Experimental NMR and DFT Studies of Persistent Carbocations Derived from Hetero-Polycyclic Aromatic Hydrocarbons Containing Oxygen Atom: Dibenzo[<i>b</i>,<i>d</i>]furan, Benzo[<i>b</i>]naphtho[1,2-<i>d</i>]furan, Benzo[<i>b</i>]naphtho[2,3-<i>d</i>]furan, Benzo[<i>b</i>]naphtho[2,1-<i>d</i>]furan, and Dinaphtho[2,1-<i>b</i>:1′,2′-<i>d</i>]furan
作者:Takao Okazaki、Madoka Nakagawa、Toshikazu Kitagawa、Kenneth K. Laali
DOI:10.1246/bcsj.20140182
日期:2014.11.15
Persistent protonation carbocations generated from hetero-PAHs containing oxygen atoms in their aromatic rings, dibenzo[b,d]furan (5), benzo[b]naphtho[1,2-d]furan (6), benzo[b]naphtho[2,3-d]furan (7), benzo[b]naphtho[2,1-d]furan (8), and dinaphtho[2,1-b:1′,2′-d]furan (9), were directly observed by NMR measurements in superacid. Compound 5 was protonated mainly at C(2) in FSO3H–SbF5 (1:1) or (4:1)/SO2ClF, and 6, 8, and 9 were protonated exclusively at C(5) in CF3SO3H or FSO3H/SO2ClF, whereas 7 was protonated at C(6) and C(11) to give two species in FSO3H/SO2ClF. Surprisingly, compound 5 resists protonation in FSO3H/SO2ClF to show NMR spectra corresponding to that of the intact material. Positive charge delocalization mapping for carbocations based on experimental Δδ13C values indicates limited delocalization in these systems. The chemical shifts and charge delocalization modes derived by DFT calculations agreed with the experimental results.
在超强酸中,通过NMR测量直接观察到了含有氧原子在其芳环上的杂PAHs产生的持久质子化碳正离子,包括二苯并[b,d]呋喃(5)、苯并[b]萘并[1,2-d]呋喃(6)、苯并[b]萘并[2,3-d]呋喃(7)、苯并[b]萘并[2,1-d]呋喃(8)和二萘并[2,1-b:1′,2′-d]呋喃(9)。化合物5在FSO3H–SbF5(1:1)或(4:1)/SO2ClF中主要在C(2)位质子化,而6、8和9在CF3SO3H或FSO3H/SO2ClF中仅在C(5)位质子化,而7在FSO3H/SO2ClF中在C(6)和C(11)位质子化,形成两种物质。令人惊讶的是,化合物5在FSO3H/SO2ClF中抗拒质子化,呈现出与完整物质相对应的NMR谱图。基于实验Δδ13C值的碳正离子正电荷离域化映射表明这些体系中的离域化有限。DFT计算得出的化学位移和电荷离域化模式与实验结果一致。