8Chapter 04

cl h fast bimolecular fast h ch33c o h tert

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Unformatted text preview: . H tert-Butyloxonium ion Dr. Wolf's CHM 201 & 202 4- 58 Step 1: Proton transfer Step 1: Proton transfer (CH3)3C .. O: + H .. Cl: .. H fast, bimolecular fast, H + (CH3)3C O : + H tert-Butyloxonium ion Dr. Wolf's CHM 201 & 202 .. – : Cl: .. Species formed in this step (tertbutyloxonium ion) is an intermediate in an intermediate the overall reaction. 4- 59 Potential energy diagram for Step 1 Potential energy diagram for Step 1 Potential δ+ (CH3)3CO Potential Potential energy Cl H (CH3)3COH + H—Cl Reaction coordinate Dr. Wolf's CHM 201 & 202 H δ− + (CH3)3CO C H + Cll – H 4- 60 Step 2: Carbocation formation Step 2: Carbocation formation Dissociation of the Dissociation alkyloxonium ion involves alkyloxonium H bond-breaking, without + any bond-making to any (CH3)3C O : compensate for it. It compensate H has a high activation energy and is slow. energy slow slow, unimolecular H (CH3)3C + + tert-Butyl cation Dr. Wolf's CHM 201 & 202 :O: H 4- 61 Step 2: Carbocation formation Step 2: Carbocation formation H A single molecule reacts in this step; therefore, it is unimolecular. + (CH3)3C O : H slow, unimolecular H (CH3)3C + + tert-Butyl cation Dr. Wolf's CHM 201 & 202 :O: H 4- 62 Step 2: Carbocation formation Step 2: Carbocation formation H + (CH3)3C O : The product of this step is a carbocation. It is an intermediate It intermediate in the overall process. (CH3)3C + H slow, unimolecular H + tert-Butyl cation Dr. Wolf's CHM 201 & 202 :O: H 4- 63 Potential energy diagram for Step 2 Potential energy diagram for Step 2 Potential δ+ (CH3)3C Potential Potential energy + (CH3)3CO H O δ+ H + (CH3)3C + H2O H H Reaction coordinate Dr. Wolf's CHM 201 & 202 4- 64 Carbocation Carbocation R + C R R The key intermediate in reaction of secondary The and tertiary alcohols with hydrogen halides is a carbocation. carbocation. A carbocation is a cation in which carbon has 6 valence electrons and a positive charge. Dr. Wolf's CHM 201 & 202 4- 65 Figure 4.9 Structure of tert-Butyl Cation. Figure 4.9 Structure of ttert-Butyl Cation. ert Figure Figure tert CH3 H3C + C CH3 Positively charged carbon is sp2 hybridized. Positively sp hybridized. All four carbons lie in same plane. Unhybridized p orbital is perpendicular to Unhybridized plane of four carbons. plane Dr. Wolf's CHM 201 & 202 4- 66 Step 3: Carbocation capture Step 3: Carbocation capture Step Bond formation between the positively charged .. – (CH3)3C + + : Cl: carbocation and the carbocation .. negatively charged chloride ion is fast. fast fast, bimolecular (CH3)3C .. Cl: .. tert-Butyl chloride Dr. Wolf's CHM 201 & 202 Two species are involved in this step. involved Therefore, this step iis bimolecular. s bimolecular 4- 67 Step 3: Carbocation capture Step 3: Carbocation capture (CH3)3C + + .. – : Cl: .. This is a Lewis acidLewis base reaction. The carbocation is the Lewis acid; chloride ion is the Lewis base. fast, bimolecular (CH3)3C .. Cl: .. tert-Butyl chloride Dr. Wolf's CHM 201 & 202 The carbocation is an electrophile. electrophile Chloride ion is a nucleophile. 4- 68 Step 3: Carbocation capture Step 3: Carbocation capture + (CH3)3C + Cl – Lewis acid Lewis base Electrophile (CH3)3CCl Nucleophile Dr. Wolf's CHM 201 & 202 4- 69 Potential energy diagram for Step 3 Potential energy diagram for Step 3 δ+ (CH3)3C δ− Cl δ− Potential Potential energy (CH3)3C+ + Cll– C (CH3)3C—Cl Reaction coo...
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This document was uploaded on 01/03/2012.

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