CHEM 3710 Experiment #1 Lab Report Instructions Lewis Structures and Molecular Models

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Daisy Bridges
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1 CEM 3710 Exprimnt #1 Lb Rport Instructions Lwis Structurs nd Molculr Modls Rmmbr tht your notbook ntris r vry importnt nd tht you will b bl to us its contnt during th finl xm. Thus, kp thorough rcord of your nots nd obsrvtions. Lb Rport Nots (writtn in your lb notbook) Studnts my work with lb prtnr for th in-lb portion. Complt th rport t hom s ndd. Th lb rport is du t th bginning of th nxt lb sssion nd it nds to rflct th studnt s own work, no group work for lb rport writing. Bgin th lb rport on nw pg. Print clrly in your lb notbook so tht th crbon copis r lgibl. Lbl vrything you hnd in with your nm, dt, nd xprimnt numbr. Sction I Introduction (3 pts) (1 pt) Your Nm, Dt nd Titl of Exprimnt (2 pts) Nm two objctivs for this xprimnt Sction II Molculr Modls (dt rcordd during th lb, 21 pts) Problms 1-3 (9 pts) Build modl of (s blow). ) Giv th -C- bond ngl (1 pts) b) Giv th hybridiztion of C (1 pts) c) Indict whthr th molcul is polr (P) or non-polr (N), (1 pt) Problm 1 thn Problm 2 thn Problm 3 thyn (12 pts) Problm 4: Answr qustion #2 dscribd on pg 9 of your lb mnul. 1

2 Sction III Structurs nd Isomrs (dt rcordd during th lb, 16 pts) This sction will focus on th us of chmistry modl kit to undrstnd bonding nd structur. It is rquird tht you bring your modl kit to this lb your orgnic chmistry txtbook my provid hlpful informtion. Slctd ky concpts r rviwd blow. Blow pls find thr mthods for drwing 2-propnol, n lcohol with th hydroxyl group (-O) in th 2-position. Rviw ch rprsnttion (A-C) crfully. A) Th Condnsd Formul is writtn without showing ll th individul bonds. In th structur shown blow, C 3 indicts C tom with 3 ttchd toms, C(O) indicts C tom with n ttchd O nd n tom. B) Th Lwis Structur shows ll of th toms in structur nd ll its vlnc lctrons. Th shrd lctrons btwn toms r rprsntd s lin. Fr lctron pirs on C, N, nd O r drwn s dot for ch lctron or lin for n lctron pir. C) In th Lin-Angl Structur, th bonds r rprsntd by lins, nd crbon toms r ssumd to b prsnt whrvr two lins mt (=cornr of bnt) or lin bgins or nds. Elmnts othr thn crbon nd hydrogn r shown, such s nitrogn, oxygn, sulfur, phosphorus, nd hlogn toms (F,, Br, I). ydrogn toms r typiclly not shown unlss thy r ttchd to spcific tom such s N, O, S, or P. Condnsd Formul Lwis Structur (show ll lctrons) Lin-Angl Structur ( skltl drwing ) C 3 C(O)C 3 O C C C O 2-propnol 2-propnol 2-propnol Problm 5 Drw th Lwis structur (s B bov) nd th Lin-Angl Structur (s C bov) for ch of th condnsd structurs shown blow. In ch box, prctic drwing th structurs. (8pts) (C 3 ) 2 CC 2 (2 pts) C 3 C 2 C 2 C 2 (2 pts) (C 3 ) 3 C (2 pts) C 3 CC 2 C 3 (2 pts) 2

3 Isomrs r diffrnt compounds with th sm molculr formul. Thr r svrl typs of isomrs found in orgnic chmistry, mong othrs, thr r constitutionl isomrs. Constitutionl Isomrs r compounds with th sm molculr formul but diffrnt connctivity (= diffrnt squnc of bonds = diffrnt bonding pttrns). Shown in th box blow r condnsd formul of constitutionl isomrs for C Stroisomrs hv th sm molculr formul nd idnticl bonding connctivity but diffr in how thir toms r orintd in spc. For now, w will focus on cis nd trns isomrs: () cis cyclolkns cn hv groups (groups othr thn hydrogn, lso clld substitunts ) on th sm sid of th ring structur. (b) trns cyclolkns cn hv groups (groups othr thn hydrogn, lso clld substitunts ) on opposit sids of th ring structur. Problm 6 Isomrs (8 pts) In th spc providd blow, prctic drwing th Lwis Structur nd Lin-Angl Structur for ch of th C 4 10 isomrs bfor trnsfrring your good nswrs to th lb notbook. Condnsd Formul Lin-ngl structur Lwis Structur (2 pts) (2 pts) C 3 C 2 C 2 C 3 (2 pts) (2 pts) C 3 C(C 3 )C 3 Sction III Conformtionl Anlysis (dt rcordd during th lb, 8 pts) USE YOUR MOLECULAR MODEL SET to work on ths xrciss. Tk nots on this worksht. Thn trnsfr your good nswrs to your lb notbook. Includ dscriptions tht will hlp you rmmbr this xrcis nd ch tsk. Conformtionl Anlysis Atoms nd bonds rpl ch othr du to lctrosttic rpulsion btwn thir lctrons. Thr is strin whn th lctron clouds of toms in th molcul r too clos to ch othr; this is known s stric strin. To minimiz stric strin, th bonds nd toms in molcul prfr to b s fr wy from ch othr s possibl. Conformtionl nlysis is th study of th nrgy nd stbility btwn conformrs of molcul. Conformrs r structurs of th sm molcul tht ris s rsult of th rottion bout singl bond. Th dihdrl ngl (lso known s torsion ngl) is th ngl btwn two groups s you look down C-C bond. On usful wy to dpict conformrs is th Nwmn Projction. Th Nwmn projction looks down th C-C bond s shown in th figur blow (lft nd right), in which th substitunts r ithr stggrd or clipsd. Lrn how to corrlt Nwmn projctions to your molculr modls, nd how to convrt rgulr drwings into Nwmn projctions nd vic vrs. 3 C C 3 3 C Thr r thr min typs of conformtions: Syn (Eclipsd) Guch (Stggrd) Anti (Stggrd) 3

