkyl halide

    A.  From organometallic compound→
              δ- +δ

    Compound having C-M bond.
    (M → metal)

    (i)  By wurtz reaction

begin mathsize 12px style table attributes columnalign left end attributes row cell 2 straight R minus straight X plus 2 Na rightwards arrow with dry space ether on top straight R minus straight R plus 2 NaX end cell row cell straight R minus straight X plus straight R apostrophe minus straight X rightwards arrow from ether left parenthesis dry right parenthesis to Na of straight R minus straight R comma straight R minus straight R apostrophe comma straight R apostrophe minus straight R apostrophe end cell end table end style
Mechanism →Two mechanisms are suggested


  1. Ionic mechanism

    2Na→2Na+2e







  2.  Free radical mechanism

    begin mathsize 12px style stack Na rightwards arrow Na with                 circled plus on top plus straight x with blank to the power of ⊖ on top
straight R minus straight X plus straight e with blank to the power of ⊖ on top rightwards arrow straight R to the power of • plus straight X to the power of ⊖ end style

    R+R→R-R


    Note:

    The alkyl halide should be 1° or 2°, with 3° R-X SN2 and free radical coupling is not possible due to steric hinderance so in that case elimination or disproportionate is possible.

    In the ionic mechanism alkyl sodium begin mathsize 12px style straight R with blank to the power of ⊖ on top Na with circled plus on top end style gives begin mathsize 12px style straight R with blank to the power of ⊖ on top end style strong base as well as nucleophilic
    which gives SN2 with R-X, ether should be dry otherwise, if moisture is present then begin mathsize 12px style straight R with blank to the power of ⊖ on top end style forms R-H instead of R-R with H2O
    (ii)  By  G. R begin mathsize 12px style table attributes columnalign left end attributes row cell table row straight R minus straight X end table end cell row cell table row cell 1 to the power of degree end cell cell 2 to the power of degree end cell cell 3 to the power of degree end cell end table table row cell rightwards arrow from ether to Mg of end cell row blank end table table row RMgx row blank end table end cell end table end style

    RMgX + H congaing compound→ R – H



    (iii)    By corey house alkane synthesis

    Mechanism:

    R­­2 CuLi is the source of R

R2 CuLi do not react with –NO2, -CN, >C=O etc.




 







 

 

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