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

Abstract

The influence of substituents and environment on the aromaticity of the naphthalene ring is shown for a series of peri-and para-substituted naphthalenes. Crystal structure geometries are compared with the single molecule structures in vacuum (optimized at the B3LYP/6-311++G** level) and with structures determined in media of different polarity. The harmonic oscillator model of aromaticity (HOMA) index of the naphthalene rings has been used to characterize the aromaticity of the investigated molecules. It has been shown that the ellipticity of the C2−C3 (C6−C7) bonds can be applied as a measure of participation of the quinoid resonance structure and through-resonance effect between the para-substituents. ■ INTRODUCTIONPeri-interaction in 1,8-disubstituted naphthalenes has attracted attention for a long time, due to their influence on physical and chemical properties of the compounds. 1−6 Two substituents in peri-positions of naphthalene are forced to be in close contact, generally closer than the sum of their van der Waals radii, leading to strong through-space interactionsattractive or repulsive depending on their properties. To release the steric strain, the substituents generally adopt nonplanar conformations. This through-space interaction leads to a change of exocyclic bonds and torsion angles and a disturbance of the naphthalene skeleton. When into the 4 and/or 5 position of the naphthalene ring having a pair of the peri-substituents in the 1,8 positions we introduce substituents with opposite electronic properties, the through-resonance effect may appear. 7,8 The through-resonance effectassociated with a charge transfer from electron-donor to electron-acceptor group in the para positionresults in an increase of the weight of the canonical quinoid structure. The electronic structure and geometry of the naphthalene derivatives with two pairs of peri substituents of opposite electronic properties in the para positions is the effect of compromise between the effects of through-space (peri) and through-bonds (through-resonance) interactions. 4,7,8 One of the best known groups of naphthalene derivatives, with substituents in peri and para positions, are 1,8-bis(dialkylamino)naphthalenes, called the "proton sponges". 4−6 Exceptional basicity of 1,8-bis(dimethylamino)-napthalene (pK a = 12.1 9 ) results from the repulsive steric and electrostatic interactions between the dimethylamino groups. The 1,8-bis(dialkylamino)naphthalenes additionally substituted with electron-accepting groups in 4,5 positions, called "the pushpull proton sponges", exhibit some interesting properties caused by a through-resonance (push−pull) interaction. 7,8 It was shown that these compounds are very sensitive to the solvent effect. 7,8,10 The through-space and through-bond interaction between the pairs of substituents in peri and para positions in the naphthalene ring affects both the π-electron delocalization and geometry of the aromatic ring. A consequence of these interactions is a change of aromaticity of the naphthalene ring. A π-e...

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

“…As can be seen from Figure 2, the ε 2−3 ellipticity values for naphthalene-1-carbaldehyde and its nitro analogous are closer to the values in nonsubstituted naphthalene (0.1621) 17 and are not sensitive to the rotation the functional group. For 4,5bis(dimethylamino)naphhtalene-1-carbaldehyde and 4,5-bis-(dimethylamino)-1-nitronaphthalene, where the through-resonance between the substituents in para position appears, the ε 2−3 value decreases with increasing α angle.…”

“…As it was shown previously, 17 information concerning the decrease of aromaticity and the weight of the resonance quinoide structure may be obtained from the ellipticity of the electron density at the bond critical point (BCP) for 2−3 (ε 2−3 ) and 6−7 (ε 6−7 ) bonds. 17 The ellipticity value is known to be dependent on the double-bond character of the bond and hence may be a measure of the weight of the quinoide resonance structure.…”

“…4,[6][7][8]10,12,15 In this work we have investigated the peri interaction between two formyl groups in the model structure of naphthalene-1,8-dicarbaldehyde and have compared them with the peri interaction in the previously investigated 1,8dinitronaphthalene. 17 S5, Figure S1a−c). The QTAIM method shows a possibility of the existence of attractive interactions only between the C and O atom in the formyl groups.…”

1 H and 13 C NMR spectral assignments of novel adamantyl and di-adamantyl derivatives of 1,2-dihydroxynaphthalenes, 1,8-dihydroxynaphthalenes, 2,3-dihydroxynaphthalenes, 2,6-dihydroxynaphthalenes and 2,7-dihydroxynaphthalenes

“…Despite the fact that since the discovery and development methods of preparation and isolation of various dihydroxynaphthalenes passed a long time, at present, each of the ten isomers continue to find more and more fields of application. Among them, 1,8‐dihydroxynaphthalene and their derivatives take a special place because the peri ‐interactions in 1,8‐substituted naphthalene skeleton have an influence on the physical and chemical properties of these compounds . In addition, currently, the properties of equatorenes [chiral polycyclic aromatic hydrocarbons containing bis(1‐adamantyl) groups at the peri ‐positions] were actively investigated, and in the case of 1,8‐bis(1‐adamantyl)naphthalene, a distortion of an aromatic ring system was determined .…”

“…Among them, 1,8-dihydroxynaphthalene and their derivatives take a special place because the peri-interactions in 1,8-substituted naphthalene skeleton have an influence on the physical and chemical properties of these compounds. [2,3] In addition, currently, the properties of equatorenes [chiral polycyclic aromatic hydrocarbons containing bis(1-adamantyl) groups at the peri-positions] were actively investigated, and in the case of 1,8-bis(1-adamantyl)naphthalene, a distortion of an aromatic ring system was determined. [4][5][6] Studies by NMR spectroscopy of various perieffects of naphthalene-containing compounds as well as analysis of influence of different-sized substituents on an aromaticity in hydroxynaphthalene system are an important topic in NMR literature.…”