!1!Chapter!4:!Alcohols!and!Alkyl!Halides!• 4.18!Functional!Groups!o Major!Classes!of!Organic!Compounds!Class!Generalized!Abbreviation!Alcohol!8OH!Alkyl!halide!8X!(halogen)!Amine!8NH2!Epoxide!!Ether!8O8!Nitrile!8C!!!N!Nitroalkane!8NO2!Sulfide!8S8!Thiol!8SH!Aldehyde!O!ll!8CH!Ketone!O!ll!8C8!Carboxylic!Acid!!Acyl!halide!O!ll!8CX!Acid!anhydride!!Ester!O!ll!8CO8!Amide!O!ll!8CN8!o Alcohols!resemble!water!in!their!acidity!o Carboxylic!acid!is!a!weak!acid!but!st ronger!acid!than!alcohol! Carbonyl8containing!(C==O)!compounds!rank!among!the!most!abundant!and!biologically!significant!classes!of!naturally!occurring!substances!• 4.28!IUPAC!Nomenclature!of!Alkyl!Halides!!2!o Functional!class!nomenclature:!the!alkyl!group!and!the!halide!are!designated!as!seperate!words!o The!alkyl!group!is!named!bases!of!its!longest!continuous!chain!beginning!at!the!carbon!to!which!the!halogen!is!attached! CH3F!!methyl!fluoride! CH3CH2CH2CH2CH2Cl!!pentyl!chloride! !!cyclohexyl!iodide!o Substitutive!nomenclature:!treats!the!halogen!as!a!halo!substituent!on!an!alkane!chain.!! The!carbon!chain!is!numbered!in!the!direction!that!gives!the!substituted!carbon!the!lower!number! Is!listed!alphabetically!• CH3CH2CH2CH2CH2F!!18fluoropentane!• 4.38!IUPAC!Nomenclature!of!Alcohols!o The!alkyl!group!that!bears!the!hydroxyl!substituent!(8OH)!and!then!adding!alcohol!as!a!separate!word!o Substitutive!names!of!alcohols!are!developed!by!identifying!the!longest!continuous!chain!that!bears!the!hydroxyl!group!and!replacing!the!–e!ending!of!the!corresponding!alkane!by!the!suffix!–ol! CH3CH2OH!!ethyl!alcohol!or!ethanol! !!trans828methylcyclopentanol!• 4.48!Classes!of!Alcohols!and!Alkyl!Halides!o Alcohols!and!alkyl!halides!are!classified!as!primary,!secondary,!and!tertiary!according!to!the!degree!of!substitution!of!the!carbon!that!bears!the!functional!group!o Where!these!functional!groups!are!placed!determine!what!the!properties!of!the!alcohols!are!o Halogens!and!oxygen!are!more!electronegative!than!carbon,!and!the!carbon8halogen!bond!in!alkyl!halides!and!the!carbon8oxygen!bond!in!alcohols!are!polar!• 4.58!Bonding!in!Alcohols!and!Alkyl!Halides!o The!carbon!that!bears!the!functional!group!is!sp38!hybridization!on!in!alcohols!and!alkyl!halides! The!halogen!connected!to!sp38!hybridization!carbon!by!a!σ!bond.!C—F!<!C—Cl!<!C—Br!<!C—I!! Carbon8oxygen!and!carbon!halogen!bonds!are!polar!covalent!bonds!and!carbon!bears!a!partial!positive!change!in!alcohols!and!in!alkyl!halides! Polar!molecules!!!!3!• 4.68!Physical!Properties!of!Alcohols!and!Alkyl!Halides:!!Intermolecular!Forces!o Boiling!Point! Dipole8dipole!attractive!force.!Two!molecules!of!a!polar!substance!experience!a!mutual!attractive!between!the!positively!polarized!region!of!one!molecules!and!the!negatively!polarized!region!of!the!other!! Permanent!dipoles!have!stronger!intermolecular!forces!than!alkanes! Intermolecular!forces!importance!can!be!seen!by!shape!and!size!! The!attractive!forces!in!ethanol!are!usually!strong! Hydrogen!bonding!–!15820!times!weaker!than!covalent!bonds;!organic!compounds!that!involve!hydrogen!bonding!are!oxygen!and!nitrogen!