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首页> 外文期刊>Chemical Physics: A Journal Devoted to Experimental and Theoretical Research Involving Problems of Both a Chemical and Physical Nature >On the structure and spectroscopic properties of bispidine, N,N'-dimethylbispidine and a bis-bispidine macrocycle
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On the structure and spectroscopic properties of bispidine, N,N'-dimethylbispidine and a bis-bispidine macrocycle

机译：双联吡啶，N，N'-二甲基双联吡啶和双联双吡啶大环的结构和光谱性质

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摘要

The equilibrium conformations of bispidine and its N,N'-dimethyl derivative were investigated with the ab initio MP2 formalism and the density functional theory (DFT) ansatz B3LYP. For bispidine, the chair-chair (cc) (exo, endo) is the most stable conformer. On the contrary, for its N,N'-dimethyl derivative, the energy difference between the cc and chair-boat (cb) conformers is small, allowing for conformational mobility of the bicyclo rings. For tetraaza-macrocycle with four nitrogen lone pair orbitals (LPOs) pointing into the molecular cavity, the C_(2h) structure with stepped ethylene bridges is preferred over the twisted structure of D_2 symmetry. Mono- and di-protonated forms of this base are characterized by intramolecular asymmetric hydrogen bonds. All the theoretical conformational predictions are consistent with the available experimental results. The NMR chemical shifts, calculated by the continuous set of gauge transformations (CSGT) formalism with the DFT/B3LYP method, are fairly consistent with NMR observation. The He(I) photoelectron (PE) spectra were measured and assigned by means of ab initio outer valence Green's function (OVGF) calculations. The predominance of the lowest energy conformation of bispidine and tetraaza-macrocycle is supported by the spectroscopic results. The conformational situation for N,N'-dimethyl-bispidine is more complex. Whereas its NMR spectrum indicates a predominance of the cc conformer in THF-d_8 solution, the vibrational and PE spectra should be interpreted in terms of a mixture of the cc and cb conformers in the neat liquid and gas-phase.
机译：使用从头算的MP2形式和密度泛函理论（DFT）ansatz B3LYP，研究了联吡啶及其N，N'-二甲基衍生物的平衡构象。对于联吡啶，椅子（CC）（exo，endo）是最稳定的构型。相反，对于其N，N'-二甲基衍生物，cc和椅船（cb）构象异构体之间的能量差很小，从而允许双环的构象迁移。对于具有四个指向分子腔的氮孤对轨道（LPO）的四氮杂大环，具有D_2对称性的扭曲结构优选具有阶梯式乙烯桥的C_（2h）结构。该碱基的单和双质子化形式的特征是分子内不对称氢键。所有理论构象预测均与可用的实验结果一致。 NMR化学位移是通过DFT / B3LYP方法通过连续的一组规范变换（CSGT）形式主义计算得出的，与NMR观察结果相当一致。测量了He（I）光电子（PE）光谱，并通过从头计算外价格林函数（OVGF）进行了计算。光谱结果支持了联吡啶和四氮杂-大环的最低能量构象的优势。 N，N'-二甲基-双吡啶的构象情况更为复杂。尽管其NMR光谱表明THF-d_8溶液中cc构象异构体占优势，但振动和PE光谱应以纯液相和气相中cc和cb构象异构体的混合物来解释。

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