Rotation barrier intramolecular

Rotational barriers and intramolecular S - - - O interactions were studied for acyliminothiadiazolines at the Hartree-Fock level [98JA3104]. 

H3SiOCSN(CH3)2 the free rotation barrier differs only slightly from that of H3SiOCON(CH3)2 and no magnetic equivalence is observed even at +60 °C. Therefore, an intramolecular interaction between the silicon atom and the carbonyl oxygen in the first compound has been su estai The fact that no broadened signals... 

Chandross and Depster (16) studied the temperature dependence of the rate constant of excimer formation for l,3-bls(a-naphtyl) propane and for l,3-bls(3-naphtyl)-propane. They found an activation energy of 4 kcal/mol, comparable to the energies related to the rotation barrier in a methylene chain. Recently Avourls, Kordas, and El-Bayouml studied the time dependence of the intramolecular excimer fluorescence of 1,3-dlnaphtylpropane. They determined rate constants kg and k j at different viscosities (37). 

Buemi, G., and Zuccarello, F., Is the intramolecular hydrogen bond energy valuable from rotation barriers J. Mol Struct. Theochem, 581, 71-85 (2002). 

Shchavlev, A.E., Pankratov, A.N., and Shalabay, A.V., DFT computational studies on rotation barriers, tautomerism, intramolecular hydrogen bond and solvent effects in 8-hydroxyquinoline, Int. J. Quantum Chem., 106, 876-886 (2006). 

Kwon, Y., Theoretical studies on o-aminofuranaldehyde and o-aminofuranthioaldehyde in reaction field C-C rotational barriers and intramolecular hydrogen bonding, J. Mol. Struct. Theochem, 496, 217-226 (2000). 

Remko, M. 1983. MO investigations on lignin model compounds. XV. Effect of intermolecular hydrogen bond on rotational barrier of the intramolecular hydrogen bonded guaiacol hydroxyl group. Z. Phys. Chem. (Wiesbaden), 134 129-134. 

As this chapter is concerned with the intramolecular variants of iminium ion initiated condensations, a brief outline of possible cyclization modes is in order (Scheme 1). Examples (a) and (b) depict the generation of monocyclic compounds by way of exocyclic-trigonal and endocyclic-trigonal cyclizations, respectively. Cases (c), (d) and (e) exemplify the construction of bicyclic compounds. Since rotational barriers for simple iminium ions are comparable to those of alkenes, all of these cyclization modes... 

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