In addition, the increase of dielectric constant from PAZ-ET to PAZ-TZ would be due to the fact that the electron-withdrawing group on the azobenzene of PAZ-TZ is the strongest.
The azo polymers with strong push-pull azo chromophores are named as PAZ-X, where X is the abbreviations to make the distinction for the different electron-withdrawing groups.
On the basis of this molecule, a series of molecules were designed by inserting different electron-withdrawing groups
(EWGs (-C[F.sub.3] (A), -CN (B), and -F (C))) into number 1, 2, 3, and 4 positions of the original molecule acceptor, respectively.
In this work, we have shown by NBO and NPA analyses that, although Cl, an electron-withdrawing group
, decreases the electron density on phenol by negative inductive effect, it also delocalizes nonbonding electrons onto the phenyl ring by resonance, thereby increasing its electron density.
The introduction of the electron- donation or electron-withdrawing group
in juglone provokes an enhancement of the interaction strength of this hydrogen bond.
This effect is apparently pronounced further for the electron-withdrawing groups rather than the electron-donating groups.
Second, electron-donating substituents increase the nucleophilicities of carboxylic acids in the glutaric acid, whereas electron-withdrawing groups decrease the nucleophilicities of carboxylic acids.
This result confirms that the dienophile containing an electron-donating group is not conducive to the DA reaction, and while the [E.sub.a], [E.sub.i], and [n.sub.Mayer] values of BD + MA are the smallest, they seem to be affected by the presence of an electron-withdrawing group, which is relatively favourable for the reaction.
The electron-withdrawing group monotonically decreases the RDG value of [C.sub.4]-[C.sub.5], while the electron-donating group produces the opposite effect.
This validated our hypothesis that the influence of the electron-donating group on increasing the RDG value of [C.sub.4]-[C.sub.5] is greater than that of the electron-withdrawing group. In brief, if the dienophile is substituted by an electron-withdrawing group, the spike value of a distal end determined by [omega] B97X-D increases slowly, while value determined by B3LYP shows a reverse trend from the RC to the IP until reaching the SP.
Upon substitution of TO with electron-withdrawing groups
, there is an increase in [omega] index, thus reflecting a higher electrophilic character.
The double bends of the Michael accepter are activated by two adjacent electron-withdrawing groups
. Alternatively or additionally, the Michael donor contains beta-ketoamide, enamine carboxylate, enamine amide, pyrazolone, isoxazolone, hydantoin, rhodanine, thio-substituted unsaturated ester, thio-substituted lactone or phosphonite or phosphinite ester groups.