Unconventional O–H···C Hydrogen Bonding and Effects of Conformational Changes on Infrared Spectroscopy of <i>o</i>‑Cresol in Solutions

The unconventional O–H···C intramolecular hydrogen bonding and the effect of conformational changes on IR spectra of <i>o</i>-cresol in aqueous solutions were investigated by using molecular dynamics (MD) simulations, density functional theory (DFT), and experiments. A facial rotational isomerization between global minimum with <i>trans</i> conformation and the <i>cis</i> isomer is predicted to take place in gas phase with a low barrier of about 3.7 kcal/mol through a <i>vertical</i>-like transition state. Upon solvation in aqueous solution, the contents of energetically high–lying <i>vertical</i> and <i>cis</i> conformations of neutral <i>o</i>-cresol are increased to 19% and 57%, respectively, in comparison with those (<i>vertical</i>, 0%; <i>cis</i>, 27%) in vacuum. The IR spectra of aqueous solution are closely related to the relative population of the different conformations, especially for the <i>cis</i> conformation with hydroxyl group facing to alkyl group. The appearance of <i>cis</i> conformations and unconventional O–H···C intramolecular hydrogen bond (HB) caused the low-frequency shift in OH stretching vibration of the IR spectra, which was also correlated with cation-like charge distribution and the decrease in <i>s</i>-component of oxygen hybridization orbital. However, the intermolecular HB between the <i>o</i>-cresol and surrounding water (<i>o</i>-cresol) molecules gave rise to more evident shifts in IR spectra than that caused by the intramolecular HB contributions in <i>cis</i> isomer. Further identification of intramolecular HB effect is performed through the comparison of spectrum changes that occurs on passing from aqueous solution to less interacting (carbon tetrachloride and cyclohexane) solvents. The absence of the intermolecular HB interaction between <i>o</i>-cresol and carbon tetrachloride (and cyclohexane) solvents leads to the weaker intensity and narrower width of OH stretching vibration region (around 3407 cm^–1) in the IR spectra than that in aqueous solution

Visible-Light-Promoted Radical C–H Trifluoromethylation of Free Anilines

The trifluoromethyl-substituted anilines are biologically active compounds and useful building blocks. In this communication, we have developed the first visible-light-induced radical tri­fluoro­methyla­tion of free anilines with the commercially available and easily handled Togni reagent at room temperature. The resulting products were successfully transformed into a variety of valuable fluorine-containing molecules and heterocyclic compounds. This protocol provides an economical and powerful route to trifluoromethylated free anilines

Role of Planar Conformations in Aggregation Induced Spectral Shifts of Supermolecular Oligofluorenols in Solutions and Films: A Combined Experimental and MD/TD-DFT Study

The supramolecular approach of fluorenol polymers brings about excellent self-assembly behavior to fabricate organogels and superstructured thin films through highly directional noncovalent interactions. To understand the aggregation effects on electronic structures, the packing structures and the UV/vis absorption spectra of oligofluorenols (PFOH<i>n</i>, <i>n</i> = 1/3–8), with and without OC₈H₁₇ side chains, were studied experimentally and theoretically in crystal, amorphous solids, and solutions, respectively. For the ground state in vacuum the steric repulsion between two adjacent fluorenol units renders the PFOH oligomers twisted in a helix conformation, while the molecular aggregation favors the appearance of planar π-conjugated structures. In comparison with the crystal packing, the content of planar conformation (with the torsion angle less than 20°) is increased in amorphous solids. The hydroxyl groups in oligofluorenols facilitate the formation of hydrogen bonding networks. The red shift in absorption spectra was observed in a systematic experimental study of unsubstituted and substituted oligofluorenols with the increasing concentration both in toluene and chloroform solutions. The subsitituted oligofluorenol R-PFOH1 with only one OC₈H₁₇ side chain exhibited a shoulder peak at 430–440 nm, which is different from PFOH1 without side chain and 3R-PFO1 with three OC₈H₁₇ side chain. Time-dependent density functional theory (TDDFT) calculations, which were carried out on conformation ensembles taken from a series of molecular dynamics (MD) simulations, revealed that the increase in the content of planar π-conjugated conformations is correlated to the red shift in the absorption spectra upon increasing the solution concentrations. The aggregation-induced red-shift in absorption spectra of oligofluorenols, as well as the blue-shift for oligothiophenes, was rationalized in a unified way from the increased (and reduced) content of planar conformations in molecular aggregates