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Showing posts with label REACTION MECHANISM:. Show all posts
Showing posts with label REACTION MECHANISM:. Show all posts

Friday, February 28, 2020

Why is dimethylformamide (DMF) a useful solvent?

DMF, HCONMe2 , is an aproric solvent (has no H for H-bonding) with a moderately high dielectric constant and a high dipole moment. Thus, although it dissolves many ionic compounds, DMF does not do so by forming  H-bonds with the anions. The salts are dissolved, chiefly through solvation of the cation by attraction to the end  of the C-O dipole. The + end of the dipole is shielded within the molecule and can solvate the anion very weakly, if at all.

Why not peroxide effect observed in case of addition of HCl or HI with alkene but it observed with HBr only?

The peroxide effect is not noted in the case of HCI or Hl. This is due to the fact that HCI bond is too strong to be broken to produce free radicals (430.5 kJ mol-1) than the HBr bond (363.7 kJ mol-1). Hl has a lower bond energy (296.8 kJ mol-1) and in case of the addition of HI although H-I bond is easily broken by homolysis, but the iodine atoms so produced immediately react to form iodine molecules rather than attacking the double bond of carbon atom in alkene. 
           °CH3 + HI -->. CH4 +  I°
             I° + I°---> I2

Tuesday, February 11, 2020

What is regioselective reactions explain with example?

The chemical reaction which give two or more different product and these different products are structural or constitutional isomers  to each other but of the isomer is major product , such type of reactions are also called "regioselective".


What is the stereospecific reaction explain with example ?

The chemical reaction in which a stereoselective reactant gives another stereoselective product called Stereospecific reaction for example trans addition of HBr with with but-2-ene give 92% meso-product but cis but-2ene give almost l00%(dl)/ racemic mixture. The sterespecificity of the addition can be explained in terms of a bridged structure in analogy to the bridged bromonium ion in the ionic addition of HBr to alkenes.


Saturday, February 8, 2020

What is the effect of Inversion on basicity of amines?

The rate of nitrogen inversion also correlates with, among other things, hybridization. But in cases where these "other things", such as ring constraints, limit nitrogen inversion, then the rate of nitrogen inversion may not correlate with hybridization. So the rate of nitrogen inversion does not always correlate with hybridization and is therefore not a good indicator of lone pair "availability".

 It is clear that basicity of amines reduced by inversion of amines.

Related Questions:

How to write the mechanism of ring expansion in organic chemistry?

  1. How to write dehydration and ring expansion mechanism of 1-(1-cyclopentyl) methanol?
  2. How to write dehydration and ring expansion mechanism of Tetrahydrofurfuryl alcohol?
  3. How to write dehydration and ring expansion mechanism of 2-cyclopentylethanol?
  4. Write the Dehydration and ring expansion mechanism of following alcohol:
  5. Write Dehydration and ring expansion mechanism of 1-cyclobutylethanol in the presence of con H2SO4.
  6. Explain the ring expansion mechanism of Bicyclic 1,2-Diols which undergoes pinacol pinacolone mechanism?
  7. Explain Dehydration and ring expansion mechanism of 1-(1-Methylcyclopentyl)ethan-ol?
  8. Write the major and minor product of hydration of 1 -Methylcyclopent-1-ene in acidic medium?
  9. Write the major and minor product of hydrohalogenation of 2-Methylbut-1-ene in acidic medium?
  10. To synthesize 2, 3-dimethylbut-1-ene in the better yield dehydrohalogenation of 2, 3-dimethyl-1-bromobutane is preferred over dehydration of 2, 3-dimethylhutan-1-ol. Why ?
  11. Why dehydration proceeds in acid but not in base?
  12. Why alcohols do not undergo base induced dehydration in the same way that alkyl halides are dehydrohalogenated ?
  13. How can write dehydration mechanism of 1,2,3-Trihydroxymethylcyclopropane into Benzene in acidic medium?

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Thursday, February 6, 2020

Why tetraalkylammonium ion ((CH3)4 N+) is neither an electrophile nor a nucleophile and H3O+ is not nuclephile but electrophile alihough it contains a lone pair of electrons.


There is no electron pair on nitrogen Moreover nitrogen cannot accept electron pair since all its orbitals are fully occupied. Therefore, it can neither act as electrophile nor as nucleophile. 

Related Questions:


Why does not carbon form C+4 or C-4 ions? Explaine.

To form C4+ions , four electrons are to be removed from carbon, which require a high value of ionization  energy. It is not available under ordinary conditions. 
To form C4-, four electrons are to be added to carbon, which require a very high energy to overcome repulsions between C- and the electrons being added. That why carbon does not form C+4 and C-4 ions.

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