Bromo-organic compounds 0 determination

What is optical isomerism What do you look for to determine whether an organic compound exhibits optical isomerism 1-Bromo-1-chloroethane is optically active whereas 1-bromo-2-chloroethane is not optically active. Explain. 

G. J. Stridh. On the Slow Oxidation of Arsenic(llT) Oxide to ArsenidV) Oxide in Aqueous Solution by Elemental Oxygen and its Effect on the Precise Determination of Energies of Combustion of Organic Chloro- and Bromo-compounds. J. Chem. Thermodynamics 1975, 7, 703-705. 

In the Mitsubishi organic halogen measurement system, chloro and bromo compounds in the environment (air, water) are adsorbed in columns tilled with activated carbon and then heated at 900°C in a horizontal combustion tube in an oxygen atmosphere. The hydrogen chloride and hydrogen bromide produeed are introduced into the automatic titration cell and determined coulometrically with silver ions. 

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