OrganicStructuresShapesandIsomerism Part1KathyCarriganVersion 42-0183-00-01                                                                                                                          Lab Report Assistant                                                                                                  Thisdocumentisnotmeanttobeasubstitute foraformallaboratoryreport.TheLabReport Assistantissimplyasummaryoftheexperiment’squestions, diagramsifneeded,anddatatables thatshouldbeaddressedinaformallabreport.Theintentistofacilitatestudents’writing oflab reports by providing this informationin an editable filewhich can be sent to an instructor.   PartI:The TetrahedralCarbon Atom A.  Examine one of thecarbonatoms.Howmanyprongs arefound in themodel carbonatom? four   B.   Inserta shortstickinto each prong of the carbon atom. What do these sticks represent?     C.   Howmanycovalentbonds arenecessaryforeachcarbonatomin an organicmolecule?     D.  Whatisthebondanglerepresentedbyanypairofsticks;notethatallpairsofstickshave identicalbond angles.     E.   What causes these bonds to be symmetrically arranged about the carbon atom?     PartII:AlkanesandAlkylGroups AlkanesandAlkylGroups.Alkanesare hydrocarboncompoundswhichcontainonlysinglebonds andaresaidtobesaturated.Theyarenamedaccordingtothelongestcontinuouschainofcarbon atoms.   A.  Constructamodelofamethanemoleculebyaddingahydrogen(whiteball)toeachofthe4 bondsinyourcarbonmodelfromA-2.Drawthestructural(2-dimensional)formularepresented by this model. Recall the VSEPR Theory to determine the molecular structure for this molecule. Molecular structure = ex (this one is done for you, using the insert symbols in Microsoftword)  1.   Does this molecular structure look like the molecule you have drawn? Explain.   Youarenowbeingaskedtovisualizemoleculesbyputtingonyour“imaginary3-D”glasses.Every time youseethestructuralformulaofanorganicmoleculeyoushouldrealizethatthepaper drawnstructureisonlyonewayofdepictingthemolecule.Eachelectronpairwillaffecttheshape ofmoleculeswhichwillaffectthemoleculesphysicalandchemicalproperties.This1-carbon groupiscalledmethane,andisthesimplestalkane.It,andallalkanes,followthegenericformula of CnH(2n + 2), where n represents the number of carbon atoms in the longest continuouschain. Froma2-dimensionaldrawingofdichloromethane(CH2Cl2)itwouldappearthattwodifferentdichloromethanesexist.   B.   Constructamodelofdichloromethanebyreplacing2ofthewhiteballsonmethanewith greenballs. 1.   Whatdoesyour3-dimensionalmodeltellyouaboutthe“equivalency”ofthe2-dimensionalmodels of dichloromethaneshown above? 2.   Are the structures differentor are they the same?   Now: C.   Replacethechlorineatomswithhydrogenatomstomakemethaneagain;thenremoveoneofthehydrogenatoms(butnotthebond)fromyourmethanemodel.Thisisthesimplestexample   of an “alkyl group”. Alkyl groups donot exist as unique molecules, rather they are addedto the structures of larger alkanes and other carbon compounds.Draw the structural formula for this methylgroup.            This1-carbongroupiscalledamethylgroup,andhastheformulaCH3.Alkylgroupsoflargercarbonnumber havethegeneralformula of CnH(2n+ 1). 1.   What would be the formula for an ethylgroup(2 carbonatoms)?   2.   Drawthe structuralformula fortheethylgroup(leavethebond in)            Addacarbonshouldhavebeenaddhydrogen,ourfaulttothebondonthemethylgroupandadd3 hydrogen atoms and bonds (You are essentiallyconnecting2 methyl groups). 1.   What is the formula for this compound?   2.   What is the name of this compound?   3.   Drawthe structuralformula forthis compound.   4.   What is the molecular geometry on each carbon atom?   Rotate the molecule by grasping one methyl group in each hand. 5.   Is free rotationabout a single bond possible?   Rotatethemoleculeuntil thehydrogensareina“staggered”arrangement.Rotatethemolecule againuntilthehydrogensaredirectlyovereachother(eclipsed).Thisrepresentationofethaneis called a Fisher Projection.    6.   Whichconformation(form)wouldyoupredictwouldbefavored?Explain.(Remember that the sticks represent negativelycharged electron pairs.)     D.  Remove one of the hydrogen atoms. 1.   Does it matterwhich one you remove?   2.   Are all six hydrogens of the ethane molecule “equivalent”?   3.   Drawthe structuralformula forthis alkylgroup.   4.   What is the name of this alkylgroup?   E.   Unite this alkyl group with a methyl group (Build another methyl group). 1.   Drawthe structuralformula forthis new hydrocarbon.          b.   Does the model you built look like the structure you drew?   c.   What is the molecular formula for this new compound?   d.   What is the name of this compound?   e.   What is the molecular geometry on each carbon atom?   Examine thearrangementsof hydrogenatomsin this newmodel. f.    Aretheyall equivalent?  Testthis byremovingone of thehydrogenatomsfromone of theendcarbonsof this structure. g.   Draw the structural formula for this alkyl group, the propylgroup.   Beginwithpropane againand removea hydrogenatomfromthecentralcarbon. h.   