Cyano position shift

A number of cis/trans 4,6-dialkyl-2,2-dimethyl-l,3-dioxanes were studied by C NMR spectroscopy (93JOC5251). The C NMR shifts of C -Me groups (Scheme 8) were found to be very sensitive to the 1,3-dioxane conformation [chair form Me(ax) ca. 19 ppm and Me(eq) ca. 30 ppm— pure 30.89 ppm in the twist-boat form both methyl carbons resonate at ca. 25 ppm (pure 24.70 ppm)]. With these values, AG° of the chair to twist-boat equilibrium was calculated (Table IV). For 13a (nitrile), 13b (alkyne), and 13e (methyl ester) (Scheme 8) in CH2CI2, the temperature dependence of the AG° values was determined. Depending on the substituent, small negative or positive entropy terms were found generally the enthalpy term dominates the -AG° value. In the tram isomers 13, the cyano and alkyne substituents favor the chair conformation, but CHO, ester, alkene, and alkyl substituents, respectively, clearly favor the twist-boat conforma-... 

Heteroaromatic naphthalene derivatives generally have a lower HOMO-LUMO gap than the analogous phenylene-based compounds, leading to a bathochromic shift of the PL emission maxima. By superimposing the PL spectra of 364 (X = 469 nm/498 nm) and the corresponding triflone 365 (X = 485 nm), it can be shown that replacement of cyano by triflyl does not shift the spectral position of the nathylenevinylenes. 

Both absorption and emission maxima of the polymer 592 with cyano groups in the (3-position with respect to the thiophene nucleus are hypso-chromically shifted as compared to the polymer 593 (having the cyano group in the a-position), which can be explained by steric interactions between the cyano and alkoxy groups. Nevertheless, both copolymers 592 and 593 exhibit pure red-light emission with chromaticity values very close to standard red. 

The significant influence of R1 and R2 on color is quite surprising because these substituents are not components of the chromophore system. Ester and, especially, cyano groups in these positions cause a distinct hypsochromic shift [9],... 

Electronic spectral shifts induced in the model fragment 75 by the introduction of a dimethylamino or cyano group into different positions were computed by MO-LCAO methods. ... 

The effects of various non-tautomeric amino substitutents and of cyano group on the position of the tautomeric equilibrium were studied by UV, IR, and mass spectroscopy (78KG793). Although all the studied compounds 3-6 exist predominantly in the oxo form in polar solvents and in hydroxy form in non-polar solvents, the presence of the 3-cyano group or inclusion of the amino substituent into the ann-elated ring leads to the shift in the equilibrium favoring the hydroxy form. 

The effect of substituents on the vinylene unit depends upon their steric bulk, so that the cyano groups in CN-PPV (22) seem to have no effect upon the position of the emission maxima, whereas the bulky aryl substituents in 40 or 42 produce a marked blue-shift. 

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