Molecular motion in solid bicyclo[2.2.2]octane and bicyclo[2.2.2]oct-2-ene studied by nuclear magnetic resonance

McGuigan, S.; Strange, John H.; Chezeau, J.M.; Nasr, M.

doi:10.1051/jphys:01985004602027100

Cited by 9 publications

(2 citation statements)

References 29 publications

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“…An average E a value of 1.15 kcal/mol deduced in this manner is smaller than those of the methyl and methoxy groups in the same structure, suggesting that small jumps in a six-fold potential are advantageous when compared to the larger 120° jumps required for rotation of the smaller methyl groups. The barrier in crystals of 3 is also smaller than the one reported for the reorientation of pure BCO over its 1,4 axis in its plastic crystalline state (1.84 kcal mol −1 ), 29 and the structurally related and also positionally disordered one in 1,4-bis(iodoethynyl)bicyclo[2.2.2]octane (1.48 kcal mol −1 ). 15 …”

Section: Resultsmentioning

confidence: 62%

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

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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. Using 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 = 1.91 kcal mol−1), despite their smaller moments of inertia and surface areas.

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Section: Resultsmentioning

confidence: 62%

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

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“…0.8 GHz. Comparatively, in the high-temperature plastic crystalline phase I, pure bicyclo[2.2.2]octane has an activation energy of 1.84 kcal·mol −1 for rotation about the 1,4 axis . This is 24% larger than E a = 1.48 kcal·mol −1 for the same rotational motion about the 1,4-axis of bicyclo[2.2.2]octane in the faster BIBCO rotor.…”

Section: Resultsmentioning

confidence: 99%

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

et al. 2011

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As a point of entry to investigate the potential of halogen-bonding interactions in the construction of functional materials and crystalline molecular machines, samples of 1,4-bis(iodoethynyl)bicyclo[2.2.2]octane (BIBCO) were synthesized and crystallized. Knowing that halogen-bonding interactions are common between electron-rich acetylenic carbons and electron-deficient iodines, it was expected that the BIBCO rotors would be an ideal platform to investigate the formation of a crystalline array of molecular rotors. Variable temperature single crystal X-ray crystallography established the presence of a halogen-bonded network, characterized by lamellarly ordered layers of crystallographically unique BIBCO rotors, which undergo a reversible monoclinic-to-triclinic phase transition at 110 K. In order to elucidate the rotational frequencies and the activation parameters of the BIBCO molecular rotors, variable-temperature (1)H wide-line and (13)C cross-polarization/magic-angle spinning solid-state NMR experiments were performed at temperatures between 27 and 290 K. Analysis of the (1)H spin-lattice relaxation and second moment as a function of temperature revealed two dynamic processes simultaneously present over the entire temperature range studied, with temperature-dependent rotational rates of k(rot) = 5.21 × 10(10) s(-1)·exp(-1.48 kcal·mol(-1)/RT) and k(rot) = 8.00 × 10(10) s(-1)·exp(-2.75 kcal·mol(-1)/RT). Impressively, these correspond to room temperature rotational rates of 4.3 and 0.8 GHz, respectively. Notably, the high-temperature plastic crystalline phase I of bicyclo[2.2.2]octane has a reported activation energy of 1.84 kcal·mol(-1) for rotation about the 1,4 axis, which is 24% larger than E(a) = 1.48 kcal·mol(-1) for the same rotational motion of the fastest BIBCO rotor; yet, the BIBCO rotor has three fewer degrees of translational freedom and two fewer degrees of rotational freedom! Even more so, these rates represent some of the fastest engineered molecular machines, to date. The results of this study highlight the potential of halogen bonding as a valuable construction tool for the design and the synthesis of amphidynamic artificial molecular machines and suggest the potential of modulating properties that depend on the dielectric behavior of crystalline media.

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Vibrational spectroscopic study of the three solid phases of bicyclo[2.2.2]octene

Kawai

Butler

Gilson

1992

J Raman Spectroscopy

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The three solid phases of bicyclo[2.2.2]oct-2-ene were characterized by vibrational spectroscopy at low tern peratures and high pressures. Bicycloocteae undergoes a phase transition at 176 K on cooling (phase I -B phase 11) and then another at ca 95 K (phase II + phase 111). On compression at room temperature, these same tramitions occur at 7.9 f 1.0 kbar and cu. 15 kbar. The low-frequency Raman spectra show that phase I is isotropically disordered, whereas phase 11 is anisotropically disordered. The crystal structure of phase I1 is, however, similar to that of phase 111, and is suggested to be tetragonal.

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Molecular motion in solid bicyclo[2.2.2]octane and bicyclo[2.2.2]oct-2-ene studied by nuclear magnetic resonance

Cited by 9 publications

References 29 publications

Amphidynamic Crystals of a Steroidal Bicyclo[2.2.2]octane Rotor: A High Symmetry Group That Rotates Faster than Smaller Methyl and Methoxy Groups

Amphidynamic Crystals of a Steroidal Bicyclo[2.2.2]octane Rotor: A High Symmetry Group That Rotates Faster than Smaller Methyl and Methoxy Groups

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

Vibrational spectroscopic study of the three solid phases of bicyclo[2.2.2]octene

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