halogenoalkanes or alkyl halides

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Halogenoalkanes or alkyl halides. Sites:. http://brakkeibchem.wikispaces.com/file/view/T10D08+-+10.28.11+-+10.5-6+Halogenalkanes+Sn1+Sn2.pdf Animation: http://www.rod.beavon.clara.net/SN2.htm. Halogenoalkanes contain F, Cl, Br, I bonded to an alkyl group. - PowerPoint PPT Presentation

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  • HALOGENOALKANES

    OR ALKYL HALIDES

  • SITES:http://brakkeibchem.wikispaces.com/file/view/T10D08+-+10.28.11+-+10.5-6+Halogenalkanes+Sn1+Sn2.pdf

    Animation:http://www.rod.beavon.clara.net/SN2.htm

  • Halogenoalkanes contain F, Cl, Br, I bonded to an alkyl group.

    CH3CH2F CH3CH2Cl CH3CH2Br CH3CH2I

    Bond C-F C-Cl C-Br C-I

    Bond Enthalpy 484 338 276 238(kJmol-1 )

  • PRIMARY,SECONDARY,TERTIARY HALOGENOALKANES Primary halogenoalkanes:

    In a primary halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.

  • Secondary:

    Tertiary:

  • HALOGENOALKANES UNDERGO SUBSTITUTION.

    NUCLEOPHILIC SUBSTITUTION

  • NUCLEOPHILEA 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 have a lone pair of electrons. Common nucleophiles are hydroxide ions, cyanide ions, water and ammonia.

  • SUBSTITUTION NUCLEOPHILIC BIMOLECULAR SN2Primary halogenoalkanes undergo SN2:

    Because the mechanism of the reaction involves 2 species, it is known as an SN2 reaction.http://iverson.cm.utexas.edu/courses/310N/ReactMoviesFl05%20/SN2text.html

  • PAGE 226

  • HYDROXIDE ION WITH BROMOETHANE SN2 Mechanismethanolreaction equation2(species reacting in the slowest step)SN2S (substitution)N(nucleophilic)

  • SN1 SUBSTITUTION NUCLEOPHILIC UNIMOLECULAR(CH3)3CBr + OH- => (CH3)3COH + Br-

    2 bromo 2 methylpropane reacts with warm dilute aqueous sodium hydroxide solution to form the tertiary alcohol.

    The rate of reaction shows that the rate depends only on the concentration of the halogenoalkane and does not depend on the concentration of OH-

  • GENERAL RULEPrimary and secondary halogenoalkanes tend to undergo SN2 reactions

    Tertiary halogenoalkanes tend to undergo SN1 reactions

    SN2 reactivity rates follow the trend: CH3X > primary > secondary > tertiary

    Why???? PAGE 227

  • STABILITY OF CATIONS

  • Alkyl groups tend to push the bonding pair of electrons towards the carbon they are bonded to.

    This is known as the positive inductive effect.

    The positive charge can be spread over more atoms, increasing the stability of the ion. It will more likely be formed.

  • SN1 X SN2

  • DIAGRAM OF COMMON ORGANIC REACTIONS.*

  • ANSWERS

  • NUCLEOPHILIC SUBSTITUTIONpropanenitrileCH3CH2I (ethanol)+ CN-(aq)CH3CH2CN + I-cyanide ion with iodoethanecyanide ion with 2-bromo,2-methylpropane2,2-dimethylpropanenitrile(CH3)3CBr (ethanol) + CN-(CH3)3CCN + Br-(aqueous)mechanism

  • CN- ION WITH 2-BROMO,2-METHYLPROPANE (SN1)Nucleophilic substitution mechanism2,2-dimethyl propanenitrile1(species reacting in the slowest step)SN1S (substitution)N(nucleophilic)reaction equation

  • ELIMINATION

  • PRINCIPLES OF ELIMINATIONElimination of a hydrogen halide produces an alkene

    In general, in aqueous solution substitution takes place

    In ethanolic solution, elimination takes place

  • MECHANISMSE1

    E2

    The particular mechanism depends on the strength of the base and the environment of the halide atom

  • E2

  • E1

    The bond is very strong because the atom is small and fluorocarbons are used as fire extinguishers**Odd one out?1 = James Young Simpson2 = deodorant3 = ozone layer4 = pesticide(c) (i)A. = CH3(CH2)7CHO;B. = CH3(CH2)7COOH / CH3(CH2)7CO2H;C. = (CH3)3COH;D. = (CH3)2CO;E. = BrCH2CH2Br; [5]Allow correct structural formulas.*