Study of substituent effects on intramolecular hydrogen bonding of (5Z)-7-[(1R,2R,3S,5S)-2-(4-substituted benzoylamino)-6,6-dimethylbicyclo[3.3.1] hept-3-yl] hept-5-enoic acids and their esters in dilute CCl_4 solution by FTIR spectroscopy

摘要

FTIR spectra of the title carboxylic acids I-A-I-E with five p-substituents [N(CH_3)_2,OCH_3,H,CF_3,NO_2] and their esters II-A-II-E were measured in dilute CCl_4 solution. These spectra were subjected to curve analysis to separate overlapping absorption bands. For I-A-I-E, three kinds of intramolecular hydrogen bonds H_1, H_2 and H_3 involving large rings of more than 11 members were found between the C = O bond of the carboxyl group and the NH bond of the p-substituted benzoylamino group and between the OH bond of the former gorup and the C = O bond or the pi-electrons in the benzene ring of the latter group, respectively. The respectively percentages h_1, h_2 and h_3 of molecules forming these hydrogen bonds H_1, H_2 and H_3 in I-A-I-E were determined. The percentage h_1' of the H_1 type of hydrogen-bonded molecules in II-A-II-E was also determined. The substituent effects on these percentages of I-A-II-E were investigated because three kinds of conformations with the large-membered rings formed by these hydrogen bonds coexist in equilibrium. In order to consider the experimental results theoretically, MNDO calculations were carried out for p-substituted N-methyl-benzamides.