Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
Phys Chem Chem Phys. 2011 Dec 7;13(45):20380-92. doi: 10.1039/c1cp22065a. Epub 2011 Oct 13.
Vibrational spectra of the conjugate acid of Me(2)NCH(2)CH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethylputrescine) have been examined in the gaseous and crystalline phases using Infrared Multiple Photon Dissociation (IRMPD) spectroscopy, Inelastic Neutron Scattering (INS), and high pressure Raman spectroscopy. A band observed near 530 cm(-1) is assigned to the asymmetric stretch of the bridging proton between the two nitrogens, based on deuterium substitution and pressure dependence. The NN distance measured by X-ray crystallography gives a good match to DFT calculations, and the experimental band position agrees with the value predicted from theory using a 2-dimensional potential energy surface. The reduced dimensionality potential energy surface, which treats the ion as though it possesses a linear NHN geometry, shows low barriers to proton transit from one nitrogen to the other, with zero point levels close to the barrier tops. In contrast, two other related systems containing strong hydrogen bonds do not exhibit the same spectroscopic signature of a low barrier hydrogen bond (LBHB). On the one hand, the IRMPD spectra of the conjugate acid ions of the amino acid N,N,N',N'-tetramethylornithine (in which the two nitrogens have different basicities) show fewer bands and no comparable isotopic shifts in the low frequency domain. On the other hand, the IRMPD spectrum of the shorter homologue Me(2)NCH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethyl-1,3-propanediamine), for which the NHN bond angle deviates substantially from linearity, displays more than one band in the 1100-1400 cm(-1) domain, which vanish as a consequence of deuteration.
已使用红外多光子解离（IRMPD）光谱、非弹性中子散射（INS）和高压拉曼光谱研究了 Me(2)NCH(2)CH(2)CH(2)CH(2)NMe(2)（N，N，N'，N'-四甲基腐胺）的共轭酸在气态和晶相中的振动光谱。基于氘取代和压力依赖性，将在 530cm(-1)附近观察到的带分配给两个氮之间桥接质子的不对称伸展。通过 X 射线晶体学测量的 NN 距离与 DFT 计算很好地匹配，实验带位置与使用二维势能面从理论预测的值一致。处理离子为线性 NHN 几何形状的简化二维势能面显示质子从一个氮到另一个氮的迁移具有低势垒，零点水平接近势垒顶部。相比之下，另外两个包含强氢键的相关体系没有表现出相同的低势垒氢键（LBHB）的光谱特征。一方面，氨基酸 N，N，N'，N'-四甲基鸟氨酸的共轭酸离子的 IRMPD 光谱显示出较少的带，并且在低频域中没有可比的同位素位移。另一方面，较短的同系物 Me(2)NCH(2)CH(2)CH(2)NMe(2)（N，N，N'，N'-四甲基-1,3-丙二胺）的 IRMPD 光谱显示出 1100-1400cm(-1) 域中的多个带，氘化后这些带消失。