• The!hydrogen!must!be!bonded!to!a!strongly!electronegative!element!in!order!for!the!bond!to!be!polar!enough!to!support!hydrogen!bonding!• Among!alkyl!halides,!the!boiling!point!increases!wit!increasing!size!of!the!halogen!• In!–OH,!oxygen!is!the!hydrogen!bond!acceptor!and!the!hydrogen!is!the!hydrogen!bond!donor! Polarizablility!• Induced8dipole/induced8dipole!attractions!are!strongest!in!alkyl!iodides,!weakest!in!alkyl! fl uorides!• Chloromethane:!824°C!Dichloromethane:!40°C!Trichloromethane:!61°C!Tetrachloromethane:!77°C! Increasing!the!number!of!halogens!also!increases!the!induced!dipole8induced!dipole!attractive!forces!and!therefore!the!boiling!point!o Solubility!in!Water! All!alkyl!halides!are!insoluble!in!water! Low8molecular!weight!alcohols!are!soluble!in!water!o Density! Alkyl!fluorides!and!chlorides!are!less!dense,!and!alkyl!bromides!and!iodides!more!dense!than!water! When!the!alkyl!halide!is!a!fluoride!or!chloride,!it!is!the!upper!layer!and!water!is!the!lower! Alkyl!halide!is!a!bromide!or!an!iodide.!In!these!cases!the!alkyl!halide!is!the!lower!layer! Liquid!alcohols!have!densities!of!approximately!0.8!g/mL!and!are,!therefore,!less!dense!than!water! Increasing!halogenation!increases!density!• 4.7!–!Preparation!of!Alkyl!Halides!from!Alcohol!and!Hydrogen!Halides!!4!o The!reaction!of!alcohols!with!hydrogen!halides!yields!alkyl!halides!o R—OH!+!H—X!!R—X!+!H—OH!o The!order!of!reactivity!of!the!hydrogen!halides!parallel!their!acidity! HI!>!HBr!>!HCl!>!HF!o Tertiary!alcohols!are!observed!to!be!the!most!reactive!and!primary!alcohols!the!least!reactive! Tertiary!needs!low!temperature!and!primary!need!a!high!temperature! Tertiary!alcohols!are!converted!to!alkyl!chlorides!• (CH3)3COH!+!HCl!!(CH3)3CCl!+!H2O! Secondary!and!primary!alcohols!do!not!react!with!HCl!at!rates!fast!enough!to!make!the!preparation!of!the!corresponding!alkyl!chlorides!a!method!of!practical!value!• !!+!HBr!! ! !!+!H2O!• 4.8!–!Mechanism!of!the!Reaction!of!Alcohols!with!Hydrogen!Halides:!Hammond’s!Postulate!(the!SN1!mechanism)!o The!reaction!of!an!alcohol!with!a!hydrogen!halide!is!a!substitution!o The!mechanism!is!the!step8by8step!pathway!of!bond!cleavage!and!bond!formation!that!leads!from!reactants!to!products!o Hammond’s!postulate:!if!two!states!are!similar!in!energy,!they!are!similar!in!structure!o A!halogen!replaces!a!hydroxyl!group!as!a!substitution!on!the!carbon!o An!elementary!step!is!one!that!involves!only!one!transition!state!o Step!1:!Protonation!(exothermic)! ! Proton!transfer! The!alcohol!act!as!a!Brønsted!base! Proton!transfer!to!an!alcohol!gives!an!alkylozonium!ion!(ROH2+)! In!all!reactions,!the!first!step!gives!us!a!alkylozonium!ion!!5! Potential!Energy!Diagram!! The!transition!state!is!not!a!stable!structure!and!the!bonds!are!partially!formed!and!broken!o Step!2:!dissociation! ! Carbocation!Formation!–!high!energy!(sp2)! The!alkyloconium!ion!dissociates!to!a!molecule!of!water!and!carbocation!(an!ion!that!contains!a!positively!charge!carbon)! Because!this!step!is!endothermic,!the!products!of!it!are!placed!higher!in!energy!than!the!reactants!