1. Organic Halides (Haloalkanes) (Alkyl Halides)
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Functional Group #1

2. Structure bromoethane R-X where R = alkyl group
and X = halide (F, Cl, Br, I)
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     Cl                    |            CH=C-CH2-CH3 |                     Cl                   
1,2-dichloro-1-butene
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bromoethane

3. Prefixes for the first four members of the halogen family
Nomenclature
Fluorine
Fluoro-
Chlorine
Chloro-
Bromine
Bromo-
Iodine
Iodo-
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
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Prefixes for the first four members of the halogen family
Dr Seemal jelani Chem-261

4. 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
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Dr Seemal jelani Chem-261

5. 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
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Dr Seemal jelani Chem-261

6. 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 Halogens
Ex. benzene + Br → bromobenzene + HBr
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Dr Seemal jelani Chem-261

7. 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
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Dr Seemal jelani Chem-261

8. Markovnikov’s Rule Two more examples: 9/16/2018
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9. Reactions - Reactions with aromatics
Substitution
FeCl3 catalyst
C6H6 + Cl2 ===========> C6H5Cl + HCl Chlorobenzene
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10. Preparation of Alkyl Halides from Alcohols
Alkyl halides can be prepared from alcohols by reaction with HX, i.e., the substitution of a halide on a protonated alcohol.
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Rapid. 3° C+ is stabilized by protic solvent (H2O)
Dr Seemal jelani Chem-261

11. Very slow. Protic solvent inhibits the nucleophile
OH- is a poor leaving group, i.e., is not displaced directly by nucleophiles. Reaction in acid media protonates the OH group producing a better leaving group (H2O). 2 and 3 alcohols react by SN1 but Me° and 1 alcohols react by SN2.
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Dr Seemal jelani Chem-261 .

12. Preparation of Alkyl Halides from Alcohols
Alternative to using hydrohalic acids (HCl, HBr, HI), alcohols can be converted to alkyl halides by reaction with PBr3 which transforms OH- into a better leaving group allowing substitution (SN2) to occur without rearrangement.
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Dr Seemal jelani Chem-261

13. Preparation of Alkenes from Alkyl Halides
2° and 3° alkyl halides can be dehydrohalogenated with a strong base such as OH- producing an alkene.
Bromocyclohexane KOH  cyclohexene (80 % yield)
Clearly, this is an E2 reaction.
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Dr Seemal jelani Chem-261

14. Summary of SN /Elimination Reactions
Alkyl Halide Substrate Reactivity:
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Dr Seemal jelani Chem-261

15. Reactivity of Nucleophiles
Leaving Group Activity
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16. Note
Poor nucleophiles that are also weak bases (H2O, ROH, CH3COOH, etc.) do not undergo any reaction unless a C+ is formed first
If a C+ can form (as with a 2º, 3º, any benzylic, or any allylic halides), then E1 and SN1 generally occur together.
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Dr Seemal jelani Chem-261