Identificação de Grupos Saindo em Reações Químicas

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Solutions to Problems 183 CH₃ CH₃ H H H₂O, DMF H H X X S B C (Partial structure; X = unidentified leaving group) How do we identify the leaving groups X? Look at the precursors to B: an acyclic compound A with the formula C₆H₁₄O₂, and two equivalents of a sulfonyl chloride, CH₃SO₂C1. The simplest solution is to assume X is the sulfonate CH₃SO₃-, and A is the dialcohol corresponding to B. Thus, we arrive at these structures: CH₃ CH₃ H H H H HO OH O₃SCH₃ A B P.S. The final product of the sequence is a (cyclic) sulfone. 61. Everything goes well until the last step. Then-disaster! OH + + H HCI + Strained rings are particularly good candidates for carbocation rearrangement if the strain can be relieved in the process. 62. Use thionyl chloride, SOCl₂, for the alcohol to chloroalkane conversion. Using thionyl chloride with secondary alcohols shifts the mechanism from SN1 to and, therefore, removes carbocation formation from the process. No carbocation, less risk of rearrangement. 63. The first reaction converts the alcohol and the tosyl chloride into a tosylate. In this process the alcohol is the nucleophile, displacing chloride from sulfur. There is no chemical change at the bond of the alcohol, and, therefore, no change in the (R) chirality at of the alcohol: CH₃ (R)-CH₃CH₂CH₂CH₂CHDOH S CH₃ -HCI (R)-1-Deuterio-1-pentanol tosylate The second step is displacement of the tosylate group by the nucleophile ammonia. The reaction occurs at a primary carbon, so it may be safely assumed to proceed by the SN2 mechanism. Therefore in this step the bond of the original alcohol molecule breaks, with inversion, to give a product with the (S) configuration at