Oresmaa Larisa, Haukka Matti, Vainiotalo Pirjo, Pakkanen Tapani A
University of Joensuu, Department of Chemistry, P.O. Box 111, FIN-80101 Joensuu, Finland.
J Org Chem. 2002 Nov 15;67(23):8216-9. doi: 10.1021/jo026126r.
The gas-phase proton affinities of 4,4'-di(R)-2,2'-bipyridines (R: H, Br, Cl, NO(2), Me) were determined by mass spectrometric measurements and by ab initio calculations at the HF/6-31G and MP2/6-31G levels of theory. The energy barriers for rotation about the central C-C bond were also studied computationally. Two minima were found for both unprotonated and protonated species, the global minima being at the trans planar and cis planar conformations, respectively. Local minima for the unprotonated compounds were at the cis nonplanar conformation and for the protonated compounds at the trans nonplanar. Two different proton affinity values were calculated for each compound by employing different conformations for the protonated species. The computational values were in good agreement with the experimental proton affinities. Substituents affect the proton affinity according to their ability to withdraw or to donate electrons, halogen and nitro-substituted bipyridines having a lower proton affinity and methyl-substituted bipyridine having a higher proton affinity than 2,2'-bipyridine itself.
通过质谱测量以及在 HF/6 - 31G 和 MP2/6 - 31G 理论水平下的从头算计算，测定了 4,4'-二（R）-2,2'-联吡啶（R：H、Br、Cl、NO₂、Me）的气相质子亲合势。还通过计算研究了围绕中心 C - C 键旋转的能垒。对于未质子化和质子化的物种都发现了两个极小值，全局极小值分别处于反式平面和顺式平面构象。未质子化化合物的局部极小值处于顺式非平面构象，质子化化合物的局部极小值处于反式非平面构象。通过采用质子化物种的不同构象，为每种化合物计算了两个不同的质子亲合势值。计算值与实验质子亲合势吻合良好。取代基根据其吸电子或供电子能力影响质子亲合势，卤素和硝基取代的联吡啶的质子亲合势低于 2,2'-联吡啶本身，而甲基取代的联吡啶的质子亲合势高于 2,2'-联吡啶本身。
