Olefinic vs aromatic way of substituent effects: The case of 3- and 4-substituted cyclohexa-1,3-dienamine derivatives

Abstract

Quantum chemical modeling was used to confront substituent effects in olefinic systems with an analogous situation in benzene. The B3LYP/6-311++G(d,p) method was applied to examine electron-donating properties of the amino group in a series of 3-(meta-like) and 4-(para-like) X-substituted cyclohexa-1,3-dienamines (X = NMe 2 , NH 2 , OH, OMe, Me, H, F, Cl, CF 3 , CN, CHO, COMe, CONH 2 , COOH, NO 2 , NO). As in the case of substituted anilines (PCCP, 2016, 18, 11711), the substituent properties were described by σ, charge of the substituent active region(X), and substituent effect stabilization energy descriptors; the amino group was characterized by structural and electronic parameters, whereas a transmitting moiety-by aromaticity index harmonic oscillator model of aromaticity. All applied substituent properties parameters were found to be mutually interrelated, with much better correlations for the para-derivatives than the meta-derivatives.Electron-donating ability of the amino group is stronger affected (circa 1.4 times) by substituent acting from position 4 in cyclohexa-1,3-dienamines than in aniline derivatives. It was also numerically confirmed that the reverse substituent effect acting to para-position is stronger (circa 1.14 times) in olefinic systems than in aromatic ones. Moreover, for 1-4 interactions, an increase of the electron-attracting power of the substituent increases π-electron delocalization in the olefinic series, whereas decreases it in the aromatic ones.

How far the substituent effects in disubstituted cyclohexa-1,3-diene derivatives differ from those in bicyclo[2.2.2]octane and benzene?

“…Important to notice that the slopes for 1-4 derivatives are as an average 1.333 and 1.193 for neutral and charged Y, respectively. Thus, one may say that the Bmixed^transmitting moiety-CHD-is more effective in charge transfer than the aromatic one (BEN), in line with earlier reports [31]. In contrast, for 1-3 interactions, the benzene moiety is more effective than CHD except for Y = NH 2 , the slopes are between 0.556 and 0.846.…”

“…Alike in the case of substituted CHD-amine derivatives [31], much better correlations are found for the 1-4 series than the 1-3 ones. The same can be stated taking into account Hammett-like relations, i.e., cSAR(Y) vs SESE, cSAR(Y) vs cSAR(X), or cSAR(Y) vs σ (Table S12).…”

“…The vibrational frequencies were calculated at the same level of theory to confirm that all obtained structures correspond to the minima on the potential energy surface. In the case of amino series, previously obtained structures [31] were used.…”

On the relations between aromaticity and substituent effect

“…Molecular systems of the series X-R-Y have been investigated for 16 substituents and seven Breaction Scheme 1 Graphical presentation of q(X) (a) and cSAR(X) (b) definitions. sites^, Y = NO 2 [116,117], OH [118], COOH [119], NH 2 [120,121] as well anionic COO − [119] and O − [118] moieties, with substituents in three and four positions of R = benzene or cyclohexa-1,3-diene. In addition, the use of both traditional and quantum chemistry-based descriptors of SE allows us to answer the question of how far the substituent effect in disubstituted cyclohexa-1,3-diene derivatives differ from those in bicyclo[2,2,2]octane and benzene [122].…”

The response of electronic and energetic properties of conjugated vs aromatic molecules to an external uniform electric field

“…The second aim was connected to the recent results of the comparison of the effect of substituents in cyclohexa-1,3-diene derivatives and in benzene [22]. It appeared that the donating ability of the NH 2 group was around 1.4 times more strongly affected by a series of substituents in the para position to the NH 2 group when the transmitting moiety was olefinic than when it was aromatic.…”