(N)H...O=(C) dN...O dC=O Reference [Å] 4-Chloro-2-formyl-3-methyl-pyrrole R=H; R3=CH3; R4=Cl; R5=H 1.904 2.807 1.222 [110] 2-Formyl-3-methyl-pyrrole R=H; R3=CH3; R4=; R5=H 1.883 2.806 1.234 [110] 3-Methoxypyrrole-2-carbaldehyde R=H; R3=OCH3; R4=H; R5=H 1.816 2.797 1.223 [111] Methyl 2-Formylpyrrole-3-carboxylate R=H; R3=COOCH3; R4=H; R5=H 1.966 2.842 1.226 [111] N,N-Dimethyl-1H-pyrrole-2-carboxamide R=N(CH3)2; R3=H; R4=H; R5=H 1.909 2.817 1.246 [112] Methyl 5-methyl-3,4-diphenyl-1H-pyrrole-2-carboxylate R=OCH3; R3=C6H5; R4= C6H5; R5=CH3 1.99 2.829   [85] Diethyl 5-methylpyrrole-2,3-dicarboxylate R=OC2H5; R3= OC2H5; R4= H; R5=CH3 1.911 2.933 1.214 [113] Ethyl 4-dodecyl-3,5-dimethyl-1H-pyrrole-2-carboxylate R=OC2H5; R3= CH3; R4= C12H25; R5=CH3 1.995 2.85 1.212 [114] 4-Ethyl-3,5-dimethyl-1H-pyrole-2-carboxylic acid ethyl ester R=OC2H5; R3= CH3; R4= C2H5; R5=CH3 2.036 2.86 1.224 [115] Ethyl 4-acetyl-3,5-dimethyl-1H-pyrrole-2-carboxylate R=OC2H5; R3= CH3; R4= COCH3; R5=CH3 2.00 2.86 1.216 [116] 2-Trifluoroacetyl-5-trifluoromethylpyrrole R=CF3; R3= H; R4= H; R5=CF3 2.015 2.860 1.219 [117] Pyrrole-2-carboxylic acid R=OH; R3= H; R4= H; R5=H 2.18 2.997 1.23 [84] Dimethyl 3,5-dimethylpyrrole-2,4-dicarboxylate R=OCH3; R3= CH3; R4= OCH3; R5=CH3 2.08 2.863 1.219 [118] Pyrrole-2-carboxamide R=NH2; R3= H; R4= H; R5=H 2.207 2.987 1.249 [69] 1-(2-Pyridyl)-1-(2-pyrrolyl)methanone R=C5NH4; R3= H; R4= H; R5=H 2.045 2.86 1.238 [119] 2-Acetylpyrrole R=CH3; R3= H; R4= H; R5=H 1.983 2.863 1.227 [120] 4-Iodo-1H-pyrrole-2-carbaldehyde R=H; R3= H; R4= I; R5=H 1.996 2.842 1.216 [121] Ethyl 5-formyl-3,4-dimethyl-1H-pyrrole-2-carboxylate R=OC2H5; R3= CH3; R4= CH3; R5=CHO 2.07 2.919 1.193 [122] Dimethyl 3,4-diiodo-1H-pyrrole-2,5-dicarboxylate R=OCH3; R3= I; R4= I; R5= COOCH3 2.114 2.936 1.195 [123] (4-Fluorophenyl)(1H-pyrrol-2-yl)methanone R=C6H4I; R3= H; R4= H; R5= H 2.056 2.865 1.236 [124] 4-Ethyl-3,5-dimethyl-1H-pyrrole-2-carbaldehyde R=H; R3= CH3; R4= C2H5; R5= COOCH3 2.085 2.889 1.226 [125] Phenyl(3,4,5-trimethyl-1H-pyrrol-2-yl)methanone R=C6H5; R3= CH3; R4= CH3; R5= CH3 2.034 2.890 1.24 [126]

Table 3: The hydrogen-bonding geometry [Å] of the 2-acypyrrole dimeric aggregates in solid phase. Data were taken from the structural information collected in the Cambridge Structural Database (CSD).