Organic chemistry exam helper introduction to organic chemistry

OrganicChemistryExamHelper
IntroductiontoOrganicChemistry

ByMatthewPasek,Ph.D.


OrganicChemistryExamHelper:IntroductiontoOrganicChemistryby
MatthewPasek
PublishedbyFreeRadicalConsulting
2703PembertonCreekDrive,SeffnerFL33584

©2017MatthewPasek

Allrightsreserved.Noportionofthisbookmaybereproducedinanyform
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Forward
Thisbookispartofaseriesoforganicchemistrystudyguides.Itfocusesonthe
introductorymaterialcoveredbyorganicchemistryclasses:ageneraloverview,
detailsofbonding,molecularformulae,acidsandbases,hybridization,
nomenclature,andconformations.Mostimportanttothestudentoforganic
chemistryarethequizzesattheend.Thesequizzesallowyoutotestyour
knowledgeofkeyconcepts.Withorganicchemistry,practicemakesperfect.
Thefrequentpracticeoforganicchemistryreactionswillhelpyoupass,oreven

ace,anorganicchemistryexam.

Thesubjectscoveredinthisbookaretheintroductorymaterialsoforganic
chemistry.Eachorganicchemistryclassisdifferent:somewillemphasize
specificcharacteristicsnotincludedhere,otherswillbesticklersforcertain
aspectsoforganicchemistry(typicallyifthat’stheprofessor’sareaoffocus)and
maynotusethesamesuiteasthoseshownhere,andstillotherswillfocusona
bareminimumsetofconcepts,dueeithertotimeconstraintsorpedagogical
concerns.Thisguideismeanttosupplement,andnotreplace,attendingthe
organicchemistrycourse.

Iamaprofessorofgeochemistryandnotanorganicchemist.However,the
organicchemistryfundamentalsareanimportantpartofanychemist’straining,
andIlearnedorganicchemistryleftandrightformyownresearchandformy
grants.I’vetutoredmanystudentsinthissubject,butitispossibleforthereto
beerrorsinthesequestionsasIamnotanorganicchemistbyprofession.

FigureshereweredrawnusingACDlab’sChemSketchprogram.Thisprogram
isgreatfordrawingorganicmolecules.Othersketchesaredonebyhandorwith
powerpoint.


TOC

Contents
1.Whatisorganicchemistry?
2.Bondsinorganicchemistry
3.Molecularformula
4.SaturationChemistry
5.Resonance

6.Skeletaldrawings
7.Molecularhybridization
8.AcidsandBases
9.From2Dto3D
10.Isomers
11.Stereoisomers
12.MolecularAttractiveForces
13.HydrogenBonding
14.Nomenclature
15.Nomenclature2
16.Fromdiagramstonomenclature
17.QuizMe!
18.ConclusionandCartoon




1.Whatisorganicchemistry?

Chemistryisthescienceoftheelectron.Organicchemistryisabranchof
chemistry.Organicchemistryisthechemistryoftheelementcarbon,gliblyput.
Nearlyall(butNOTall)carboncompoundsareorganiccompounds.Organic
chemistryaroseoutofasearchforadifferencebetween“alive”and“notalive”.
Suchasearchinvolvedaconceptcalled“vitalism”,thebeliefthattherewas
somethingfundamentallydifferentbetweenthemoleculesoflifeandthosethat
wereformedbynon-life.Well,itturnsoutthereisn’treallyanymajor
difference.Asidefromabitmoreradiocarboninlivingthings(becausethey
activelyexchangecarbonwiththeatmosphere,unlikemostnon-living
reactions),thechemistryoforganiccompoundsmadebylifeorbymanandnonbiologicreactionsisthesame.Fundamentally,thechemistryofnon-living
carboncompoundsisidenticaltolivingcarboncompounds.

Theglibdefinitionof“organicchemistry=carbonchemistry”doesneedsome
caveats,however.Forinstance,manygeologistsstudyarockcalledlimestone.
Limestoneismostlycomposedofamineralcalledcalcite,whichhasaformula
ofCaCO3.Thecarbonincalcite,andincarbonate(CO32-,HCO3-,CO2)in
general,isnotconsideredtobeorganic,sinceitformsbynon-biologic
processes.
Similarly,severalothersimplecompoundsarenotconsideredtobeorganic.
Theseincludehydrogencyanide(HCN),whichformsseveralinorganicsalts,
anddiamondandgraphite,whicharebothcarbonminerals,andsiliconcarbide
(SiC)andironcarbide,whichareminerals.
Amoreexhaustivedefinitionoforganicisthatthecarbonatomsofthemolecule
shouldbecovalentlyboundtoeitherhydrogenorcarbon(andpreferentially
hydrogenatsomepointinthestructure).Carbonthatformsionicbondsand
metallicbondsistypicallynotconsideredorganic.Similarly,graphiteand
diamondareessentiallypurecarbon,andaren’tconsideredorganic.
Naturallythere’safairbitoffuzzinesswithdeterminingwhetheracarboncontainingcompoundisorganicornot.Somedon’tfeelthatformaldehydeisan
organiccompound,whereastoothersitobviouslyis.ThesameistrueforHCN,
whichweidentifiedasinorganic.Somescientistsargueitisbetterdescribedas
organic.Intheend,mostofthecasesattheintersectionareintuitive.Aslongas


there’smorethanonecarbon,andit’sboundtoanothercarbonorhydrogen,you
cangenerallyassumethecompoundtobeorganic.
Notethatorganichasnothingtodowith“comingfromnature”,sothere’savast
differencebetweenorganicchemistryandtheorganicfoodthatyoumightbuyat
WholeFoodsorTraderJoe’s.Organicinchemistryprovidesnorealdiscerning
valueastoitsorigin,oritsinherent“health”.

