Molecules Methyl Research Articles

Excitations of safranin and phenosafranin in aqueous solution: Comparative theoretical analysis

In the present work, the excitations of safranin (SAF) and phenosafranin (PheSAF) in an aqueous solution are analyzed by DFT/TD-DFT, considering the vibronic transitions and hydration. The frontier orbitals, transitions between which cause the absorption and emission of dyes in the visible region of the spectrum, almost do not cover benzene rings and methyl groups of molecules. As a consequence, benzene rings, aromatic hydrogen atoms, as well as SAF methyl groups are not covered by the change in electron density. These features explain the same excitation energies of SAF and PheSAF observed experimentally. At the same time, during relaxation to an excited equilibrium state, the changes in the vast majority of atomic charges again turn out to be different for SAF and PheSAF, which causes a slight difference between the emission energies of dyes. Excitations of both dyes do not lead to twisting of their benzene rings relative to the chromophores - the dihedrals between them are strictly φ = 90°. The thermal twisting of these dihedrals is practically free up to Δφ∼±30°, and then it is sharply hampered. The heights of potential barriers separating their energy minima are very high (∼400 kT). The increase in the dipole moments upon excitation is due to the greatest extent to the significant increase in the electron densities at the N10 atoms of both dyes. All five H-bonds of each of the dyes with water are strengthened upon excitation. The strongest and most enhanced due to excitation are the H-bonds of waters with the N10 atoms. There is a strong photoinduced polarization of water molecules bound to the N10 atoms of the dyes. H-bonds with water of amino groups are stronger in PheSAF, and with the N10 atom, in SAF. The influence of hydrating water molecules leads to significant bathochromic shifts of the maxima of the calculated spectra (23 nm for SAF and 22 nm for PheSAF) relative to the purely implicit specification of the solvent.

(2Z)-2-Fluoro-N-{4-[5-(4-fluorophenyl)-2-methylsulfanyl-1H-imidazol-4-yl]-2-pyridyl}-3-phenylacrylamide

The asymmetric unit of the title compound, C24H18F2N4OS, contains two crystallographically independent mol­ecules, A and B, which are linked into two chains of A and B mol­ecules by inter­molecular N—H⋯O hydrogen bonds. The three-dimensional network is stabilized by π–π inter­actions between the pyridine rings and phenyl rings of different residues, with centroid–centroid distances of 3.793 (1) and 3.666 (2) Å. The mol­ecular conformation is stabilized by intra­molecular N—H⋯F hydrogen bonds (2.15/2.15Å). The imidazole rings make dihedral angles of 39.5 (2)/38.5 (2) and 31.8 (2)/33.2 (2)° with the 4-fluoro­phenyl rings and the pyridine rings, respectively. The methyl group of molecule A is disorderd in a 0.60:0.40 ratio.

2-(1H-Benzoimidazol-2-yl)-6-ethoxyphenol

The title Schiff base compound, C15H14N2O2, consists of two crystallographically independent mol­ecules, A and B. Mol­ecule A is almost planar, whereas mol­ecule B is slightly twisted, the dihedral angles between the benzimidazole group and the benzene rings being 2.65 (12) and 13.17 (15)°, respectively. The methyl group of mol­ecule B is disordered over two positions, with a refined site-occupancy ratio of 0.581 (7):0.419 (7). In each mol­ecule, intra­molecular O—H⋯N hydrogen bonds generate S(6) ring motifs. In the crystal structure, both types of mol­ecules are linked via inter­molecular bifurcated N—H⋯O hydrogen bonds into one-dimensional extended chains along [010] and form R 1 2(5) ring motifs. The crystal structure is further stabilized by inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distances = 3.4758 (16)–3.596 (2) Å].

Palladium‐Mediated C—H Activation in the Field of Terpenoids: Synthesis of Rostratone.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium mediated C–H activation in the field of terpenoids: synthesis of rostratone

We present results, which indicate that Pd-mediated C–H bond activation can be used under mild conditions for the remote functionalization of C-4 methyl groups of molecules with different terpenoid-like skeletons containing six- or seven-membered A rings. This procedure has allowed us to complete a novel strategy for the synthesis of γ-dioxygenated terpenoids in three stages: (i) selective epoxidation of commercial polyenes, (ii) titanium(III)-catalyzed cyclization of epoxypolyprenes, and (iii) Pd-mediated remote functionalization of equatorial methyl groups. This strategy has proved to be useful for the synthesis of the natural labdane rostratone (1).

Microwave spectrum, structure, and barrier to internal rotation of acetone

The microwave spectrum of (CH 3) 2CO has been reinvestigated and the spectra of two additional isotopic species, ( 13CH 3) 2CO and (CH 3) 3C 18O, have been observed and assigned. These data together with data previously reported for (CD 3) 2CO are used to calculate a structure based on the assumption of a symmetrical methyl group. The r s structural parameters obtained are: CC = 1.507 Å CCC = 117° 12′ CO = 1.222 Å HCH = 108° 46′ CH = 1.085 Å 2θ = 119° 54′ where 2θ is the angle between the symmetry axes of the methyl groups as determined by analyses of multiplet splittings arising from coupling of internal and over-all rotation. These same analyses yield barriers to internal rotation of 778, 777, and 726 cal/mole for the species (CH 3) 2CO, ( 13CH 3) 2CO, and (CD 3) 2CO, respectively. Evidence for the general occurrence of “tilted” or “cocked” methyl groups in molecules with methyl groups attached to doubly bonded carbon atoms is presented and discussed.