Chem 125 Lecture 4/11/07 Projected material This material is for the exclusive use of Chem 125 students at Yale and may not be copied or distributed further. It is not readily understood without reference to notes from the lecture.
Mechanism for Acid-Catalyzed Hydrolysis of “Ketal” RO CH 2 + H HOH : : RO CH 2 + HROH RO-CH 2 + HO RO CH 2 + H First remove RO, and replace it by HO (S N 1). HO RO CH 2 Now remove second RO and H (E1) + H : HO RO CH 2 + H RO=CH 2 + cation easily formed; unusually stable ROH H-O-CH 2 + O=CH 2 ROH RO CH 2 O H H Overall Transformation: Ketal Carbonyl “Hemiketal” (or E2 with base) No S N 2 with base! protecting group for C=O, like t-Bu ether for ROH.
gem-diol stability pp
Cl 3 C-CH(OH) 2 Cl 3 C-CHOCl 3 C-CH 2 OH
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