Organic Chemistry

45 Reactions

Determination of Haloalkanes: A famous test used to determine if a compound is a
haloalkane is the Beilstein test, in which the compound tested is burned in a loop of copper
wire. The compound will burn green if it is a haloalkane. The numbers of fluorine, chlorine,
bromine and iodine atoms present in each molecule can be determined using the sodium
fusion reaction, in which the compound is subjected to the action of liquid sodium, an
exceptionally strong reducing agent, which causes the formation of sodium halide salts.
Qualitative analysis can be used to discover which halogens were present in the original
compound; quantitative analysis is used to find the quantities.

45.1 Substitution reactions of haloalkanes.

R-X bonds are very commonly used throughout organic chemistry because their polar bonds
make them reasonably reactive. In asubstitution reaction, the halogen (X) is replaced
by another substituent (Y). The alkyl group (R) is not changed.

The ”: ” in a chemical equation represents a pair of unbound electrons.

A general substitution reactionY: + R—X→R—Y + X:

Substitutions involving haloalkanes involve a type of substition calledNucleophilic sub-
stitution, in which the substituent Y is anucleophile. A nucleophile is an electron pair
donor. The nucleophile replaces the halogen, anelectrophile, which becomes aleaving
group. The leaving group is an electron pair acceptor. Nuclephilic substition reactions
are abbreviated as SNreactions.

”Nu” represents a generic nucleophile.

General nucleophilic substitution reactionsNu:-+ R—X→R—Nu + X:-

Nu: + R—X→R—Nu++ X:-

Common Nucleophiles

Reagent Nucleophile Name Product Product name

NaOH/KOH :O-H Hydroxide R—OH Alcohol

NaOR’ :O-R’ Alkoxide R—O—R’ Ether

:S-H Hydrosulfide R—SH Thiol

NH 3 :NH 3 Ammonia R—NH 3 + Alkylammonium

ion