(a) which tertiary carbocations is more stable, 1-adamant or t-butyl? explain wh
ID: 876445 • Letter: #
Question
(a) which tertiary carbocations is more stable, 1-adamant or t-butyl? explain why it is more stable and tell how your experimental results support this conclusion. (b) which solvent promotes the formation of a carbocations more effectively, 40% ethanol or 80% ethanol? explain. Reactions and Properties RBr + HOROH +HBr and (R 1-adamantyl or t-butyl) HBr +KOH HO + KBr Table 1 Physical properties mol wt mp bp 215.1 118 1-bromoadamantane 2-bromo-2-methylpropane 13701 Note: mp and bp are in 'C: density is in g/ml 2-methylpropane 137.0 -16 73 1.221 DIRECTIONS The alkyl halides must be protected from moisture; be sure that your glass- ware is clean and dry. With your instructor's permission, work in pairs, with one student recording the times and the other adding the KOH solution. Safety 2-Bromo-2-methylpropane is harmful if inhaled or absorbed through the skin, and it may be carcinogenic. Avoid contact and do not breathe its vapors. A. Solvolysis of 1-Bromadamantane in 40% Ethanol Preparation of Solutions. Prepare an indicator blank by measuring 25 mL of a pH 6.9 buffer into a 50-mL Erlenmeyer flask and adding 4 drops of bromthymol blue indicator solution (the blank should be green). Set this flask aside while you prepare the reaction mixture. Measuring [OP-5] as accurately as possible, combine 100 mL of 95% ethanol and 14.5 mL of distilled water in a 50-mL. Erlenmeyer flask. AddExplanation / Answer
Explanation is given below.
(a) t-butyl carbocation will be more stable then 1-adamant.
In tert-butyl carbocation we have 9 hyperconjugation stabilization as opposed to only 6 hyperconjugation possible in case of 1-adamant carbocation. The former has 9 H's attached to the carbons next to the carbocation center, whereas, the later has only 6 H's attached to the carbons next to the carbocation center. This provides extra stability to the tert-butyl carbocation.
(b) Carbocation formation in 40 % and 80 % ethanol solvent system : For SN1 reaction, polar solvents are preferred over non-polar solvents and protic solvents are preferred over aprotic solvents. Since water (H2O) is the protic solvent of the two ethanol and water present here, the higher the concentration of water present in in the mixture the greater would be the rate of carbocation generation. Hence, the reaction would be faster with 40 % ethanol as compared to 80 % ethanol. Note, in the former case, we have more water present and since water is the more polar and protic solvent it would favor the formation of carbocation.
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