Chem210-1 F06 Ex3 p04a

Chem210-1 F06 Ex3 p04a - For compounds'A and'B that...

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4. Compound 'A' below reacts at a certain rate with aqueous acid under specific conditions of concen- tration and temperature. Under exactly identical conditions, compound 'B' reacts about two-and-a- half times faster than 'A', and (again under identical conditions), compound 'C' reacts about 6,000 times faster than 'A'. a) Provide the structure of the product expected for the reaction of 'C' with aqueous acid (3 points) b) Explain BRIEFLY why 'C' reacts so much more rapidly than 'A' (or "B', for that matter). BE CONCISE and SPECIFIC. (6 points) c) Explain BRIEFLY why 'B' reacts a bit more rapidly than 'A' . Again, BE CONCISE and SPECIFIC. (6 points) C C CH 3 H H 3 C H C C H CH 3 H 3 C H C C CH 3 CH 3 H 3 C H compound 'A' compound 'B' compound 'C' H 2 C C CH 3 CH 3 H 3 C OH The slow step in hydration is protonation of the alkene to give a carbocation.
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Unformatted text preview: For compounds 'A' and 'B' that carbocation is secondary; for compound 'C' it's tertiary. The tertiary carbocation will be lower in energy than a secondary, and so the transition state leading to it will be lower in energy as well, so that the activation energy leading to that carbocation should be lower than that generated from 'A' or 'B'. Protonation of both 'A' and 'B' gives the same carbocation; however, since 'B' is less stable than 'A' ( cis relative to trans alkene), 'B' will be closer in energy to the transition state leading to that carbocation. Thus 'B' will have a lower activation energy than 'A' in hydration - it will react faster...
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