Question

Two methyl groups Distance between methyl carbons 0 1,3-diaxial 1,3-diequatorial 1,3-equatorial/axial 3.410A 5.038 A 4 569 A Cis or trans? Energy Relative energy (kcal/mol) (cis) 41.96 /moll (cis) 20.72 kJ/mol ccis) 26.68 kJ/mol Complete this sentence based on your data in the table above: The_(more/fewer)_ axial methyl groups, the (greater/lesser) the energy of the molecule.

Answer 1

1.1,3-di axial 3.410 A CH3 CH3 Diaxial position of methyl group forces them to be clsoe to each other. Steric repulsion of methyl-methyl and methyl-H increases the energy of the molecule. Hence, it is less stable. Energy: 41.96 kJ/mol (cis isomer) 2. 1,3-di equitorial 5.038 A Diequitori ally substituted methyl groups are as far apart as possible in the molecule facing away from each other. Hence, they face no steric interaction and are very stable. Energy: 20.72 kJ/mol (cis isomer) CH3 H-Ր ` 3.1.3-axial/equitorial 4.569 A Here one methyl group is axial and another is equitorial. Hence, the axial group faces di axial interaction with axial H groups. Hence, the steric repulsion is there, but it is less severe than the diaxial isomer. Hence, it is less stable than the di equitorial isomer and more stable than di axial isomer. Energy: 26.68 kJ/mol (trans isomer). HC Now, we can complete the sentences as follows: The fewer axial methyl groups, the lesser the energy of the molecule. The more axial methyl groups, the greater the energy of the molecule.