Conformers, Energetics, and Basicity of 2,2‘-Bipyridine

Abstract

The proton affinities of the cis and trans conformers of 2,2′-bipyridine have been determined at the MP2/ 6-31G**//HF/6-31G** level of theory. The neutral molecule and its protonated cation are both shown to possess stable cis and trans conformers: the barriers for cis/trans interconversion, and the roles that electrostatic interactions and π-conjugation play in these barriers, are analyzed. In addition, the barriers to rotation through planar structures are reported. The structures, the effect of electron correlation on the energetics, and the ground state charge distributions are discussed (i) with respect to biphenyl and 2,2′-bipyrimidine and (ii) in the context of dinitrogen proton sponges. With regard to (i) and cis f trans interconversion, it appears that biphenyl, 2,2′-bipyridine, and 2,2′-bipyrimidine have almost identical conformers and rotational energetics. With regard to (ii), these results indicate that SCF estimates of proton affinities and proton transfer barriers in such compounds are overestimated (by 1-2% and ∼100%, respectively), and that barriers to rotation are underestimated by some 20-30%.

Physical Nature of Interactions in ZnIIComplexes with 2,2′-Bipyridyl: Quantum Theory of Atoms in Molecules (QTAIM), Interacting Quantum Atoms (IQA), Noncovalent Interactions (NCI), and Extended Transition State Coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) Comparative Studies

“…[2][3][4] Knowledge of the conformational structure of -diimine ligands and information about the rotational energy barrier are important and useful for a better understanding of the complex formation process and trends in stability of complexes. Hence not surprisingly, these ligands have also been extensively studied computationally [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and for over 40 years it is known that the most stable conformer of 2,2-bipyridyl has two N-atoms trans to each other (s-trans conformer). [9][10][11][12][13][14][15] Lower stability of the conformer with nitrogens cis to each other (s-cis conformer) was attributed mainly to the steric hindrance of the 3,3-hydrogen atoms and destabilizing nitrogen lone pair-lone pair interactions [11][12][13][14][15][16][17] in 2,2-bipyridyl.…”

Helicity Coding: Programmed Molecular Self-Organization of Achiral Nonbiological Strands into Multiturn Helical Superstructures: Synthesis and Characterization of Alternating Pyridine-Pyrimidine Oligomers

“…Since the residual helical moieties in the X species are directed toward the outside, this mechanism would be applicable not only for 6 but also for longer strands 1 and 3. A perpendicularly twisted 2,2'-bipyridine has been calculated to be about 29 kJ mol À1 higher in energy than its planar transoid form, [12] so that an activation free energy of about 58 kJ mol À1 would be expected for the interconversion process, assuming that a py ± pym unit presents a similar energy difference between its perpendicular and planar transoid conformations. This value is in good agreement with the experimentally observed barriers for 6 (51.6 kJ mol ).…”

Protonation Thermochemistry of Gaseous 2,2'-, 4,4'- and 2,4'-Bipyridines and 1,10-phenanthroline

“…These observations suggest that the gas phase basicity of 1 is situated between 927 and 940 kJ/mol and consequently that PA(1) is situated between 959 and 972 kJ/mol (assuming that the entropy terms is limited to the translational entropy of the proton). Tentative of theoretical estimate of PA (1) were conducted at the MP2/6-31G(d,p)// HF/6-31G(d,p) 21 and MP2/6-31G(d,p)//MP2/6-31G(d,p) 17 levels of theory. The values, 970 21 and 977 17 kJ/mol are reasonably comparable and point to the upper limit of the experimental bracketing window.…”

“…Tentative of theoretical estimate of PA (1) were conducted at the MP2/6-31G(d,p)// HF/6-31G(d,p) 21 and MP2/6-31G(d,p)//MP2/6-31G(d,p) 17 levels of theory. The values, 970 21 and 977 17 kJ/mol are reasonably comparable and point to the upper limit of the experimental bracketing window. Results obtained using the semiempirical AM1 method have been also reported, 11 they are however significantly at variance from the above recalled results since a PA(1) value of ≈ 930 kJ/mol was obtained.…”

“…Finally, molecule 1 offers a clear example illustrating the role of rotational isomerism upon thermochemical stability and basicity properties. 15,17,21,22 The goal of the present study was to use state of the art quantum chemistry methods to provide accurate heats of formation and thermochemical parameters associated with the gas phase protonation of molecules 1−4. For this purpose, the most recent composites methods G3MP2B3, G3B3, G4MP2 and G4 were used.…”