Synthesis, characterization, and conformational study of N-acylhydrazone derivatives bearing an indole moiety

Chin, Ker Yin (2026) Synthesis, characterization, and conformational study of N-acylhydrazone derivatives bearing an indole moiety. Final Year Project, UTAR.

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Abstract

A series of N-acylhydrazone derivatives bearing an indole moiety (SB 1 - SB 10) were successfully synthesized, with yields ranging from 67% to 96%. In this project, carboxylic acid hydrazide was used as the starting material for the synthesis of N-acylhydrazones. A total of ten N-acylhydrazones were synthesized through the condensation reactions between the carboxylic acid hydrazide and various benzaldehydes bearing different substituents at different positions. The structures of the carboxylic acid hydrazide and the synthesized N-acylhydrazones were characterized by melting-point analysis and spectroscopic techniques, including FTIR, 1H NMR, 13C NMR, DEPT-135, NOE, HMQC, and HMBC. Based on the relative configuration of the imine (C=N) double bond and the conformation of the amide [C(=O)–NH] bond, the C=N double bonds of the N- acylhydrazones were assigned the E configuration as confirmed by using NOE experiments. The NOE results indicated that all N-acylhydrazones exist as the E geometrical isomer. Furthermore, the ¹H and ¹³C NMR spectra of the synthesized N-acylhydrazones revealed the presence of syn/anti conformers arising from the restricted rotation about the [C(=O)–NH] bond. The proportions of the syn and anti conformers were found in the range of 40% to 68%, respectively, as determined through the integration of the [C(=O)–NH] proton signals in the 1H NMR. Dynamic NMR experiments indicated that the coalescence temperatures (Tc) for the [C(=O)–NH] signals were in the range of K, while the rotational energy barriers of the syn/anti conformers were determined to be between 7 and 77 kJ/mol.

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