How can I explain the mechanism for the acid-catalyzed addition of water to an alkene?

Question

Addison Armstrong · Accepted Answer

Well, you got an olefin, an electron RICH species....

i.e. #RCH=CHR#...and you could add an acid, which we will represent as #D_3O^+#...the which contains electrophilic protons/deuterons... #RCH=CHR + stackrel(+)D-OD_2rarr Rstackrel(+)CH-CH(D)R+D_2O# The hydroxyl function should then react with the electrophilic carbocation. #Rstackrel(+)CH-CH(D)R+OD_2 rarrRCH(OD)-CH(D)R+D^+# And by way of example, we could bubble ethylene gas, #H_2C=CH_2#, thru a solution containing water, and ethanol, and halide salts, and cyanide salts....there would be NO reaction UNTIL we added a source of #H_3O^+#...and this would PROTONATE the olefin to give a formal carbocation, the which would then react with ANY nucleophile present in the solvent (including the solvent itself)...... #Rstackrel(+)CH-CH_2Rstackrel(H_2O,""^(-)C-=N, X^-)rarrRCH(OH)-CH_2R+RCH(C-=N)-CH_2R+RCH(X)-CH_2R#

Sarah Angotti · Answer

undefined The acid-catalyzed addition of water to an alkene follows a mechanism known as the Markovnikov addition. In this process, the alkene undergoes electrophilic addition with a proton (H⁺) from the acid catalyst, forming a carbocation intermediate. The water molecule then attacks the carbocation, leading to the formation of a tertiary alcohol product. The overall reaction proceeds through protonation, carbocation formation, nucleophilic attack, and deprotonation steps.