Q2. Answer any TWO of the following parts: (a) Draw the two main conformations that exist for cyclohexane. Explain clearly why one conformer is more stable than the other. Using cis-1-ethyl-3-methylcyclohexane, as an example, explain how ring flipping occurs. Draw both conformers of cis-1-ethyl-3-methylcyclohexane and explain clearly which one predominates. (b) What is polarimetry? The specific rotation of (R)-carvone is - 61°. A chemist prepared a 750 mg mixture of (R)-carvone and its enantiomer in 10 ml of ethanol and placed the solution in a 10 cm polarimeter cell. The observed rotation was - 4.125°. Calculate the specific rotation for the above mixture. What is meant by enantiomeric excess? Then determine the % enantiomeric excess (% ee) in the mixture. (i) (ii) (iii) What % of the mixture is (R)-carvone and (S)-carvone?

(a) What is the IUPAC name for the following molecule (including absolute configurations if required)? (b) Draw the Newman projections looking down the C3-C4 bond that represent all the three staggered conformations for the molecule shown above. (c) Given that the strain energies below, calculate the strain energies for each conformer and identify which is the most stable. Gauche interaction Strain Energy HOCH3 0.0 kJ mol- HOCH;CH; |0.4 kJ mol- 3.8 kJ mol- | 4.3 kJ mol- CH;CH3 CH;CH2CH3 |CH2CH; CH2CH; 4.6 kJ mol- Newman Projection of Conformer 1 Strain Energy of Conformer 1 Newman Projection of Conformer 2 Strain Energy of Conformer 2 Newman Projection of Conformer 3 Strain Energy of Conformer 3

• Question 3: a) Draw the three staggered and three eclipsed conformations that result from rotation around the designated bond using Newman projections. b) Label the most stable and least stable conformation. rotation here H CH3 C CH₂CH3 CH3

Give your view on boat conformation of cyclohexane ?