Steric Effects Promoted Intermolecular C—H…O Hydrogen Bonds In Solution

In this thesis, IE (2-(1-imidazolyl) ethanol), IP (L-2(S)-(1-imidazolyl) propanol), IMP (L-2(S)-(1-imidazolyl)-3(S)-methylpentanol) and IPP (L-2(S)-(1-imidazolyl)-3-phenylpropanol) were prepared from glycine, L-alanine, L-isoleucine, L-phenylalanine, respectively. Solvent effects of MI (1-methyl imidazole), IE, IP, IMP, and IPP were investigated using NMR and density functional theory (DFT). The following issuess were approached:(1) ¹H NMR spectra of protons on the imidazole ring of MI, IE, IP, IMP, and IPP were recorded in D₂O and CDCl₃, respectively. Their ¹H chemical shifts (8) of H_a, H_b and H_c on the imidazole ring exhibit different spectral pattern. The distance between H_c and N^I-substituent is great, and so it leads to ¹H chemical shifts for H_c of all substrates in D₂O and CDCl₃ have almost the same values. However, H_a and H_b are near by the N¹-substituent, Their ¹H chemical shifts are affected by the steric effects of the N¹-substituent. ¹H chemical shifts of H_a in D₂O increase with the increasing bulk of N¹-substituent of MI, IE, IP and IMP. ¹H chemical shifts of H_a in CDCl₃ decrease with the increasing bulk of N¹-substituent of MI, IE, IP, IMP and IPP. Meanwhile, the H_b has the similar behavor. The change in ¹H chemical shifts of H_a and H_b (△δ(D₂O -CDCl₃)exp) for all substrates in D₂O and CDCl₃ increases with increasing the bulks of N¹-substituent of MI, IE, IP, IMP, and IPP increasing. By analysing of three-dimensional structures of MI, IE, IP, IMP and IPP (size and form of solute and solvent), it will be concluded that the steric effects promote intermolecular C-H…O hydrogen bonds, which originate in interactions of hydrogen atoms C-H on the imidazole ring with the oxygen of water. For example, the changes in ¹H chemical shift (△δ(D₂O - CDCl₃)exp) of IMP in D₂O and CDCl₃ are mainly produced by the 3-methyl-1-pentanol group (C₂H₅CH(CH₃)-CH-CH₂OH).(2) The global stable conformations of MI, IE, IP, BMP and IPP were obtained by rotating the C-C and / or C-N single bonds using semi-empirical method AM1 and...