QQuestionChemistry
QuestionChemistry
" Identify what reagents you would use to achieve each transformation:
(a) Conversion of 2 -methyl- 2 -butene into a secondary alkyl halide
(b) Conversion of 2 -methyl- 2 -butene into a tertiary alkyl halide
(c) Conversion of cis- 2 -butene into a meso diol
(d) Conversion of cis- 2 -butene into enantiomeric diols"
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Answer
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Step 1
\text{CH}_3-\text{C}(=\text{CH}_2)-\text{CH}(\text{CH}_3)_2 + \text{HX} + \text{ZnX}_2 \rightleftharpoons \text{CH}_3-\text{C}(\text{X})-\text{CH}(\text{CH}_3)_2 + \text{ZnX}_2\text{H}^+
To convert 2 -methyl- 2 -butene into a secondary alkyl halide, we can carry out a substitution reaction using a halogen acid (like hydrochloric acid, HCl) and a Lewis acid catalyst (like zinc chloride, ZnCl2). The halogen acid donates a proton to the double bond, activating it for nucleophilic attack. The Lewis acid catalyst then coordinates with the halogen atom, increasing its electrophilicity. A halogen ion (Cl-, Br-, or I-) can then attack the double bond, forming a new carbon-halogen bond and creating a secondary alkyl halide.
Step 2
\text{CH}_3-\text{C}(=\text{CH}_2)-\text{CH}(\text{CH}_3)_2 + \text{t-BuCl} \rightleftharpoons \text{CH}_3-\text{C}(\text{Cl})-\text{C}(\text{CH}_3)_3
To convert 2 -methyl- 2 -butene into a tertiary alkyl halide, we can use a similar substitution reaction as in part (a), but this time we will use a tertiary halogen acid (like tert-butyl chloride, t-BuCl) instead of a halogen acid. The tertiary halogen acid can donate both a proton and a halogen ion in a single step, leading to the formation of a tertiary alkyl halide.
Final Answer
(a) HCl and ZnCl^2 (b) t-BuCl (c) Peracid or H^2O^2 -based system (d) Sharpless asymmetric epoxidation
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