title: An acyclic trialkylamine virtually planar at nitrogen. Some chemical consequences of nitrogen planarity.
abstract: The synthesis of the exceedingly congested amine tris(1,3-dihydroxy-2-propyl)amine, 9, was achieved in 47- 51% overall yield. The nitrogen atom of 9 is virtually planar; it is 0.082 A out of the plane defined by the three attached carbons. The corresponding out-of-plane measurement is 0.282 A for triisopropylamine and ca. 0.4 A for uncongested trialkylamines. The N-C bonds of 9 are quite short, despite the steric congestion. The conjugate acid of 9 (viz., 9H(+)) is very strong: pK(a) = 3.08 (cf. Et(3)NH(+) pK(a) = 10.7). Comparison with suitable model compounds suggests 9 is less basic than predicted by ca. 1.5 pK(a) units. The structure of 9H(+)Cl(-) was determined by X-ray crystallography. Here too, the nitrogen is severely flattened relative to ordinary ammonium cations. In 9H(+)Cl(-), the proton on the nitrogen of 9H(+) forms three intramolecular hydrogen bonds to hydroxyl groups, i.e., a so-called trifurcated hydrogen bond. The NH...O lengths in 9H(+) are slightly shorter than comparable trifurcated hydrogen bonds. Cyclic voltammetry (CV) on 9 finds E(1/2)(ox) 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 9 is reversible on the CV time scale. The (15)N NMR chemical shift of the essentially planar nitrogen atom of 9 is discussed.
authors.affiliation: Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, USA.
authors.forename: Yuanping
authors.initials: Y
authors.lastname: Jie
authors.forename: Peter
authors.initials: P
authors.lastname: Livant
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Minmin
authors.initials: M
authors.lastname: Yang
authors.forename: Wei
authors.initials: W
authors.lastname: Zhu
authors.forename: Vince
authors.initials: V
authors.lastname: Cammarata
authors.forename: Philip
authors.initials: P
authors.lastname: Almond
authors.forename: Tyler
authors.initials: T
authors.lastname: Sullens
authors.forename: Yu
authors.initials: Y
authors.lastname: Qin
authors.forename: Eric
authors.initials: E
authors.lastname: Bakker