Use the References to access important values if needed for this question. a. Us
ID: 487340 • Letter: U
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Use the References to access important values if needed for this question. a. Use strain energy increments in the OWL Table Reference (see References button, Strain Energy Increments) to calculate the energy difference between the two chair conformations of the compound below. b. Specify substituent positions (axial or equatoria) in the more stable chair. c. Estimate the percent of the more stable chair at equilibrium at 25°C. (To determine the percent of the more stable chair at equilibrium, first calculate Keg and then use this value to find the percentage. CH3 Answers: a. The energy difference is kJ/mol. b. In the more stable chair The vinylethenyl group is in the position o o The methyl group is in the position c. At 25% the equilibrium percent of the more stable chain conformation is approximately 9 more group attempts remaining Retry Entire Group Submit AnswerExplanation / Answer
1,4 cis means one group takes axial and other takes equitorial
If we had CH3 axial and CH=CH2 equitorial
If CH3 axial , strain energy = 7.3 KJ/mol, If Ch=CH2 is axial then strain energy = 6.2 KJ/mol
energy differnece = 7.3-6.2 = 1.1 KJ/mol
b) Most stable is when we have vinyl group at axial and Methyl group in equitorial position
c) Methyl axial <---> Vinyl axial ,
dGo = Vinyl axial - Methyll axial = 6.2-7.3 = -1.1 KJ/mol = -1100 J/mol
dGo = -RT ln K
-1100 = - 8.314 x 298 ln K ( where T = 25C = 25+273 = 298 K)
K = 1.56 = [Vinyl axial ] /[Methyl axial]
Let initially [Methyl axial ] =1 , then at equilibrium [Methyl axial] = 1-X , [Vinyl axial] = X
Then K = 1.56 = ( X/1-X)
1.56 = 2.56X
X = 0.609,
Most stable conformer is when we have vinyl at axial and Methyl at equitorial , X = 0.609
% of most stable isomer = ( 100 x fraction of isomer where vinyl is at axial)
= ( 100 x 0.609) = 60.9 %
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