To what extent can a conjugation between two pairs of peri‐nitro and peri‐amino groups be realized through the naphthalene core?

Abstract

Through-conjugation for a wide range of 1, 8-diamino-4,5-dinitronaphthalenes (N-acylated, N-alkylated, N,N 0 -bridged, N-heterocyclic, and N-deprotonated compounds) was for the first time quantified in solution by means of ultravioletvisible and proton nuclear magnetic resonance spectroscopy and compared with that of the simpler naphthalene and benzene push-pull systems. Surprisingly, an extent of conjugation in 1,8-diamino-4-nitro-and 1,8-diamino-4,5dinitronaphthalenes measured in dimethyl sulfoxide is commensurable. On the whole, the repulsive peri-interactions between the amino groups in systems with N-alkylated and N-deprotonated amino groups are more favorable for an effective D-p-A charge transfer than in N,N 0 -bridged compounds (perimidines, 2,3-dihydroperimidines and perimidin-2-ones). The best electron donors from peri-positions are pyrrolidin-1-yl and methylamido groups. The conclusions obtained from solution studies were deepened by solid-state X-ray experiments for a number of push-pull naphthalenes, including 6,7-dinitroperimidine N-anion and two representatives of 4,5-diaminonaphthalene-1,8-dicarbaldehydes. In particular, they helped to trace changes in the bond order redistribution and twisting of the naphthalene core. The latter reaches a record value of 27 for 4,5-dinitro-1,8-di(pyrrolidin-1-yl)naphthalene.

Aromaticity ofperi- andpara-Substituted Naphthalene-1-carbaldehyde. Comparison with 1-Nitronaphthalene

“…The HOMA value shows the medium aromaticity of the naphthalene rings; however, it is to note that the decrease of the aromaticity is greater than for 4,5-bis­(dimethylamino)-1,8-dicarbaldehyde. This observation is in accord with the statement of Ozeryanskiiet al . that the pyrrolidino group is a more effective π-electron acceptor than the dimethylamine group.…”

“…24,25 The through-resonance interactions in peri-substituted naphthalene derivatives were recently discussed. 17,21,22 In the previous paper, 17 we investigated the influence of throughspace and through-resonance interactions in the series of naphthalenes with amino and nitro substituents in peri and para positions on aromaticity of the aromatic rings expressed by HOMA index. As a measure of the quinoind-resonance structure we applied the ellipticity of the electron density at the bond critical point of C2−C3 (C6−C7) bonds in naphthalene aromatic ring obtained by topological analysis of the electron density in frame of QTAIM method.…”

“…When two substituents of opposite electron properties are included in the para position of the naphthalene ring, the through-resonance effect between the para substituents appears. ,− The through-resonance effect associated with a charge transfer from electron-donor to electron-acceptor group in para position results in an increase of the weight of canonical quinoid structure and a decrease of their aromaticity. ,− Naphthalene derivatives with π-donor and π-acceptor groups in the para -position belong to the family of push–pull compounds, widely studied due their application in optoelectronics and other functional materials . The push–pull interaction in the naphthalene derivatives also leads to the specific optical properties and their possible practical applications as a fluorescence switch, , as fluorofores in biological studies and in fluorescence microscopy, and recently in medical studies in positron-emission tomography. , …”

Substituents and Environment Influences on Aromaticity of peri- and para-Substituted Naphthalenes

“…The respective values of ε(r) are greater in comparison to the respective 1,8-bis(dialkyloamino)naphthalenes, which is in agreement with the statement of Ozeryanskii at al. 8 that the pyrrolidin-1-yl is a more effective electrondonor in comparison to the dialkylmethylamine group. The highest ε(r) value of the C2−C3 (0.2118) was found for the para-disubstituted ring in 1-pyrrolidino-2,4-dinitronaphthalene, where the HOMA value (0.4291) indicates a significant loss of the aromaticity.…”

“…4 and Ozeryanskii at al. 7, 8 The most striking effect is a decrease of the HOMA value to 0.5762 in optimized and to 0.4929 in the solid state molecule, indicating a considerable decrease of aromaticity in the para-disubstituted aromatic ring. The respective HOMA values for monosubstituted ring in this molecule are 0.6481 and 0.6909.…”