8-Oxoguanine is a mutagenic oxidative damage product of guanine that has been the subject of many experimental studies. Despite numerous references to this damaged base, its precise configuration or population of configurations in equilibrium are unknown, as it can be drawn in over 100 potential neutral and ionized tautomeric forms. The structural uncertainty surrounding 8-oxoguanine complicate...

In the title compound, C19H15N3O3, which crystallizes as the phenol-imine tautomer, the dihedral angle between the aromatic rings bridged by the NH unit is 47.16 (16)°. The dihedral angle between the rings bridged by the imine unit is 6.24 (15)°; this near coplanarity is reinforced by an intra-molecular O-H⋯N hydrogen bond, which generates an S(6) ring. In the crystal, N-H⋯O hydrogen bonds gene...

The title Schiff base, C(17)H(14)N(2)O(3), exists as an NH tautomer with the H atom of the phenol group transferred to the imine N atom. The iminium H atom is involved in a strong intra-molecular N(+)-H⋯O(-) hydrogen bond to the phenolate O atom, forming an S(6) motif. In the crystal structure, N-H⋯O hydrogen bonds form a C(9) chain parallel to [100] and a C(11) chain parallel to [010], while C...

A detailed investigation of a valence tautomeric (VT) transition for the new complex [Co(III)(3,5-DBCat)(3,5-DBSQ)(py)₂]/[Co(II)(3,5-DBSQ)₂(py)₂] (1) is reported, where 3,5-DBCatH₂ is 3,5-di-tert-butyl-catechol, 3,5-DBSQH is 3,5-di-tert-butyl-semiquinone and py is pyridine. Complex 1 exists as a mixture of the two valence tautomers, with the relative proportion of each depending on the external...

High-level ab initio electronic structure calculations, including extrapolations to the complete basis set (CBS) limit, were performed, and highly precise relative energies of five-member N-heterocycles were determined. Nitrogen-containing heterocycles studied included tautomers of tetrazole (CH(2)N(4)) and triazoles (C(2)H(3)N(3)). Valence focal-point analysis of 1H-tetrazole, 2H-tetrazole, 5H...

In the mol-ecule of the title compound, C(16)H(17)NO(3), the aromatic rings are oriented at a dihedral angle of 29.25 (8)°. An intra-molecular O-H⋯N hydrogen bond results in the formation of a nearly planar [maximum deviation 0.034 (13) Å] six-membered ring, which is oriented at dihedral angles of 0.91 (1) and 28.91 (12)° with respect to the aromatic rings. The title mol-ecule is a phenol-imine...

Combined density functional and multireference configuration interaction methods have been employed to explore the ground and low-lying electronically excited states of the most important tautomeric and rotameric forms of guanine with the purpose of resolving the conflicting assignments of IR-UV bands found in the literature. The calculations predict sharp 1(pi-->pi*) origin transitions for the...

A series of 2-pyridyl-pyrazole derivatives 1-4 possessing five-membered ring hydrogen bonding configuration are synthesized, the structural flexibility of which is strategically tuned to be in the order of 1 > 2 > 3 > 4. This system then serves as an ideal chemical model to investigate the correlation between excited-state intramolecular proton transfer (ESIPT) reaction and molecular skeleton m...

The enol tautomers of the aromatic oc-keto acids combine instantaneously and reversibly with borate to form complexes of a mixed ester-anhydride structure, thereby displacing the apparent keto-enol equilibrium in favor of the enol tautomer. The enol tautomer and its borate complex have strong absorption in the 300 ml* region (1). This strong absorption is the basis of the spectrophotometric met...

Automated registration of compounds from external sources is necessitated by the numerous compound acquisitions from vendors and by the increasing number of collaborations with external partners. A prerequisite for automating compound registration is a robust module for determining the structural novelty of the input structures. Any such tool needs to be able to take uncertainty about stereoche...