Khalil Andrew S, 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, Graz University of Technology , NAWI Graz., Stremayrgasse 9/Z2, Graz, Austria.
J Phys Chem A. 2017 Sep 7;121(35):6646-6651. doi: 10.1021/acs.jpca.7b05745. Epub 2017 Aug 28.
This combined experimental and theoretical study answers the question whether the intramolecular hydrogen-bond strength in amino alcohols is dependent on the ring size. For this purpose, the rotational spectrum of the 3-aminopropanol-HO van der Waals complex was recorded using Fourier-transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson A-reduction Hamiltonian. The experimental results are consistent with an ab initio conformation calculated at the MP2/6-311++G(d,p) level that involves the lowest energy 3-aminopropanol monomer and consists of a hydrogen bonding network. The calculated global minimum ab initio complex however comprises a higher energy monomer conformation of 3-aminopropanol. Upon complex formation with water, the O-H····N intramolecular hydrogen bond and OCCN backbone conformation of the lower energy monomer remain unchanged, in contrast to 2-aminoethanol. This behavior is consistent with the increasing strength of the intramolecular hydrogen bond of linear amino alcohols as a function of increasing chain length.
这项结合实验与理论的研究回答了氨基醇分子内氢键强度是否取决于环大小这一问题。为此，利用傅里叶变换微波光谱记录了3-氨基丙醇-HO范德华复合物的转动光谱，并将其拟合到沃森A约化哈密顿量的转动、四极耦合和离心畸变常数上。实验结果与在MP2/6-311++G(d,p)水平计算的从头算构象一致，该构象涉及能量最低的3-氨基丙醇单体，并由一个氢键网络组成。然而，计算得到的全局最小从头算复合物包含能量更高的3-氨基丙醇单体构象。与2-氨基乙醇相反，与水形成复合物时，低能量单体的O-H····N分子内氢键和OCCN主链构象保持不变。这种行为与线性氨基醇分子内氢键强度随链长增加而增强一致。
