Syntheses, crystal structures, and polymorphism of quaternary pyrrolidinium chlorides

Abstract

The syntheses, properties, and X-ray crystal structures of 1-methyl-1-propylpyrrolidinium chloride1, 1-allyl-1-methylpyrrolidinium chloride2, and 1-methyl-1-propargylpyrrolidinium chloride3 are described. Colorless plates of 1 (C₈H₁₈ClN) crystallize in the orthorhombic space groupPnab with Z = 8 and unit cell parameters a = 10.0354(11) Å, b = 13.254(2) Å, c = 14.6231(16) Å. Colorless prisms of 2 (C₈H₁₆ClN) crystallize in the monoclinic space groupP2₁/c with Z = 4 and unit cell parameters a = 6.4857(10) Å, b = 12.005(3) Å, c = 12.526(2) Å, and β=102.746(13)°. Colorless needles of 3 (C₈H₁₄ClN) crystallize in the monoclinic space groupP2₁/n with Z = 4 and unit cell parameters a = 8.4849(14) Å, b = 8.1271(16) Å, c = 13.501(2) Å, and β=100.408(13)°. The five-membered ring adopts a twisted conformation in 1 but an N-envelope in 2 and 3. The salts form networks of weak C–H^…Cl⁻hydrogen bonds. Hot stage microscopy, differential scanning calorimetry and temperature-controlled X-ray powder diffractometry revealed that each of the three compounds exists in at least two different crystal forms.