Halogenoalkanes GapFill

Halogenoalkanes are alkanes in which at least one hydrogen atom has been replaced by a halogen atom. Halogens belong to group  17/1728/18 of the Periodic Table. The first four halogens are fluorine, chlorine,  kryptonarsenicbrominequinine and iodine. For halogenoalkanes with only one halogen atom, the general formula is  CnHnXCnH2n+1XCnH2n+2XCnH2nX, where X is used to represent the halogen atom.

Due to the high electronegativity of most of the halogens, C−X is a  polarmetallichydrogendative bond. One of the most important types of reaction that halogenoalkanes undergo is nucleophilic   isomerisationelectrolysisadditionsubstitution. Nucleophiles are   electron neutralelectron richelectron deficientcarbon neutral, and have a lone pair of   electronsprotonsionscarbon atoms available to form a new covalent bond. Examples of nucleophiles that react with halogenoalkanes include hydroxide (⁻OH), cyanide (⁻CN) and ammonia (  NH3NO2NH4CO). These lead to the formation of alcohols,  ketonesnitrilesazo dyesnitrates and amines, respectively. The mechanism is virtually the same in each case. The nucleophile attacks the carbon atom in the C−X bond, which has a partial positive charge. At the same time, the C−X bond breaks, with both electrons moving to the halogen. The resulting halide ion is called the   departingleavingwithdrawingexiting group. Another important type of reaction is elimination, which forms   alkenesalkanesaminesketones. Here, a base removes a hydrogen atom from one of the carbon atoms next to the C−X bond, forming a double bond and expelling a halide ion.

Chlorofluorocarbons (CFCs) were once used in many industrial applications but have now been banned in most countries because they   destroy the ozone layerare toxicare explosiverequire too much fluorine to make.