Computational Study of Substituent Effects on Gas
23rd IUPAC Conference on Physical Organic Chemistry (ICPOC23) 3rd – 8th July 2016 • Sydney • Australia
Computational Study of Substituent Effects on Gas-Phase Stabilities of Phenylboranylmethyl Anions K. Nakata,a,* and M. Fujiob a
b
Science Research Center, Hosei University, Tokyo, Japan Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, Japan *[email protected]
Stabilities of anions of aromatic compounds are governed by three kinds of electronic effects, and an extended Yukawa-Tsuno equation (1) was recently proposed to describe the substituent effects.1 −ΔE X = ρ (σ 0 + r − Δσ R− + sΔσ S )
(1)
0
The normal substituent constant (σ ) measures the basic electron-donating or -withdrawing ability for all ring substituents. The resonance ( Δσ R– ) and saturation ( Δσ s ) substituent constants measure the ability of through-resonance and saturation effects, respectively. Resultant r– and s values reveal the degree of through-resonance and saturation effects in a given system, respectively. To confirm the validity of Eq. (1) and reveal the physical meanings of the r– and s values, we report here the substituent effects on gas-phase stabilities of phenylboranylmethyl anions (1). Relative stabilities of ring-substituted 1 were determined as energy differences (ΔEX) of the reactions (2). φ
H C H + B X H
H +
H
X
φ 1
H C H B H
(2)
−ΔEx / kcal mol-1
The energies of respective species included in the reactions were calculated at the B3LYP/6-311 +G(2d,p) level of theory. Obtained substituent p-NO2 H H effects were accurately analyzed by Eq. (1) to H H C C p-NO B H B H give the r–=0.59. (Fig. 1) A significant 15 p-CN delocalization of the negative charge to the m-NO2 p-CHO X 1 X benzene π-electron system was observed in 1, m-CN 10 p-COMe although such the canonical form cannot be p-CF3 m-CHO m-CF3 drawn. A NBO analysis explained the throughρ = 16.59 m-COMe m-Cl r - = 0.59 resonance via the orbital interaction between the 5 m-F s = 0.65 p-Cl π-orbital of side chain and the π*-orbital of p-MeO-m-Cl R = 0.999 benzene. Substituent-effect analyses were further SD = 0.32 H m-MeO p-t-Bu performed for 1 of which the dihedral angle φ 0 m-Me :σ p-Me p-MeO : σ− between the benzene and side chain planes was p,m-Me2 m-Me2N – : σ0 p-Me2N fixed. While the s value was constant, the r value p-NH2 decreased with the increase of the φ. This -0.5 0 0.5 1 behavior shows the independence of these values σ scale and the adequacy of Eq. (1). Fig. 1. Extended (Y-T) plots of -ΔEx of phenylboranylmethyl anions.
References
1. Nakata, K.; Fujio, M.; Nishimoto, K.; Tsuno, Y. J. Phys. Org. Chem. 2010, 23, 1057-1065.
CLA10
Computational Study of Substituent Effects on Gas-Phase Stabilities of Phenylboranylmethyl Anions K. Nakata,a,* and M. Fujiob a
b
Science Research Center, Hosei University, Tokyo, Japan Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, Japan *[email protected]
Stabilities of anions of aromatic compounds are governed by three kinds of electronic effects, and an extended Yukawa-Tsuno equation (1) was recently proposed to describe the substituent effects.1 −ΔE X = ρ (σ 0 + r − Δσ R− + sΔσ S )
(1)
0
The normal substituent constant (σ ) measures the basic electron-donating or -withdrawing ability for all ring substituents. The resonance ( Δσ R– ) and saturation ( Δσ s ) substituent constants measure the ability of through-resonance and saturation effects, respectively. Resultant r– and s values reveal the degree of through-resonance and saturation effects in a given system, respectively. To confirm the validity of Eq. (1) and reveal the physical meanings of the r– and s values, we report here the substituent effects on gas-phase stabilities of phenylboranylmethyl anions (1). Relative stabilities of ring-substituted 1 were determined as energy differences (ΔEX) of the reactions (2). φ
H C H + B X H
H +
H
X
φ 1
H C H B H
(2)
−ΔEx / kcal mol-1
The energies of respective species included in the reactions were calculated at the B3LYP/6-311 +G(2d,p) level of theory. Obtained substituent p-NO2 H H effects were accurately analyzed by Eq. (1) to H H C C p-NO B H B H give the r–=0.59. (Fig. 1) A significant 15 p-CN delocalization of the negative charge to the m-NO2 p-CHO X 1 X benzene π-electron system was observed in 1, m-CN 10 p-COMe although such the canonical form cannot be p-CF3 m-CHO m-CF3 drawn. A NBO analysis explained the throughρ = 16.59 m-COMe m-Cl r - = 0.59 resonance via the orbital interaction between the 5 m-F s = 0.65 p-Cl π-orbital of side chain and the π*-orbital of p-MeO-m-Cl R = 0.999 benzene. Substituent-effect analyses were further SD = 0.32 H m-MeO p-t-Bu performed for 1 of which the dihedral angle φ 0 m-Me :σ p-Me p-MeO : σ− between the benzene and side chain planes was p,m-Me2 m-Me2N – : σ0 p-Me2N fixed. While the s value was constant, the r value p-NH2 decreased with the increase of the φ. This -0.5 0 0.5 1 behavior shows the independence of these values σ scale and the adequacy of Eq. (1). Fig. 1. Extended (Y-T) plots of -ΔEx of phenylboranylmethyl anions.
References
1. Nakata, K.; Fujio, M.; Nishimoto, K.; Tsuno, Y. J. Phys. Org. Chem. 2010, 23, 1057-1065.
CLA10
