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Updated: May 31, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
(3E,5E)-1-Acryloyl-3,5-bis-(2,4-dichloro-benzyl-idene)piperidin-4-one hemihydrate
Abstract:
The asymmetric unit of the title compound, C(22)H(15)Cl(4)NO(2)·0.5H(2)O, consists of a (3E,5E)-1-acryloyl-3,5-bis-(2,4-dichloro-benzyl-idene)piperidin-4-one mol-ecule and a half-mol-ecule of water (the O atom of the water mol-ecule lies on a twofold axis). The piperidin-4-one ring adopts an envelope conformation. The dihedral angle between the two terminal benzene rings is 8.84 (11)°. In the crystal, mol-ecules are connected by C-H⋯O hydrogen bonds forming supra-molecular chains along the c axis. Furthermore, adjacent chains are inter-connected by the water mol-ecules via O-H⋯O hydrogen bonds.
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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.
Nomenclature of Carboxylic Acid Derivatives: Acid Halides, Esters, and Acid Anhydrides
The IUPAC and common names of acid halides are derived from the corresponding carboxylic acids, by changing “ic acid” to “yl halide.” For example, as shown below, the IUPAC name ethanoyl chloride is derived from ethanoic acid, and the common name, acetyl chloride, is obtained from acetic acid.

