Amphidynamic Crystals of a Steroidal Bicyclo[2.2.2]octane Rotor: A High Symmetry Group That Rotates Faster than Smaller Methyl and Methoxy Groups
2013
Rodríguez-Molina, Braulio | Pérez-Estrada, Salvador | Garcia-Garibay, Miguel A.
The synthesis, crystallization, single crystal X-ray structure, and solid state dynamics of molecular rotor 3 provided with a high symmetry order and relatively cylindrical bicyclo[2.2.2]octane (BCO) rotator linked to mestranol fragments were investigated in this work. By use of solid state ¹³C NMR, three rotating fragments were identified within the molecule: the BCO, the C19 methoxy and the C18 methyl groups. To determine the dynamics of the BCO group in crystals of 3 by variable temperature ¹H spin–lattice relaxation (VT ¹H T₁), we determined the ¹H T₁ contributions from the methoxy group C19 by carrying out measurements with the methoxy-deuterated isotopologue rotor 3-d₆. The contributions from the quaternary methyl group C18 were estimated by considering the differences between the VT ¹H T₁ of mestranol 8 and methoxy-deuterated mestranol 8-d₃. From these studies it was determined that the BCO rotator in 3 has an activation energy of only 1.15 kcal mol–¹, with a barrier for site exchange that is smaller than those of methyl (Eₐ = 1.35 kcal mol–¹) and methoxy groups (Eₐ = 1.92 kcal mol–¹), despite their smaller moments of inertia and surface areas.
Show more [+] Less [-]AGROVOC Keywords
Bibliographic information
This bibliographic record has been provided by National Agricultural Library