Haloalkanes …workbook pgs 131 - 132…

Haloalkanes Compound where a halogen (Group 17) replaces one of the hydrogens on a carbon Prepared by substitution reaction of an alkane with a halogen, or by addition reaction of an alkene with HX General Formula: R- X CnH2n+1X `Example: CH3CH(Br)CH2CH2CH3 2-bromopentane

Haloalkane Nomenclature If a Hydrogen is replaced by a halogen, this information is added in the prefix Flourine = “Fluoro-” Chlorine = “chloro-” Bromine = “bromo-” Iodine = “Iodo-” Like alkenes and alkynes, the longest continuous chain must contain the halide. Also, count the carbons so that the halide has the lowest number possible

Types of Haloalkanes Just like with alcohols: 3 Types Primary Haloalkane Haloalkane with only 1 “R” group…. Secondary Haloalkane Haloalkanel with 2 “R” groups… Tertiary Haloalkane Haloalkane with 3“R” groups…

Types of Haloalkanes

Types of Haloalkanes

Properties of Haloalkanes Halide group (except for fluorine) are slightly polar and allows for slightly polar molecules IMF due to temporary dipoles and permanent dipole interactions Haloalkanes have high melting and boiling points than corresponding alkanes Melting and boiling points increase as mass increases Chloromethane, bromomethane, and chloroethane are gases; most other haloalkanes up to 6 carbons are liquids; larger ones are solids Haloalkanes are slightly soluble in water b/c hydrogen bonding can’t occur

Reactions of Haloalkanes Substitution Reactions Nucleophilic substitution – when a nucleophile (negative ion, like OH-, or group with a lone pair of electrons) is attracted to the partially positive carbon atom nearest the halogen atom With Ammonia (NH3) Will form amines

Reactions of Haloalkanes Substitution Reactions Reaction with aqueous hydroxide ion Forms alcohols

Reaction of Haloalkanes Elimination Reaction of Haloalkanes A molecule of HX is removed and an alkene is formed Under non-aqueous strongly basic conditions Opposite of Markovnikov’s rule – H comes off the carbon with the fewest number of H’s attached Primary Haloalkanes very difficult to undergo elimination. Secondary Haloalkanes react faster, Tiertiary the fastest