Rearrangement carbocation intermediate trapped with nucleophiles

Carbocation intermediates can be trapped by nucleophiles in what is known as an 8 1 reaction. An 8 1 reaction proceeds by ionization to a planar carbocation containing an sp hybridized carbon, follows first-order kinetics, and proceeds with racemization of a chiral center. Carbocations are subject to rearrangement to a more stable cation via 1,2-hydrogen or alkyl shifts. 

Most 8 2 reactions are faster in aprotic solvents and slower in protic solvents. Water tends to promote ionization. In pro-tic media, particularly aqueous media, ionization of tertiary halides occurs to give a carbocation intermediate (more slowly with secondary halides) 9,10,11,12,49, 55,69, 70, 77,86. Carbocation intermediates can be trapped by nucleophiles in what is known at an 8 1 reaction. An 8 1 reaction proceeds by ionization to a planar carbocation containing an sp hybridized carbon, follows first-order kinetics, and proceeds with racem-ization of a chiral center. Carbocations are subject to rearrangement to a more stable cation via 1,2 hydrogen or alkyl shifts 24, 25, 26, 27, 29, 50, 65, 67, 76, 77, 78, 79, 80, 81, 83, 84, 85,87,88, 89. A variety of nucleophiles can be used in the substitution reactions, including halides, alkoxides, amines, phosphines, azides, cyanide, acetylides, and enolate anions 2,3,13,14,36,62,63,88, 89,105. 

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