Mapping of N−C Bond Formation from a Series of Crystalline Peri‐Substituted Naphthalenes by Charge Density and Solid‐State NMR Methodologies

Abstract

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1JNC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1JNC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1JNC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å.

The Cambridge Structural Database and structural dynamics

“…Consider a quantum chemical calculation on the nucleophilic attack of cyanide ion to acetone, NC − + (CH 3 ) 2 C=O, as an example. It shows that the orbital overlap contribution is comparable to the electrostatic term long before NC − reaches the estimated transition state at d(NC…C) ∼ 1.98 Å ( Ríguez et al , 2023 ; Fernández et al , 2023 ; compare with the experimental estimate given in the paragraph on “Decay of tetrahedral intermediates” in Sec. III.C ).…”

Incipient Nucleophilic Attack on a Carbonyl Group Adjacent to a Stereogenic Centre in Peri Naphthalene Derivatives

“…[24] The studies on a series of peri-naphthalene and -acenaphthenes representing an aza-Michael reaction (Me 2 N/C=CZ 2 , Z = electron-withdrawing group), with interactions ranging from initial n-π* interaction to partially completed bond formation has led to the construction of a reaction pathway and to measurement of bonding charge density between reacting groups as the bond forms. [25,26] This area of 'Structural Correlation' was an important component of Jack's contribution to chemistry. [27] More recently the important role of O•••C=O n/π* interactions in determining protein structures, first highlighted in the peri-naphthalenes, has also been recognised.…”