Draw the structural formula for this, the isopropylgroup.            Look at the number of hydrogen and carbon atoms in methane, ethane and propane. i.           Whatisthedifferenceinthenumberofcarbonatomsbetweenmethaneandethane;andbetweenethaneand propane?   j.           Whatisthedifferenceinthenumberofhydrogenatomsbetweenmethaneandethane;and betweenethaneand propane?   Aseriesofcompoundshavingthisconstantdifference iscalledahomologous(homogeneous) series.vAlkanes(orsaturatedhydrocarbons)belongtothehomologousseries whichhasthe generalformula CnH(2n+ 2). k.   What is the formula for the 6-carbon alkane?   Build the six carbon alkane molecule. l.            What is the name of this compound?   m.Drawthe structuralformula forthis compound.   n.   What is the geometry on each carbon atom?   o.   Does the structural formula look like your model? Explain?     PartIII:Isomerism Isomers(iso=same;mer=part)arecompoundsthathavethesamemolecularformulas(same#ofC’sandH’s)butdifferineitherposition/connectivity(structuralisomer)orangle/shape(geometricisomer)ofattachment.Moleculesarenotisomersiftheycanbeturnedintooneanother without breaking any bonds. Build a molecule of butane. (noteseeTable 1on page2) a.   What is the molecular formula of butane?   b.   Drawthe structuralformula of butane.            Nowremovethemethylgroupforoneoftheendsofbutaneandswitchitwiththehydrogen atomon the remainingmiddle carbonatom.The nameof this compoundis 2-methylpropane. c.   Drawthe structuralformula of this molecule.   d.   What is the molecular formula of 2-methylpropane?   e.   Whatisthenamegiventomoleculesthathavethesamemolecular formula,butdifferentstructuralformulas?     Challenge Question(required) A.  Drawstructuralformulas  forthe2differentstructures  containing  four  carbons  and  10hydrogens.                           1.   Write the name of each under the structures. 2.   Howdo thesemolecular formulas compare?   Whattermisusedtodescribecompoundswiththesamemolecularformulabutdifferentstructuralformulas?   Challenge Questions(required) Therearethreepossiblestructuralisomersofpentane(C5H12).Useyourmodelkittodetermine these structures and draw structural formulas for these isomers, and name each one. Hints: Also drawn as:      Note:  Start  at  one  end  and  count  from the  beginning  of  each  line  to  denote  a C  atom.  It  is  “understood”  each  carbon has 4 bonds, therefore the end carbon’s have 3 H’s andthe 3 middle C’s have 2 H’s understoodbonded tothem. Thisoneisdrawnusingthe drawing program.        Note: Each C has 4 bonds, andtherefore hasthetetrahedral structurewiththe bond angle of 109.50.     n- Pentane You may draw the remaining 2 structures here, and name them. Or you may draw the structures on your on paper and only write the names here, both receive full credit.     Wearelooking toenhancethe coursebyintroducingyou tothedrawingprograms tohelpyouin chem.106.Goahead,giveitatry,ifthenamesarecorrect,wewillgiveyoufullcreditevenifthe structureshaveerrors. Constructmodelsanddrawthefourstructuralisomersofdichloropropane(C3H6Cl2), actually the remaining 3. Nameeachone.Oneisgivenasanexample.(Youmaydrawthestructures,andnamethem.Oryoumaydrawthe structureson youron paperand only writethenameshere.) Ex. #1= 1,2-dichloropropane     Alsodrawnas:       Cycloalkanes- Hydrocarboncompoundsarrangedincircles. Constructa model of cyclopropane:          What is the bond angle between the 3 carbon atoms?Think triangles! What is the bond angle in a tetrahedral carbon atom (see page 1)? What is the molecular formula for cyclobutane.Whenforcingthebondanglesawayfromtheidealanglesinthetetrahedralgeometrythebonds become more “strained” or unstable. Is cyclopropanemoreorless stablethan propane? Explain.     Constructa model of cyclobutane:   What is the bond angle between carbons in this molecule? What is the molecular formula for cyclobutane.Which would you predict to be more stable cyclopropane or cyclobutane?Explain.     Construct a model for cyclohexane, REALLY build it, it WILL make a difference!   (it is important to make sure your sticksor bonds are the same length):  Study the model you built, does your model look like the structure drawn above? What is the approximate bond angle between carbon atoms in your model?Itisimportanttonotethatthe2-Dstructuralformulasarehelpfultoseetheconnectivityof atoms.Themodelsyoubuildwillhelpyoutoseethe3-Doractualstructureofthemoleculesdue totheelectronpair repulsionand actual bond angles.   Would you expect cyclohexane to be more or less stable than cyclopropane?Explain!          Notethatbypuckeringandbuckling,thecyclicstructurecanhavetwodifferentstructures(conformations),a boat and chair form.      Replace a hydrogen atom with a methyl group on cyclohexane. Reviewthestructureandmolecularformulaofmethylcyclohaxane.Wouldthiscompoundbepolar ornonpolar covalent.   Would this molecule be soluble in water? Explain.      Would this molecule have a high vapor pressure or a low vapor pressure?Explain.