An Acyclic Trialkylamine Virtually Planar at Nitrogen. Some Chemical Consequences of Nitrogen Planarity
Yuanping Jie
Peter Livant
Hui Li
Minmin Yang
Wei Zhu
Vince Cammarata
Philip Almond
Tyler Sullens
Yu Qin
Eric Bakker
10.1021/jo100628v.s002
https://acs.figshare.com/articles/dataset/An_Acyclic_Trialkylamine_Virtually_Planar_at_Nitrogen_Some_Chemical_Consequences_of_Nitrogen_Planarity/2755963
The synthesis of the exceedingly congested amine tris(1,3-dihydroxy-2-propyl)amine, <b>9</b>, was achieved in 47− 51% overall yield. The nitrogen atom of <b>9</b> is virtually planar; it is 0.082 Å out of the plane defined by the three attached carbons. The corresponding out-of-plane measurement is 0.282 Å for triisopropylamine and ca. 0.4 Å for uncongested trialkylamines. The N−C bonds of <b>9</b> are quite short, despite the steric congestion. The conjugate acid of <b>9</b> (viz., <b>9</b>H<sup>+</sup>) is very strong: p<i>K</i><sub>a</sub> = 3.08 (cf. Et<sub>3</sub>NH<sup>+</sup> p<i>K</i><sub>a</sub> = 10.7). Comparison with suitable model compounds suggests <b>9</b> is less basic than predicted by ca. 1.5 p<i>K</i><sub>a</sub> units. The structure of <b>9</b>H<sup>+</sup>Cl<sup>−</sup> was determined by X-ray crystallography. Here too, the nitrogen is severely flattened relative to ordinary ammonium cations. In <b>9</b>H<sup>+</sup>Cl<sup>−</sup>, the proton on the nitrogen of <b>9</b>H<sup>+</sup> forms three intramolecular hydrogen bonds to hydroxyl groups, i.e., a so-called trifurcated hydrogen bond. The NH···O lengths in <b>9</b>H<sup>+</sup> are slightly shorter than comparable trifurcated hydrogen bonds. Cyclic voltammetry (CV) on <b>9</b> finds <i>E</i><sub>1/2</sub><sup>ox</sup> is 0.88 V, which is consistent with the inductive effect of the 1,3-dihydroxy-2-propyl groups attached to nitrogen. It is also observed that the electrochemical oxidation of <b>9</b> is reversible on the CV time scale. The <sup>15</sup>N NMR chemical shift of the essentially planar nitrogen atom of <b>9</b> is discussed.
2010-07-02 00:00:00
trifurcated hydrogen bonds
CV time scale
15 N NMR chemical shift
intramolecular hydrogen bonds
9 H
Et 3NH pKa
trifurcated hydrogen bond
nitrogen atom
1.5 pKa units
Nitrogen PlanarityThe synthesis