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Analysis of Butane Interactions and Cyclohexane Derivatives Conformations

This lecture delves into the conformational analysis of butane and cyclohexane derivatives, focusing on gauche and eclipsed interactions in different structural forms. It discusses the energy differences between these interactions and the notation of interactions in butane configurations. A significant portion covers the preferred conformations of cis- and trans-4-t-butylcyclohexan-1-ol, and 1,2- and 1,3-dimethylcyclohexane, including their optical activity. Practical exercises include drawing conformations and converting between Newman and Fischer projections while assigning R/S configurations.

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Analysis of Butane Interactions and Cyclohexane Derivatives Conformations

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  1. Lecture 4

  2. In chain form, 6 gauche butane interactions ( units) In boat form, 4 gauche butane interactions (units) + 2 eclipsed butane interactions (units) + Bowsprit – Flagpole interaction. • E boat -  E chain == ( 2 eclipsed butane – 2 gauche butane) + B.F. Interaction == 2 * 4.0 - 2* 0.9 + B.F. Interaction == 6.2 + B.F. Interaction

  3. Drawing the preferred conformations of cyclohexane derivatives : Cis – 4-t-butyl cyclohexan-1-ol Trans – 4-t-butyl cyclohexan-1-ol Steps : (1) for cis both groups should be a or b for trans one group is a and the other b (2) Now draw the cyclohexane chair : (3) Place the bigger group in the equatorial position. (4) Place the other group axial or equatorial according to cis or trans

  4. Cis and Trans 1,2 – Dimethylcyclohexane : A is the flipped form of B and vice versa. C is the mirror image of B C is same as A A & B are of same energy, so they are present as 50 : 50 mixture and are interconvertible through a low energy barrier. Thus, cis 1,2 – dimethylcyclohexane exists as a nonresolvable dl – pair.

  5. Trans 1,2- dimethylcyclohexane A & C are different. Qn : Draw the preferred conformations of cis and trans 1,3 – dimethyl cyclohexane. Comment on it optical activity.

  6. Qn: Write down the preferred conformations of cis and trans 4-t-butyl-cyclohexan-1-ol. Which compound will undergo faster oxidation to the corresponding ketone with chromic acid? Qn: Assign R/S configuration to the following molecule. Qn. Convert the following Newman Projection into Fischer Projection Formula and then assign R/S.

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