1 / 11

Organic chemistry for medicine and biology students Chem 2311 Chapter 6

Organic chemistry for medicine and biology students Chem 2311 Chapter 6 Alkylhalides (Substitution and Elimination) By Prof. Dr. Adel M. Awadallah Islamic University of Gaza. Alkyl Halides (Substitution and Elimination)

Olivia
Télécharger la présentation

Organic chemistry for medicine and biology students Chem 2311 Chapter 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Organic chemistry for medicine and biology students Chem 2311 Chapter 6 Alkylhalides (Substitution and Elimination) By Prof. Dr. Adel M. Awadallah Islamic University of Gaza

  2. Alkyl Halides (Substitution and Elimination) • alkyl halides = Halogenoalkanes = haloalkanes contain a halogen atom - fluorine, chlorine, bromine or iodine - attached to an alkyl • The different kinds of halogenoalkanes • Primary (1°) includes CH3Br • Secondary (2°) Tertiary (3°)

  3. The polarity of the carbon-halogen bonds • Electro negativity values (Pauling scale) • C = 2.5, F = 4.0, Cl = 3.0, Br = 2.8, I = 2.5 • Strengths of various bonds (all values in kJ mol-1). • C-H = 413 • C-F = 467 (very polar, but very strong and difficult to break) • C-Cl = 346 • C-Br = 290 • C-I = 228 (non polar, but it is polarized in the reaction by any nucleophile) Rates of reaction: RCl < RBr < RI

  4. Nucleophilic substitution in primary alkyl halides • NucleophilesA nucleophile is a species (an ion or a molecule) which is strongly attracted to a region of positive charge in something else. • Nucleophiles are either fully negative ions, or else have a strongly - charge somewhere on a molecule. Common nucleophiles are hydroxide ions, cyanide ions, water and ammonia. • Notice that each of these contains at least one lone pair of electrons, either on an atom carrying a full negative charge, or on a very electronegative atom carrying a substantial - charge.

  5. Strength of nucleophiles • A) Charged nucleophiles are stronger than neutral ones • OH- > H2O , EtO- > EtOH, NH2- > NH3 • B) Nucleophile strength increases by going to the left in a period, or down in a group of the periodic table • NH3 > H2O, NH2- > OH- (period) • H2S > H2O, SH- > OH- (group)

  6. Elimination Reactions • Elimination (dehydrohalogenation) reactions of alkyl halides • A hydrogen atom and a halogen atom from adjacent carbons are eliminated and a carbon –carbon double bond is formed • Competition between substitution and elimination

  7. Elimination from unsymmetrical alkylhalides

  8. Polyhalogenated aliphatic compounds • CH3Br (methyl bromide) • Methyl Bromide is a highly effective fumigant used to. control a number of pests including insects • CH2Cl2 (dicholromethane or methylene chloride) • solvent • CHCl3 (Chloroform) • Solvent and was used as an anesthetic • (CF2-CF2)n Teflon • Chloroflouorocarbons (CFC) • CCl2F2 (Freon 12, CFC – 12) refrigerating gas

  9. Halons • Bromine containing CFCsare called halons, and used to extinguish fire • CBrClF2 (Halon–1211) • CBrF3 (Halon-1301)

More Related