Crystal structures, Hirshfeld analysis, and energy framework analysis of two differently 3'-substituted 4-methylchalcones: 3'-(N=CHC 6 H 4 -p-CH 3 )-4-methylchalcone and 3'-(NHCOCH 3 )-4-methylchalcone.

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a p-methyl substitution on the 3-Ring, but differ with respect to the m-substitution on the 1-Ring. Their systematic names are (2E)-3-(4-methylphenyl)-1-(3-{[(4-methylphenyl)methylidene]amino}phenyl)prop-2-en-1-one (C 24 H 21 NO) and N-{3-[(2E)-3-(4-methylphenyl)prop-2-enoyl]phenyl}acetamide (C 18 H 17 NO 2 ), which are abbreviated as 3'-(N=CHC 6 H 4 -p-CH 3 )-4-methylchalcone and 3'-(NHCOCH 3 )-4-methylchalcone, respectively. Both chalcones represent the first reported acetamide-substituted and imino-substituted chalcone crystal structures, adding to the robust library of chalcone structures within the Cambridge Structural Database. The crystal structure of 3'-(N=CHC 6 H 4 -p-CH 3 )-4-methylchalcone exhibits close contacts between the enone O atom and the substituent arene ring, in addition to C...C interactions between the substituent arene rings. The structure of 3'-(NHCOCH 3 )-4-methylchalcone exhibits a unique interaction between the enone O atom and the 1-Ring substituent, contributing to its antiparallel crystal packing. In addition, both structures exhibit π-stacking, which occurs between the 1-Ring and R-Ring for 3'-(N=CHC 6 H 4 -p-CH 3 )-4-methylchalcone, and between the 1-Ring and 3-Ring for 3'-(NHCOCH 3 )-4-methylchalcone.