Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

Abstract

An ab initio theoretical method based on a triadic formula has been employed to calculate changes in proton affinities (PAs) after sequential substitution of C-H by C-phenyl in methylamine and in the N-methyl component of N-methylacetamide. The overall objective was to investigate the cause of the recently reported unexpected basicity-enhancing effect of the N-trityl group in several amines and in acetamide. The triadic method indicates that the increase in PA from NH 3 to CH 3 NH 2 is principally due to destabilisation of the lone pair, compensated to some degree by a smaller bond energy term. The increasing PAs along the series CH 3 NH 2 , PhCH 2 NH 2 , Ph 2 CHNH 2 and Ph 3 CNH 2 are mainly due to an increasing relaxation energy effect following increasing phenyl substitution, supported by increasing bond energy terms. Introduction of para-methoxy substituents in tritylamine would be calculated to result in small incremental increases in PA, in agreement with experimental findings. The PA of tricyclohexylmethylamine (233.6 kcal·mol -1 ) is calculated to be similar to that of trimethoxytritylamine (233.5 kcal·mol -1 ), a consequence of the destabilisation of the lone pair on nitrogen by the three bulky cyclohexyl groups. Results for acetamide indicate that protonation on oxygen is

Computational design of Brønsted neutral organic superbases—[3]iminoradialenes and quinonimines are important synthetic targets

“…84 We note in passing that this approach proved useful in rationalizing the substituent effects as well. [85][86][87][88] As a final remark, it should be mentioned that Koopmans' (IE) n Koop orbital energies were computed by the HF/ 6-311+G(2df,p)//B3LYP/6-31G(d) model. All calculations have been carried out by GAUSSIAN 03 program.…”

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

“…[74] We note in passing that this approach has proved useful in interpreting substituent effects too, as was convincingly shown recently. [75][76][77] As a final remark, it should be mentioned that Koopmans' (IE) n Koop orbital energies were computed using the HF/6-311+G(d,p)//B3LYP/6-31+G(d) model. All the calculations were carried out using the GAUSSIAN03 program.…”

“…It proved very useful in reproducing the trend in changes in proton affinities, as is now well documented. [65,77,90] For this purpose we employed a succinct description, yielding the changes in proton affinities relative to the predetermined gauge molecule, which in our case is the parent quinone 3 as a progenitor of all the quinoid systems. According to the triadic formula in Equation (5), the corresponding triad is given by Equation (7),…”

Hydride Affinities of Substituted Alkenes: Their Prediction by Density Functional Calculations and Rationalisation by Triadic Formula

“…The triadic (trichotomy) formula has some distinct advantages over more traditional ways of rationalizing the trend of changes in acidity and basicity over series of related compounds, as thoroughly discussed by Deakyne in a recent review, [35] and this approach has also proved useful in explaining the substituent effects and their influence on acidity and basicity. [36] It is gratifying that the triadic paradigm can be easily extended to hydride affinities, as shown recently in the case of borane (BH 3 ) derivatives. [37] Building on these results we consider here the HAs of the mono-substituted ethenes H 2 C=CHR (R = CH 3 , C 2 H 5 , C 3 H 7 , C 6 H 5 , CH=CH 2 , CN, NO 2 , F, NH 2 , OH and CF 3 ) in order to assess their influence on the hydride affinity of the parent molecule.…”