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

Gregory J Rees,Jonathan R Yates,Mark E Smith,Alberth Lari,John V Hanna,Stephen P Day,Peter Gierth,Mateusz B Pitak,Kristian Barnsley,Simon J Coles,John D Wallis

doi:10.1002/anie.202111100

Abstract

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1 J NC 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 sp 2 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 1 J NC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1 J NC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å.

Highlights

The concept of structure in chemistry implies the existence of bonds that can persist over a range of inter-nuclearDr G
Charge density determinations were made from X-ray diffraction data on high-quality crystals of 1–6 at 100 K, with data for 6 collected using a synchrotron source (Diamond Light Source) on account of small crystal size
The corresponding crystal structures for S1–S2 and 1–6 have been used to calculate, via density functional theory (DFT), the 1JNC couplings between 15N and 13C atoms located at either end of the peri interaction/partial bond to characterise the interaction across the Me2N···C bridge

Summary

Introduction

The concept of structure in chemistry implies the existence of bonds that can persist over a range of inter-nuclearDr G. We measure the degree of covalent bond formation in a series of crystalline organic compounds using two complementary solid-state methods, X-ray crystallography and NMR which are both supported by density functional theory (DFT) calculations.

Results

Conclusion