!!CHM!2201! Fall!2010! Department!of!Chemistry!Organic!Chemistry!Lab!I! ! Villanova! University Page 1 of 13 !"#$%&%' )* +," )-" .*/"01/#$ .*2"/ 3&) #%2 )-" 4#,&0, *5 6,*7"$&,7 If!you!haven't!already!done!so,!buy!a!"Molecular!Visions"!molecular!model!kit!from!the!stockroom.!It!is!the!kit!that!comes!in!the!green!plastic!box.!Here!is!what!we'll!cover!in!today's!lab:!1) 8-" 9*77*% :%2 ;*< =/"7"%) >$","%)#)&*%, ?@@ ABCAA *5 )-" 7*2"/ D&) 7#%1#/E With!the!he lp!of! your!prof essor!and!TA's,!together!we!are!going!to!go! thro ugh!some! of!the!contents! of!your!kit.!!We! will!follow! what! is!on!pages!10‐11! of!the!manual!that!came!with!your!kit.!Note:!try!to!learn!which!pieces!are!needed!to!make!organic!compounds;!also!note!how!to!put!all!the! pieces!bac k!in!the!box!as!it!is!a!tight!fi t!and!every!piece!has!a!particular!place!!!2) F,,"7G/H #%2 I&,#,,"7G/H *5 F)*7, JK&)- 4*%2,J ?@@ ALCAME Carefully! follow! the! descriptions! on! making! an!sp#$hybridized! atom,! and! making!atoms!joined!by!a!do uble!bond.!!It!is!important!to!learn!how!to!put!thes e!pieces!together!properly!and!securely,!and!learn!how!to!take!them!apart!efficiently.!!NE 9*%,)$10)&%' # O#$&")H *5 7*/"01/", We'll! begin!by!keeping!things!simple:!!!putting!tog ether!molecules!containing!only!carbon!and!hydrogen,!frequently!called!!"#$%&'$(%)*%$And! we'll! start! off! with! sat(rated$ acyclic! hydrocarbons.! ! What! does! this! mean?!!Saturated!means!all!the!carbons!are!sp+$hybridized!(or!maybe!a!better!way!to!think!of!it!is!that!the!molecule! is! saturated! with! hydrogens,! thus! all! carbon‐! carbon! bonds! present! are! single! bonds).!Acyclic! means! "non‐cyclic",!meaning! there! are! no!rings!of! carbon!atoms! present,! which! says!that!from!any!carbon!atom!in!the!molecule,!you!cannot!traverse!along!the!carbon!chain!and!get!back!to!the!same!carbon!you!started!from.!!!CHM!2201! Fall!2010! Department!of!Chemistry!Organic!Chemistry!Lab!I! ! Villanova! University Page 2 of 13 =P"$0&," QA Try! pu tting! together! these! molecules! with! your ! models,! given! the! molecular!formula!(name!in!parentheses):!9RS ?7")-#%"E 9:RT ?")-#%"E 9NRU ?@$*@#%"E Note!how! three‐dimensional! these! systems! are,! and!how!many!different! shapes! (what!organic! chemists! call! conformations$ or! conformers2$ the! latter! is! short! for! 'conformational!isomers')!that!ethane!and!propane!can!have.!!Various!conformers!of!a!hydrocarbon!are!obtained!by!rotating !about!the!C―C !single!bonds.!You!will!learn!from!lecture!that!there!is!usually!considered!to!be!"free!rotation"!about!C―C!single!bonds.!!Note!that!free$rotatio n$is!in!quotes.!!That!is!because!there!are!barriers!to!the! rotation! about! C―C! single! bonds,! but! these! barriers! are! usually! very! small! and! the!thermal!energy!present!at!ambient! conditions!(i.e.!~20!