KEYPOINTSANDHINTS:
Organicchemistryisthechemistryofcarbon,butnotallcarbon-bearing

moleculesareorganic.
Organiccarboncompoundsshouldhavecovalentbonds,andshouldhaveC-Cor
C-Hbonds.


2.Bondsinorganicchemistry

Bondingdiagramsinchemistryshowhowtheelectronsaredistributedin
compounds.Theelementcarbonhasanelectronicstructureof1s22s22p2
(rememberthatfromGenChem?).Thismeansthatcarbonhasfourvalence
electronsinthesecondshell.Itiscapableofformingfourbondswiththese
valenceelectrons.Althoughfivebondsdooccurasintermediatesortransition
states,thesearenotstable.Drawingastructurewithfivebondstocarbonhas
beengivenacolloquialnameof“TexasCarbon”(everything’sbiggerin
Texas!).Ifyoudrawamoleculewithfivebondstocarbon(includingdouble
bonds),you’veprobablydrawnitwrong.Becareful!
AcommonwayofrepresentingbondinginmoleculesisthroughaLewisdot
structure.LewisdotstructureswerefirstusedbyachemistGilbertLewis,who
designedthesediagramstoshowhowelectronsweresharedornot(notinvolved
inabond)betweendifferentatomsinabondormolecule.

Youcancalculatea“formalcharge”ofamoleculeby:
FC=NV–NU–BE/2
WhereFCistheformalcharge,NVisthenumberofvalenceelectrons(4for
carbon,5forN,6forO,etc.),NUisthenumberofunbondedelectrons,andBEis
thenumberofelectronsparticipatinginbonds.


TheLewisdotstructuremustbydefinitionshowallelectrons.Itisofteneasier
tosimplifysomeofthisbydrawingbondingelectronsasaline,insteadofdots.

Twolinesshowthere’sadoublebond,andthreeshowthere’satriplebond.
Electronsthatdon’tparticipateinbondsarestillshownexplicitlyinaLewisdot
structure.

KEYPOINTSANDHINTS:
Lewisdotstructuresshowbondsandunbondedelectrons.
Ifastructurehas5bondstocarbon,itisverylikelywrong!
Carbonalmostneverhasafreeelectronpaironit(exceptforcarbenes)

PracticeSections1&2?
Problem1
Problem2
Problem3
Problem4
Problem5
BacktoTOC


Problem1.
Identifywhichoftheseisanorganiccompound


A)CaCO3B)C60(AKAabuckyball)

C)N2D)H3C-CH3

Gobacktosection


YES!

Nextproblem?
Gobacktosection


No.


Gobacktoproblem
Gobacktosection


Problem2.
WhatistheLewisdotstructureforformaldehyde,H2CO?

A)

B)



C)


Gobacktosection

D)

YES!

Nextproblem?
Gobacktosection


No.


Gobacktoproblem
Gobacktosection


Problem3.
WhatisthecorrectbondingstructureforC2N2,AKAcyanogen?


A)



B)



C)

D)

Gobacktosection




YES!



Nextproblem?
Gobacktosection


No.


Gobacktoproblem
Gobacktosection


Problem4.
Providethecorrectstructureofpropane,C3H8.


A)

B)

C)

Gobacktosection

D)


YES!


Nextproblem?
Gobacktosection


No.

WatchoutforTexasCarbons!

Gobacktoproblem
Gobacktosection


Problem5.
WhatistheformalchargeofNinN2?

A)+5B)-3

C)0D)+3

Gobacktosection


YES!




Gobacktoproblem
Gobacktosection
BacktoTOC



No.


Gobacktoproblem
Gobacktosection


3.Molecularformula

Amolecularformulaisaquickwayofdescribingamolecule.Ittellsyou
specificallywhatelementsareinagivencompound.Itdiffersfromanempirical
formula,whichonlygivesasimplifiedversionofaformula.Empiricalformulas
arealmostneverusedinorganicchemistry,becausetoomuchinformationislost
whensimplifyingamolecularformuladowntoanempiricalformula.Asan
example,ethaneisC2H6.TheempiricalformulaforethaneisCH3.Toan

organicchemist,thelatterisvirtuallyuseless.
Themolecularformulacanalsobereorganizedintoasimplestructuralformula.
Intheaboveexampleofethane,theformulaofC2H6canberewrittenasH3CCH3
orCH3CH3.BothformulaenowgivethereaderabitofinsightastohowtheC
andHarebonded,betterthanC2H6.

Structuralformulaetakelongertowritethanmolecularformulae,butingeneral
theyarebetterastheyprovidemoreinformation.However,attimesamolecular
formulawillbetheonlyonethatwillwork.Considercyclohexane(C6H12):