Molecular geometry of phenyl- and methyl-substituted ethylenes

Synthesis and stereochemistry of tetra-o-tolylethene and 1,1,2,2-tetra-o-tolylethane

“…Hence, we think that all the isomers can be described, at that temperature, in terms of a common idealized perpendicular skeleton. A static stereochemistry in terms of a propeller-like idealized skeleton would give rise, if all the isomers exist, to 16 Me signals, which was not observed. However, the spectrum at -40 °C (see Experimental Section) shows eight singlets and does not exclude that all the isomers adopt such a propeller-like conformation and undergo all a four-ring flip that is rapid on the NMR time scale: this situation also gives rise to eight signals (see below).…”

Electron spin resonance spectrum of tetrakis(p-methoxyphenyl)ethylene cation radical

“…A similar assumption has been used in calculations involving phenyl-substituted anthracenes7 and is somewhat justified by the calculations of Favini and Simonetta. 22 Even admitting only rotation about the Cs-Cs bonds, the strain can be eased by a small rotation of all of the anisyl groups out of the plane of the ethylene bond or by a larger displacement of the two fraws-related anisyl groups leaving the two remaining fraws-anisyl groups in the plane of the ethylene bond. Jones23 favored the second possibility in a study which compared the ultraviolet absorption spectrum of tetraphenylethylene with that of fran.s-stilbene.…”

Acid‐base equilibria of dipyridylethylenes studied by absorption and fluorescence spectrometry

“…Since a ring-nitrogen atom has electronic effects (-1 and -M) similar to those of a nitro-group, the first proton addition of DPE's should occur a t slightly lower p H than for styrylpyridines (4,8). Table I shows that this is in fact the case, a t least for the 111-derivatives (for 4-StP, pK = 5.7 (4)).…”

“…Unlike the 2 and 4 isomers, trans-3-StP displays only slight modifications in the absorption spectrum due to protonation, making the pK determination more difficult (4,8). Since the difference between the fluorescence spectrum of 3-StP and its conjugated acid ( As a matter of fact, 3-StP exhibits emission characteristics of the protonated form (see Table I) up to pH > 12, even if p K < 5.…”