°C)!is!sufficient!that!the!barriers!are!easily!traversed.!Question #1: What!is!the!general!formula!for!a!saturated!acyclic!hydrocarbon?! =P"$0&," Q: Now!put!together!a!molecule!with!molecular!formula!9SRAB.! You!probably!put!together!this!one,!didn't!you?!!9RN9R:9R:9RN !The! molecule! above! is! known! as! n‐butane! (where! the! 3n3$ s tands! for! normal,!meaning!somehow!it!is!'normal'!in!organic!chemistry!when!all!the! carbons!in!a!molecule!are!bonded! together! one! after! the! other,! in! one! continuous! chain).! ! Note! that! n‐butane! is! also!commonly! written! on! paper! as! the! following! car5on$ s6eletal$ diagram$ (also! called! a! 5ond8line$form(las9:$!!CHM!2201! Fall!2010! Department!of!Chemistry!Organic!Chemistry!Lab!I! ! Villanova! University Page 3 of 13 Note!that!in!this!notation!a!carbon!atom!is!implied!at!the!end!of!each!line!(unless!some!other!atom!is!explicitly!written),!and!that!none!of!the!hydrogens!are! drawn.!!In!this!type!of!drawing,!the!only!atoms! explicitly! shown! are! those! that! are! not! carbon! or! a! hydrogen! bonded! to! carbons! (but!hydrogens!bonded!to!other!atoms!like!N!or!O!are!shown).!!Maybe!some!of!you!put!together!this!one!for!9SRAB:! This!structure!is!also!a!9SRAB,!but!it!is!not!the!same!as!n‐butane.!This!9SRAB!is!called! isobutane!(or! 2‐methylpropane!using! the! IUPAC!systematic! nomenclature).!Since!it!has! the!same!molecular!formula!as!n‐butane,! but! it! is!a!different! compound,! they! are! isomers.! ;‐butane!and!isobutane!are!more!accurately!called!&%)*,-,.,-%)'/ -*%12$*$because!the!atoms!in!each!are!bonded!in!a!different!order.!=P"$0&," QN As!the! molecular!formula!becomes! larger,!the! number!of! isomers! rises! rapidly.! As! an!exercise,!put!together!all!the!isomers!of!formula!9LRA:.!You!should!come!up!with!three!total.!Now!that!you!know!a!bit!about!bond‐line!drawings!and!what!they!mean,!put!together!a!model!corresponding!to!the!following!bond‐line!formula:! This!five‐carbon!molecule!is!cyclic!and!is!known!as!cyclopentane.! Question #2: What! is! the! molecular! formula! of! cyclopentane?! ! Does! it! fit! the! general!formula! you! derived! for! saturated! acyclic! hydrocarbons?! ! If! not,! derive! a! general! formula! for! a!saturated!monocyclic!(one!ring)!hydrocarbon.!!!CHM!2201! Fall!2010! Department!of!Chemistry!Organic!Chemistry!Lab!I! ! Villanova! University Page 4 of 13 Note:!although!it!is!easiest!to!write!cyclopentane! on!paper!as!a!simple! pentagon,!this!drawing!doesn't!represent!well!the!three‐dimensional!shape!of!the!molecule.!!Play!around!with!the!cyclopentane! molecule! to! see! if! you! can! guess! what! might! be! the! preferred! shape! (i.e.!conformation).!=P"$0&," QS Now!put!together!the!one!carbon!larger!saturated!cyclic!hydrocarbon,!known!as!cyclohexane:!! Notice!how!difficult! it!is!to!get!this!structure!in!the!shape!of!a!regular!hexagon!with!all!carbons!in!the! same! plane.!! Here!we! again!demonstrate!the!three‐dimensional!nature!of!organic !molecules!and!why!they!can!be!difficult!to!represent!on!a!two‐dimensional!piece!of!paper!!After! playing! around! with! cyclohexane! you! may! have! discovered! that! the! preferred!conformation!for!cyclohexane!is!commonly!called!the!"chair"!form,!as!it!somewhat!resembles!the!shape!of!a!reclining! chair.!!An!attempt!to!draw!this!on!paper!using!a!bond‐line!formula!looks!like!the!following:! Note!that!the!twelve!hydrogens!in!the! planar!conformation!of!cyclohexane!are!equivalent,!but!in!the! preferred! chair! conformation! they! are! not,! with! there! being! two! sets! of! 6!