Graduate Program in Biophysics, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706-1534, USA.
Chem Commun (Camb). 2013 Sep 25;49(74):8166-8. doi: 10.1039/c3cc44573a.
Carbonyl-carbonyl (C=O···C'=O') interactions are ubiquitous in both small and large molecular systems. This interaction involves delocalization of a lone pair (n) of a donor oxygen into the antibonding orbital (π*) of an acceptor carbonyl group. Analyses of high-resolution protein structures suggest that these carbonyl-carbonyl interactions prefer to occur in pairs, that is, one donor per acceptor. Here, the reluctance of the acceptor carbonyl group (C'=O') to engage in more than one n→π* electron delocalization is probed using imidazolidine-based model systems with one acceptor carbonyl group and two equivalent donor carbonyl groups. The data indicate that the electrophilicity of the acceptor carbonyl group is reduced when it engages in n→π* electron delocalization. This diminished electrophilicity discourages a second n→π* interaction with the acceptor carbonyl group.
羰基-羰基（C=O···C'=O'）相互作用在小分子和大分子系统中都普遍存在。这种相互作用涉及到供体氧的孤对电子（n）的离域到受体羰基的反键轨道（π*）中。对高分辨率蛋白质结构的分析表明，这些羰基-羰基相互作用倾向于成对发生，即每个受体有一个供体。在这里，使用基于咪唑烷的模型系统，该系统具有一个受体羰基和两个等效的供体羰基，探究了受体羰基（C'=O'）参与不止一次 n→π电子离域的不情愿。数据表明，当受体羰基参与 n→π电子离域时，其亲电性降低。这种降低的亲电性阻碍了与受体羰基的第二次 n→π*相互作用。
