Conformations and Structures of N,N’-Bis(2-methoxybenzylidene)- 1,3-diamino-propanol and N,N’-Bis(3-methoxybenzylidene)-1,3- diamino-propanol

Abstract

N,N’-bis(2-methoxybenzylidene)-1,3-diamino-propanol (C₁₉H₂₂N₂O₄) 1 and N,N’-bis(3-methoxybenzylidene)- 1,3-diamino-propanol (C₁₉H₂₂N₂O₄) 2 have been investigated by X-ray analysis and AM1 semi-empirical quantum mechanical method. 1 is in the monoclinic space group C2/c with a = 33.694(6), b = 6.735(1), c = 17.681(3) Å , β = 114.72(2)°, V = 3645(1) ų, Z = 8, D_c = 1.248 mg cm⁻³ and μ(Mo-K_α ) = 0.088 mm⁻¹. 2 is in the monoclinic space group C2/c with a = 19.173(4), b = 7.626(2), c = 11.788(2) Å , β = 91.72(2)°, V = 1722.8(6) ų, Z = 4, D_c = 1.320 mg cm⁻³ and μ(Mo-K_α ) = 0.093 mm⁻¹. The crystal structures of 1 and 2 were solved by direct methods and refined to R = 0.053 for 1 and R = 0.041 for 2. Both molecules are not planar and 2 has twofold axes on C9 atom. Intramolecular hydrogen bonds occur between O1 and N1 [2.541(3) Å ] and between O3 and N2 [2.573(4) Å ] atoms for 1 and between O1 and N1 [2.631(2) Å ] atoms for 2. The optimized geometries of the crystal structures of 1 and 2 corresponding to non-planar conformation are the most stable conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by non-bonded hydrogen-hydrogen and hydrogen-carbon repulsions.