Ethyne



CHEMISTRY OF ETHYNE
INTRODUCTION
   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.
Orbital structure of ethyne

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
CHEMICAL PROPERTIES
   COMBUSTION REACTION:
          2C2H2 + 5O2  4CO2 + 2H2O + heat
   ADDITION REACTIONS:
   Addition of Hydrogen:
          C2H2  CH2=CH C2H6
   Addition of Halogen:
          C2H2 +Cl 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
PHYSICAL PROPERTIES
   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.

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