Hohl Jenna A, Harris Michael W, Strasser Nina, Kelterer Anne-Marie, Lavrich Richard J
Department of Chemistry and Biochemistry , College of Charleston , 66 George Street , Charleston , South Carolina 29424 , United States.
Institute of Physical and Theoretical Chemistry, NAWI Graz , Graz University of Technology , Stremayrgasse 9/Z2 , 8010 Graz , Austria.
J Phys Chem A. 2018 Nov 1;122(43):8505-8510. doi: 10.1021/acs.jpca.8b05888. Epub 2018 Oct 22.
We seek to determine the effect of competing intermolecular hydrogen bonds from water on the preferred conformation of 4-aminobutanol (4AB) monomers stabilized by intramolecular hydrogen bonds. Toward this end, the rotational spectrum of the 4-aminobutanol-HO complex was recorded using Fourier transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson S-reduction Hamiltonian. The experimental results are consistent with a 4AB-water complex that preserves the intramolecular hydrogen bond within the 4AB monomer and forms a single intermolecular bond with water acting as a donor. The experimental monomer structure agrees well with the lowest energy conformation calculated at the MP2/6-311++G(d,p) level of theory. Upon complex formation and the introduction of competing intermolecular bonds from water, only small changes in the OH···N intramolecular hydrogen bond and backbone torsional angles of the 4-aminobutanol monomer are observed. Similar small changes were observed for the shorter chain 3-aminopropanol amino alcohol monomer when complexed with water, in contrast to the 2-aminoethanol-HO complex. In the latter, a large change in the backbone torsional angle and a breaking of the intramolecular hydrogen bond were observed. Thus, extending the methylene chain results in an increase in the strength of the intramolecular hydrogen bond in unbranched amino alcohols.
我们试图确定来自水的竞争性分子间氢键对由分子内氢键稳定的4-氨基丁醇（4AB）单体的优选构象的影响。为此，使用傅里叶变换微波光谱记录了4-氨基丁醇-HO络合物的转动光谱，并将其拟合到沃森S-约化哈密顿量的转动、四极耦合和离心畸变常数。实验结果与一个4AB-水络合物一致，该络合物保留了4AB单体中的分子内氢键，并与作为供体的水形成了一个单一的分子间键。实验得到的单体结构与在MP2/6-311++G(d,p)理论水平计算出的最低能量构象吻合良好。在形成络合物并引入来自水的竞争性分子间键后，仅观察到4-氨基丁醇单体的OH···N分子内氢键和主链扭转角有微小变化。与2-氨基乙醇-HO络合物相比，当较短链的3-氨基丙醇氨基醇单体与水络合时也观察到了类似的微小变化。在后者中，观察到主链扭转角有很大变化且分子内氢键断裂。因此，延长亚甲基链会导致直链氨基醇中分子内氢键强度增加。
