Abstract
Syntheses of a series of 4,4′‐dimethoxystilbenes, substituted with methyl or ethyl groups in ortho and α‐positions, including the new compounds 2,2′,6,6′‐tetramethyl‐ ; α,2‐dimethyl‐ ; α,2′‐dimethyl‐ ; α,2,2′‐trimethyl‐ and α,α′,2‐trimethyl‐4,4′‐dimethoxystilbene, are described.
In most cases demethylation with pyridine hydrochloride gave the 4,4′‐dihydroxystilbenes in good yield.
Attempts to synthesize 2,2′,6,6′,α,α′‐hexamethyl‐4,4′‐dimethoxystilbene in reasonable amount were unsuccessful.
The infrared absorption spectra of the dimethoxystilbenes were measured. An increase in the out‐of‐plane C~α~‐H frequency was observed in the series: 4,4′‐dimethoxystilbene, 2,2′‐dimethyl‐, 2,2′‐diethyl‐, 2,2′,6,6′‐tetramethyl‐4,4′‐dimethoxystilbene. This increase, seemingly, parallels the increase in steric inhibition of molecular coplanarity, the same sequence being observed in the positions of the ultraviolet N → V absorption bands.
For the α‐substituted stilbenes, the C~α~‐H frequencies are located in the same region as the absorptions due to the substituted benzene rings and conclusions are uncertain.
The molecular refractions of the compounds, corrected for the alkyl substituents, decrease with increasing steric hindrance. For most compounds the decrements in molecular refraction are linearly related with the oscillator strengths of the N → V transition in the stilbene chromophore.