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Organic Halides(Haloalkanes)(Alkyl Halides)
Functional Group #1
Structure
• R-X
where R = alkyl group
and X = halide (F, Cl, Br, I)
bromoethane
Cl |
CH=C-CH2-CH3
| Cl
1,2-dichloro-1-butene
Nomenclature
Fluorine Fluoro-
Chlorine Chloro-
Bromine Bromo-
Iodine Iodo-
Prefixes for the first four members of the halogen family
Prefixes for halides are inserted into the name of the structure in the exact same fashion as any alkyl group. Remember to write them in alphabetical order
Properties
• The presence of a halide makes the molecule more polar.
• Since water is also polar and “like dissolves like”, alkyl halides are soluble in water. The more halides connected to the parent chain, the more polar the molecule.
• The polar nature of the molecule means that boiling and melting points of alkyl halides are much higher than alkanes with a similar number of carbons (see pg. 34 in the text)
Uses
• CFC’s (Chlorofluorocarbons) are used in refrigerators and air conditioners (ex. Freon) (their use is now restricted due to the fact that some of them damage the ozone layer)
• polymers such as Teflon (non-stick surfaces as in cookware) and PVC (polyvinylchloride) used plumbing
• DDT (dichlorodiphenyltrichloroethane) – now banned pesticide
• PCB’s (polychlorinated biphenyls) – electrical transformers
Reactions – Preparing Alkyl Halides• Alkenes/Alkynes readily react with halides of
acids to form alkyl halides.
C=C and C≡ C are weak bonds that are easily broken making molecules that contain them more reactive than alkanes
• Halogenation (by addition)Ex. C2H4 + HCl → C2H5Cl
• Substitution reactions with HalogensEx. benzene + Br → bromobenzene + HBr
Markovnikov’s Rule
• When Alkene or Alkyne reacts with a hydrogen halide or water the H bonds to the Carbon with the most H already attached. The Rich get Richer! See the
Markovnikov’s Rule
Two more examples:
Reactions - Reactions with aromatics
Substitution
FeCl3 catalyst
C6H6 + Cl2 ===========> C6H5Cl + HCl chlorobenzene
