2-[(E)-4-(Diethyl-amino)-styr-yl]-1-methyl-pyridinium iodide
Abstract:
In the title compound, C(18)H(23)N(2) (+)·I(-), the cation exists in the E configuration with respect to the ethenyl C=C bond. The pyridinium and benzene rings are nearly coplanar, making a dihedral angle of 4.63 (7)°. The two ethyl groups of the diethyl-amino substituent point in opposite directions with respect to the benzene plane. In the crystal, the cation and the iodide anion are linked by a weak C-H⋯I inter-action. The cations are stacked in an anti-parallel manner along the a axis by a π-π inter-action with a centroid-centroid distance of 3.5262 (9) Å. The crystal structure is further stabilized by C-H⋯π inter-actions.
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Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.


