When hydrogen bond tailors molecular packing in non-anisometric molecules. The case study of N-alkyl 1,3-diphenyl-4,5-dihydro-1H-pyrazole-5-carboximidamides

ABSTRACT

In this paper, we report the synthesis of novel liquid crystals (LCs) based on 5-membered pyrazoline heterocycle. The synthesis of pyrazoline derivative was carried out by [3 + 2] 1,3-dipolar cycloaddition reaction of benzaldehyde phenyl hydrazone (1) with acrylonitrile, mediated by chloramine-T as the oxidising agent, followed by addition of hydroxylamine hydrochloride, and subsequently alkylated with various alkyl chains to afforded the title compounds. The LCs properties were investigated using differential scanning calorimetry and polarising optical microscopy. For title compounds with longer alkyl chains, monotropic columnar hexagonal mesophase was characterised by XRD analysis. The mesophase-formation was driven by intermolecular hydrogen bonds despite their non-discoid molecular structure.

GRAPHICAL ABSTRACT

KEYWORDS:

• Pyrazolines
• liquid crystals
• mesophases
• chloramine-T
• hexagonal columnar

Acknowledgments

SYK would like to acknowledge the University of Mysore for providing laboratory facility to carry out this work. AAM and AAV thank MCTI/CNPq Ed. Universal grant numbers 403075/2016-5 and 422750/2018-2 for financial support in instrumental analysis. The XRD experiments were carried out in the Laboratório de Difração de Raios X (LDRX/UFSC).

Disclosure interest

The authors declare no conflict of interest.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the MCTI/CNPq Ed. [403075/2016-5 and 422750/2018-2].