Abstract

The crystal structure is reported for 2,7-dimethoxy-3-(1-naphthoyl)naphthalene (1), C23H17O3, one of β-aroylated naphthalene compounds.
In crystal, two naphthalene ring moieties of respective molecules are non-coplanarly located to each other, and two molecules are nested
inside one another through a pair of C–H···π hydrogen-bonding interactions (C–H···Cg = 2.73 Å) forming a dimeric molecular aggregate.
Each dimeric molecular aggregate is linked with four adjacent dimers by regular-squarely directed four (sp3
)C–H···OCH3 hydrogen bonds
between the methoxy groups (C–H···O = 2.50 Å) forming two-dimensionally spread plane. The planes are stacked into piles of layers along
ac diagonal. On the other hand, the β-aroylated naphthalene homologues, 3-benzoylated naphthalene derivative I and 3-(2-naphthoylated)
one II, are proved to take unidimensional molecular accumulation. Though each dimeric molecular aggregate has four identical
interactions between adjacent dimeric molecular aggregates in crystal of homologue I, the rectangular, i.e., non-regular-square aligned
situation of four interactions makes the linkage of each aggregate with only two adjacent dimers resulting in ribbon structure. In crystal of
homologue II, molecules are stacked without formation of dimeric aggregates in columnar structure. On the basis of the results of
systematic comparison of molecular packing structure and effective noncovalent-bonding interactions among title compound 1 and the βaroylated naphthalene homologues I and II, the presence of large difference in strength of intermolecular interactions, i.e., predominant or
apparently sole functioning of either C–H···O hydrogen bond or C–H···π hydrogen-bonding interaction induces only unidimensional
molecular accumulation, e.g., ribbon-like alignment composed of dimeric molecular aggregates or columnar assembling of molecules. 1
H
NMR spectra suggest that conformational interconversion behaviour of title compound 1 through rotation around two kinds of C–C bonds
in solution is disturbed rather largely compared to two homologous compounds I and II. Spatial organization characteristics of single
molecular and molecular packing structures of β-aroylated naphthalene homologues in crystal are comparatively analyzed along with those
in solution for the sake of elucidation of relationship among spatial organization, noncovalent bonding intermolecular interaction in crystal,
and steric factors in solution.

Key words: Non-classical hydrogen-bonding interaction, molecular motif, dimeric molecular aggregates, two-dimensionally spread layer