Haloalkanes I wonder what these are…”halo”… might be referring to halogens… alkanes… might mean alkanes ;)

Haloalkanes Compound where a halogen (Group 17) replaces one of the hydrogens on a carbon General Formula: – R- X `Example: – CH 3 CH(Br)CH 2 CH 2 CH 3 – 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

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 – Reaction with aqueous hydroxide ion Forms alcohols

Reactions of Haloalkanes Substitution Reactions – With Ammonia (NH 3 ) Will form amines

Reaction of Haloalkanes Test for Haloalkanes – Shake haloalkane with excess NaOH. – Neutralise the excess NaOH with some HNO 3. – Add some AgNO 3 – silver halides are insolube and will precipitates

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