Molecular formula = C2H2 Empirical formula = CH Molecular mass = 26 Empirical mass = 13 Common name = Acetylene Homologous series = Alkynes
ORBITAL STRUCTURE OF ETHYNE
COMPOSITION OF ETHYNE MOLECULE: Ethyne molecule consists of two C-atoms and two H-atoms (C2H2). NATURE OF HYBRIDIZATION: In ethyne molecule, each carbon atom is Sp-hybridized. Due to Sp-hybridization, each carbon atom generates two Sp-hybrid orbitals. In this way there exists four Sp-orbital in ethyne. These Sp-orbital are arranged in linear geometry and 180o apart. Remaining py and pz unhybrid orbitals of each carbon atom lie perpendicular to the plane of Sp-orbitals. SIGMA BOND FORMATION: One Sp-hybrid orbital of each carbon atom overlaps to produce one sigma bond between two C-atoms.The remaining one Sp-orbital of each C-atom overlaps with one H-atom to produce sigma bond. Pi-BOND FORMATION: Py and Pz orbital of two carbon atoms are un-hybrid and make parallel overlapping to produce pi-bond. BOND LENGTH: The C–H bond is 1.09A and C-C is 1.2A.o. BOND ANGLE: HCC bond angle is 180o.
METHODS OF PREPARATION
BY THE HYDROLYSIS OF CALCIUM CARBIDE: CaC2 + 2H2O C2H2 + Ca(OH)2 BY TETRA CHLOROETHANE: Cl2CH-CHCl2 + 2Zn C2H2 + 2ZnCl2 BY 1,2-DIBROMOETHANE: Br-CH2-CH2-Br + KOH C2H2 + 2KBr + 2H2O
-COMBUSTION REACTION: 2C2H2 + 5O2 4CO2 + 2H2O + heat -ADDITION REACTIONS: Addition of Hydrogen: C2H2 CH2=CH2 C2H6 Addition of Halogen: C2H2 +Cl2 Cl-CH=CH-Cl Cl2CH-CHCl2 Addition of Hydrogen Halide: C2H2 + HBr CH2=CH-Br + HBr CH3-CHBr2 Addition of HCN: C2H2 + HCN CN-CH=CH-CN Addition of Water: C2H2 + HOH CH2=CH-OH [rearrangement] CH3CHO (Ethanal) Oxidation of Ethyne: In cold solution C2H2 + HOH + 3[O] 2HCOOH (Formic acid) In hot solution, C2H2 +4[O] (COOH)2 (Oxalic acid) -SUBSTITUTION REACTIONS: CONSULT YOUR TEXT BOOK
-Ethyne is a colourless gas with a characteristic smell. -It has a melting point -81oC. -It has a boiling point -84oC. -It is significantly soluble in water. However, readily soluble in organic solvents.
USES OF ETHYNE
-It is used in welding to produce oxy-acetylene flame of temperature about 3000oC. -It is used in the synthesis of useful compounds such as ethanol, ethanoic acid, PVC, acetaldehyde.