Cyano group substituent constants

A very interesting observation was the decrease in basicity of the cyano group in a-sulphur-substituted nitriles in comparison with the corresponding sulphur-free compounds75. The basicity constants for the nitriles (Table 11) were corrected to give lg Kas + SEs values. These values consider the steric effects of the substituents. 

Cyclopentadiene is such a reactive 1,3-diene that it undergoes Diels-Alder reactions with all cyano-substituted ethenes. The rate constants of these cycloadditions (Table 15.1) show that each cyano substituent increases the reaction rate significantly and that geminal cyano groups accelerate more than vicinal cyano groups. 

Since the ethylsulfonyl group (8p = 0.68) exhibits the same electron-withdrawing power as cyano group (8p = 0.66) in the Hammett substituent constant 88,105 , TESQ was expected to display a similar polymerization behavior as an acceptor monomer to TCNQ. However, it has been found that in the charge-transfer... 

An experimental kinetic study has shown that the influence of the a-cyano group on the rate of solvolysis of 2-propyl sulphonates, namely the k(HCMe20Ts)//c(NCCMe20Ts) ratio (extrapolated from 80-170 °C temperature interval to 25 °C) in 100% 2,2,2-trifluoroethanol buffered with 2,6-lutidine, is only 3.5 x 103. This is considerably smaller than the retardation factor expected on the basis of the Taft polar substituent constant. To evaluate the possibility that the investigated methacrylonitrile formation reaction proceed by a rate-limiting concerted E2 elimination, the effect of a-deuterium substitution on the rate of... 

If one takes the two different three-bond carbon-proton coupling constants in allenes into consideration only a poor correlation with overlap populations Qscsh observed. Taken separately, however, the two different three-bond CH couplings of allenes exhibit acceptable correlations with overlap populations (546). Omitting the cyano group from the regression one obtains for the couplings involving no atom which is directly linked to a substituent the correlation (134) (/ = —0.8989, Q oh in units of 10 ). 

Log P (log of the octanol/water partition coefficient) values were obtained from Basak et al. (1984), Hunter et al. (1985), and Veith et al. (1983). Taft substituent constants a ) were obtained from Dean (1985). The substituent constants were obtained from Charton (1981). For the analysis, the values of the substituent constants for the carbon atom alpha to the cyano, alcohol, or carbonyl carbon were summed. If there was more than one alpha carbon, the highest surh was used. When a sigma constant was not listed in the references, a value was estimated from values for similar structures. This was done only for alkyl groups or substituents on alkyl chains where a trend in sigma constant values versus alkyl chain length could be determined. 

Substituent effects on proton transfer to water of protonated aniline derivatives have been investigated by picosecond time-resolved fluorescence measurements [92-94]. Protonated aniline in the Sj state releases proton to water with a rate constant of 1.3 x 10 °s in aqueous solution. The proton transfer rate is significantly increased by substitution of cyano group at the meta-position k = 3.7 x 10"s ). In contrast, the methoxy substitution at the meta-position decreases the rate remarkably... 

UV-vis spectra containing a well-resolved peak at ca 530 nm with two shoulders between 380 and 590 nm. The IR v(C=C) bands are between 2031 and 2045 cm considerably lower than the bis-adducts (ca 2100 cm ), and decrease with increasing electron-accepting power of the substituents (linear correlation with Hammett constants). Changes may occur by a donor effect, d j —> r (C=C) back-donation, or r(C=C) -> d r donation. In contrast with CO and cyano complexes, where d -> 7r (CX) back-donation occurs, here the changes in y(C=C) result from electron donation from the alkynyl group to the Ru2 center. 

Table 4.6 shows the effects of a substituent on linear and branched alkanes. The effect on the a-carbon parallels the electronegativity of the substituent except for bromine and iodine.t The effect at the /3-carbon seems fairly constant for all the substituents except for the carbonyl, cyano, and nitro groups. The shift to the right at the y carbon results (as above) from steric compression of a gauche interaction. For Y = N, O, and F, there is also a shift to the right with Y in the anti conformation, attributed to hyperconjugation. 

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