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Crystal structures, Hirshfeld surface analysis and a computational study have been carried out on 2-oxo-2 H -chromene-3-carboxylates. Crystal structures are reported for ethyl R-2-oxo-2 H -chromene-3-carboxylate derivatives,  2a : R=6-Me,  2b : 7-Me,  2c : 7-Me,  2d : R=7-MeO. In contrast to 2-oxo-2H-chromene-3-carboxamides,  1 , in which classical intramolecular N–H···O hydrogen bonds stabilize planar structures and hinder rotation of the amido group out of the coumarin plane in  2 , without an equivalent hydrogen bond, there is a greater rotational freedom of the carboxylate group. The interplanar angles between the coumarin core and its attached –C(O)–R substituent in crystalline  2a ,  2b ,  2c  and  2d  are 10.41(6), 36.65(6), 10.4(2) and 5.64(6)°, respectively, with distances between the carbonyl oxygen atoms of 2.8255(16), 2.9278(16), 4.226(2) and 2.8328(14) Å, respectively. A theoretical study of molecular conformations was carried out at the M06-2X density level with the 6-31+G(d) and aug-cc-pVTZ basis sets, in methanol solution modeled by PCM, indicated that the most stable conformations had the carbonyl group of the ester in the plane of the coumarin core: the  s-cis  arrangement of the ester carbonyl and the 2-oxo moieties being the slightly more stable than the  s-trans  form by less than 0.5 kcal/mol. The experimental conformations of  2a  and  2d  match well the low energy  s-cis  arrangement, and  2c  matches the slightly lesser stable  s-trans  arrangement found in the theoretical study. A survey of the molecular conformations of more than 50 2 H -chromene-3-carboxylates derivatives in the CCDC data base indicated two distinct groupings of conformations,  s-cis  and  s-trans , each with interplanar angles &lt;30°.

zeitschrift für kristallographie - crystalline materials 

Crystal structures, Hirsfeld surface analysis and a computational study of four ethyl 2-oxo-2 H -chromene-3-carboxylate derivatives: a survey of organyl 2-oxo-2 H -chromene-3-carboxylate structures