Synthesis, crystal structure, optical, electrochemical and thermal properties of the ynamide: Bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide

• The novel ynamide 3, having a 1,3-butadiyne-1,4-diamide moiety was prepared.
• First characterization of a 1,3-butadiyne-1,4-diamide by X-ray diffraction.
• The helical twisted molecular structure of diynamide 3 implies helical twisted MOs.
• The HOMO–LUMO energies of 3 were determined by optical and electrochemical methods.
• Probable topochemical ynamide polymerization was investigated.

The novel ynamide compound, bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3), was synthesized and characterized by single crystal X-ray diffraction, 1H and 13C NMR, UV-fluorescence spectroscopy, cyclic voltammetry, TGA and DSC techniques. This first reported X-ray structure of a 1,3-butadiyne-1,4-diamide revealed that the amido substituents of 3 adopt a twisted conformation in the crystal with a torsion angle of 76.6° resulting in a molecule with axial chirality. The crystal structure of compound 3 is stabilized by intermolecular CH-π interactions that give pairs of stacked bis-alkyne-3 units. HOMO/LUMO energy levels of 3 were experimentally determined by means of electrochemical and optical methods to be −5.87/−1.98 eV respectively. The solid state polymerization of the title compound was investigated by differential scanning calorimetry (DSC) revealing that polymerization proceeded simultaneously to the phase transition assigned to the melting of 3. The solid state polymerization of 3 is discussed of being a topochemically initiated polymer chain reaction that proceeds with a non-topochemical chain growth.

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