Molecular Simulation of Hydrogen Bonds, Diels-Alder Reactions, Urethane Formation from Isocyanates andPhotochromism of Dithienylethenes byNew MOPAC2016 Hamiltonians and The Evaluation

Abstract

最近のMOPAC2016ハミルトニアンPM7を用いて, 基礎的な化学結合, 水素結合(Hb), 立体選択的Diels-Alder (DA) 反応, 実用的なイソシアネートのウレタン化反応そして光異性化反応等のシミュレーション解析を行い, その構造とエネルギー情報につき、実験値および他の計算値と比較評価した. 上記一部につき前報[1]では PM6法で可成りの理解は得られたが, 問題点のあることも指摘した. PM7での解析では、分子内、分子間の結合 距離とエネルギーの小さい変化の評価で向上が見られ, 分散力算出等の改善の有効性が示唆された. 例えば上記 反応2例では、より大きい水素結合エネルギー(E_Hb)と分子間相互作用エネルギー(E_Ln)の算出で安定錯体 (B)の存在推定と, より実験値に近い活性化エネルギー(E_a)が見積られ, Figure 1等の反応プロセスと遷移状態(TS)の評価改善が推定され, またBなどの低温での解析実験法を提案した. 簡便で定量性の改善された MOPAC2016は教育や実験の現場等で積極的活用が期待される.

Figures

Figure 1.

 PM7simulations of water dimer and methanol dimer structures (Å).

Figure 2.

 PM7 simulation of the (PhNCO + 2MeOH) reaction: The complex (B), transition state (TS: C), product (D) and relative energies (ΔH_f). (Each H_f energy (kcal mol⁻¹)). (subscript: Hb; Hydrogen bond, In; Interaction and a; activation).

Figure 3.

 IRC　data of urethane (D) formation via the complex (B) from the (PhNCO + 2MeOH) reaction.

Figure 4.

 PM7-TS simulation of DA reaction (BD + ET), and the complex (B), transition state (TS: C) and product (D) energies: relative energies ΔH_f (kcal mol⁻¹).

Figure 5.

 Stereoselective (CP + MA) DA reaction processes, and the two complexes (B_end, B_exo), transition states (TS_end, TS_exo), and products (D_end, D_exo).

Figure 6.

 Valence isomerization of substituted dithienylethenes (VIo._Ph, VIc._Ph) and (VIo._CHO, VIc._CHO).

Tables

Table 1. Comparison of the complex B, TS (C), and product D(a − f) structures in Figure 3 by PM7, PM6 and B3LYP/6-31+G (d,p) [3]

Table 2. Comparison of the energies (E_Hb, E_In and E_a in kcal mol⁻¹) in Figure 2 by PM7, PM6 and B3LYP/6-31+G (d,p) [3]

Table 3. Comparison of the CPU time and TS structures (a − f) by PM7, PM6, MP2-Full etc. for the reaction PhNCO + 2H₂O

Table 4. Comparison of the energies (E_In and Ea (kcal mol⁻¹)) in Figure 4 by PM7, PM7-TS, CBS-QB3 [7] and MP2-FULL etc., and two experimental data [8], [9]

Table 5. Comparison of the three energies (E_In, E_a and E_D) for DA stereoisomers in Figure 5 by PM7-TS and B3LYP/6-31+G (d,p) [3] etc.

Table 6. Thermal stability (ΔH_f) estimation of valence　isomers, (VIo_.Ph, VIc_.Ph) and (VIo_.CHO, VIc_.CHO) by PM7, B3LYP/6-31G* and PM6

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