Pinacol-Pinacolone Rearrangement Reaction

By -
Pinacol-Pinacolone Rearrangement  Reaction 

 It involves  acid catalysed  dehydration  of substitution  vicinal diols(pinacol),followed by the rearrangement  of the carbon skeleton  to form ketones. Such rearrangement  are known  as Pinacol pinacolone rearrangement  Reaction or simple pinacol rearrangements.


Mechanism :
this rearrangement  involves following  steps:



Step1, involves protonation of that -OH group, which on elimination  of water molecule gives most stable carbocation. In step 2 carbocation undergoes a 1,2-dimethyl shift to the electron-deficient carbon to generate protonated ketone. In some cases the two steps mentioned above may take place simultaneously,  The attachment  of the migrating group helps to expel the molecule of water. It is important  to remember  that the migrating group does not break away from the carbon it is leaving  untill it attached itself to the electron deficient  carbon as shown below :

Unsymmetrical  pinacols in which the substituent attached  to the hydroxyl bearing carbon are different  the product  obtained  is determined  by the loss of OH as H2O, to give more stable carbocation and thereafter the migration  of the group to carbocation. the preferential  order of migratory aptitude  is found to be :



Popular posts from this blog

Organic Photochemistry Part I

By -
Image
Organic Photochemistry Part I Learning Objectives:   In this unit we shall learn about the  i) Basic Principles of Photochemistry. ii). Several photophysical processes . iii). Photochemical reactions of a few classes of organic compounds. INTRODUCTION Classical Chemistry : It involves the reactions of molecules in their ground electronic states. Photochemistry : It involves the reactions of molecules in excited electronic states.  Organic photochemistry is the study of reactions that occur through excited states of organic molecules produced by the absorption of electromagnetic radiation in the UV-Vis region. Classical Chemistry & Photochemistry There are a few advantages of photochemistry over classical chemistry. 1.In photochemistry selective activation of individual reactant in a mixture of number of reactant is possible. 2.There is an activation energy requirement for every chemical reaction. However if the activation energy is very high, the desired reaction ca...
Read more

Interface-Lippmann equation

By -
Image
  Thermodynamics explaination of electrified interface-Lippmann equation 1.Consider electrode/ electrolyte interface as closed system where no matter leaves or enter in it, then    dU =TdS-W TdS=Q= Heat produced/supplied reversibly W= Work carried out reversibly.  2.Again consider it as an open system, matter can exchange between and surrounding .Let us introduce a mol of i species , the chemical potential on the system is μi  dni is the change of the number of moles, then work done = - μidni dμ= TdS-W-∑μidni ∑μidni= work done required to expel dni of species i The work done in the metal/solution interface (MI/S) are due to (a) volume expansion PdV (b) increase of surface area dA , the corresponding increase of interfacial tension ν. dA 3. Changing the external source of electricity for altering the charge on the metal by dq' M is  MI∆S φ.dq'M MI∆S φ=V, MI∆S φ= interfacial tension, V=applied potential dU=TdS-PdV- νdA - MI∆S φ.dq'M - ∑μidni…….(1) Each ter...
Read more

BUTLER- VOLMER EQUATION

By -
Image
  BUTLER- VOLMER EQUATION: Dependence of electrochemical reaction rate on overpotential. The electrode/solution current may be cathodic or anodic according to the flow of electrons which can measure the sign of overpotential i.e deviation from the equilibrium condition the two partial current densities are equal in magnitude and opposite in direction.i.e      η(overpotential) = ∆φ-∆φe , ∆φ = potential difference observed by adjusting the outside potential source for the change in current flow.     ∆φe = potential difference at equilibrium There will be polarization i.e potential variation from equilibrium     icath = ianod , at equilibrium. If icath = ianod = i 0  r1 = rate of M n+ formation (i cath)  r2=rate of M formation ( i anod)   i 0 = exchange current density                  icath > ianod          r2>r1, if E0 for (M n+ /M) at equilibriu...
Read more