Comparative studies on CH⋯F⁻hydrogen bond formation in benzene and exocyclically substituted pentafulvene derivatives

Abstract

Optimization of CH⋯F À complexes of exo-substituted pentafulvene and meta-substituted and para-substituted benzene (substituents: NMe 2 , NHMe, NH 2 , NHOH, OH, OMe, Br, Cl, F, Me, CCH, CF 3 , CONH 2 , COMe, CHO, NO 2 , NO, and CN) have been performed at the density functional theory level by using Becke hybrid B3LYP functional with 6-311++G(d,p) basis set. The acidity of the ring CH bond in benzene and fulvene are of similar magnitude, whereas the acidity of the fulvene exocyclic CH 2 group is significantly higher. Various properties based on the H⋯F À hydrogen bond (bond length, electron density at BCP, and bond dissociation energy), and the whole molecule (HOMA, sEDA, pEDA, substituent active region, and substituent effect stabilization energy) were analyzed and compared between the fulvene and benzene systems. Sensitivity of the ring CH⋯F À hydrogen bond and other substituent dependent properties to substituent effect is substantially greater in fulvene than that of benzene derivatives. In fulvene, the 3-position is more sensitive than the 4-position. The sEDA and pEDA parameters used to measure sigma-electron and pi-electron excess/deficiency of the ring are mutually correlated for the studied systems.

On the nonadditivity of the substituent effect in homo-disubstituted pyridines

“…The plots of sEDA and pEDA descriptors constructed for monosubstituted benzenes, triazoles, and methanes revealed that they are well transmissible between the different monosubstituted molecular systems. [1] For the monosubstituted pyridines (Scheme 1), this is also the case. For systems substituted by the -BF 2 , -BH 2 , -Br, -CHO, -Cl, -CN, -COOH, -F, -Li, -N(CH 3 ) 2 , -NH 2 , -OCH 3 , -OH, -SH, and -tBu, groups, for which the sEDA and pEDA substituent effect descriptors cover a sufficiently large range (see Supporting Information), the regression coefficients of the linear correlations between the sEDA descriptors for the 2-, 3-, and 4-substituted pyridines and monosubstituted benzenes are equal to 0.999 ( Figure 1A).…”

“…The perfect linearity of correlation between the sEDA descriptors constructed for benzenes and pyridines confirms our previous findings that the effect on σ-electron system of the substituted ring expresses the substituent group electronegativity and is limited to the closest surrounding of the ipso C-atom. [1,[5][6][7] In fact for 2-substituted pyridines, in which a substituent is in ortho-position to the N-atom (which can be treated as σ-electron withdrawing incorporant of a parent benzene system [5] ), both a substituent and the N-incorporant [5] act together, yet in an additive way ( Figure 1A). On the other hand, if the 2-, 3-, and 4-substituted pyridines were treated as benzene incorporated with the N-atom [5] and additionally substituted in ortho-, meta-, and para-positions, respectively, then the substantial nonlinearity of the correlation between pEDA descriptors appears for the ortho-and para-substitutions, while for the meta-substituted pyridines, it is less noticeable.…”

“…Seven years ago, Ozimiński and Dobrowolski have introduced the sEDA and pEDA descriptors of the substituent effect evaluating the electron shift between a substituent and separated σand π-electron systems of the core molecule. [1] They are expressed in terms of the number of electrons donated to or withdrawn from the core molecule by a substituent. Thus, in classical terms used in substituent effect studies, the sEDA descriptor spells the substituent group electronegativity whereas the pEDA descriptor rates the resonance factor.…”

“…[2][3][4] The sEDA and pEDA descriptors were next modified to evaluate heteroatom or heteroatomic group incorporation effect into a cyclic systems (sEDA(II) and pEDA (II)), [5] to estimate substituent effect caused by a doublebonded substituent (sEDA(=) and pEDA(=)), [6] and to determine the heteroatom incorporation effect into a ring junction position (sEDA(III) and pEDA(III)). [7] The sEDA and pEDA descriptors of the classical substituent effect, now often referred by us as sEDA(I) and pEDA(I), were used to study a variety of problems: aromaticity of different systems, [7][8][9][10][11][12][13][14][15][16][17][18][19] stability and tautomerism, [20][21][22] vibrational and nuclear magnetic resonance spectra, [23][24][25] optical molecular switches, [26][27][28][29] halogen bond problems, [30] reaction course analysis, [31] and general issues connected to the substituent effect. [32][33][34] One of the general problems of the substituent effect is its nonadditivity.…”

“…The sEDA(I) and pEDA(I) descriptors for monosubstituted pyridine were constructed after the work of Ozimiński and Dobrowolski [1] using the following equations:…”