Mononitration of 9-substituted ethanoanthracenes, bearing Me, But, F, Br, I, OMe , NO2, CN, CHO or CO2Me substituents at the bridgehead carbon, was found to occur exclusively at the β-positions of the aromatic ring. The mononitro products were isolated, identified by 1H n.m.r. spectroscopy, and their relative proportions were estimated by quantitative g.l.c . and/or by 1H n.m.r. spectroscopy. For all the above substrates the proportion of nitration at the β-position meta to the bridgehead carbon bearing the substituent [to give compounds of the general form (4)] was greater than the proportion of nitration at the corresponding β-position para to the bridgehead substituent [to give compounds of the general form (3)]. Whilst the preferential nitration at the β-positions of the aromatic rings is consistent with the previously reported nitration of 9,10-dihydro-9,10-ethanoanthracene (2a) itself, no observations of this preferential meta attack have been made previously. No correlation could be made of this behaviour with available substituent parameters for the widely sterically and electronically disparate set of substituents used in this study, and the origin of this preferential attack remains unclear. Dinitration in this system was studied only superficially. The influence of the bridgehead substituent together with that of the nitro group already present on one aromatic ring appear to combine with quite unpredictable results in orienting the position of attack of the incoming nitro group onto the other (non-nitrated) aromatic ring.
研究发现,桥头碳上含有 Me、But、F、Br、I、OMe、NO2、CN、CHO 或 CO2Me 取代基的 9-取代乙蒽的单硝化作用只发生在芳香环的β位。单硝基产物被分离出来,并通过 1H n.m.r. 光谱进行鉴定,其相对比例则通过定量 g.l.c .和/或 1H n.m.r. 光谱进行估算。对于上述所有底物,在含有取代基的桥头碳的β-元位置上的硝化比例[得到一般形式 (4) 的化合物]大于在桥头取代基的相应β-对位位置上的硝化比例[得到一般形式 (3) 的化合物]。虽然芳香环 β 位的优先硝化与之前报道的 9,10-二氢-9,10-乙桥蒽 (2a) 本身的硝化一致,但之前并没有观察到这种优先元攻击。由于本研究中使用的取代基在立体和电子方面存在很大差异,因此无法将这种行为与现有的取代基参数联系起来,而且这种优先偏置的起源仍不清楚。 对该体系中的二硝化作用仅进行了表面研究。桥头取代基和一个芳香环上已经存在的硝基的影响,似乎在确定进入的硝基对另一个(未硝化的)芳香环的攻击位置时,产生了难以预测的结果。