4 dihdrl ngl,! dihdrl ngl,! dihdrl ngl,! θ = 0º dihdrl ngl btwn nd θ = 60º dihdrl ngl btwn nd θ = 180º dihdrl ngl btwn nd ETANE Building modl of thn (C 3 C 3 ). Look down th C-C bond nd rott th bck crbon round th bond in 60 incrmnts, lving th front crbon of th molcul sttionry. Th rsulting viw givs th Nwmn projctions for thn. Fill in pproprit toms in th Nwmn projctions for thn blow. A B ow mny uniqu Nwmn conformtions do you obsrv? A molcul lso xprincs torsionl strin du to lctrosttic rpulsion of th lctrons in bond. Torsionl strin is th rsistnc to rottion bout singl bond cusd by th clipsd bond intrctions. Th figur blow shows th potntil nrgy of thn s th C 1 -C 2 bond in thn rotts. Th y-xis shows th potntil nrgy rltiv to th most stbl conformtions s th dihdrl ngl (θ) incrss. Problm 7 Which conformr of thn (A or B) do you think will b th highst in nrgy (lst stbl)? (2 pts) Explin your nswr. CYCLOEXANE Cyclohxns widly occur in nturl products. A vst numbr of compounds, including mny importnt phrmcuticl gnts, contin on or mor cyclohxn ring. Plnr cyclohxn dos not xist, instd it xists in chir form. If cyclohxn wr plnr, ll of th toms would b clipsd rsulting in both stric strin nd torsionl strin. In rlity, cyclohxn hs nithr torsionl strin nor ngl strin. Angl strin is obsrvd whn th bond ngl dvits from th idl ttrhdrl vlu (109.5º). Rthr, cyclohxn chivs ttrhdrl bond ngls (omitting stric strin) nd stggrd conformtion (omitting torsionl strin) by ssuming n rrngmnt tht chmists cll chir conformtion (s blow). Th chir conformtion is th most stbl form of ll possibl cyclohxn conformtions. Assmbl modl of cyclohxn in th chir conformtion nd plc your modl on th bnch. Notic how it is supportd by thr of th xil hydrogn toms ( ). Th othr thr xil hydrogn toms r dirctd up prpndiculr to th bnch. Notic lso tht th qutoril hydrogn ( ) toms r pointing towrds th qutor of th molcul. Ech C- bond is prlll on of th bonds in th ring. Now, convrt your ring into th othr possibl chir conformtion s shown blow nd prctic flipping from on chir form to th othr on. From lft to right (s blow), this is ccomplishs by pointing C 1 down nd C 4 up. 4

5 In th middl structur blow, put circl round ch of th 6-xil hydrogn toms nd box round ch of th 6- qutoril hydrogn toms. cyclohxn 4 1 = xil; = qutoril chir flip 4 1 Wht hppns to th qutoril hydrogn toms ( ) s th ring undrgos flip? Wht hppns to th xil hydrogn toms ( ) s th ring undrgos flip? Prctic drwing both chir conformtions of cyclohxn in th spc providd blow. Th chir cn b obtind by drwing thr sts of prlll lins. 5

6 SUBSTITUTED CYCLOEXANES Th hydrogns on cyclohxn do not hv to b shown t ll tims. owvr, rgrding othr toms / groups ttchd to th cyclohxn ring, it is importnt to rcogniz tht such groups (=substitunts) cn ssum two conformtions xil or qutoril. For xmpl, th mthyl group in mthylcyclohxn cn b in th qutoril or xil position s shown blow. Th nrgy of th conformr with th substitunt in th qutoril position is lowr in nrgy nd thrfor mor stbl; such conformr voids strin. Build modl of cis-4-mthylcyclohxnol. Th prfix cis rfrs to both substitunts bing on th sm sid. O this bond points wy ( ) cyclohxn O C 3 = C 3 = O C 3 this bond coms towrds you ( ) Problm 8 Drw both possibl chir conformtions. (6 pts) In th first structur show only th groups in th 1- nd 4-position. Thn drw th structur tht rsults from ring flip. [NOTE: Prctic th intrconvrsion of structurl rprsnttions. Modls r vry usful to undrstnding th 3-D spcts of chmicl structurs, th mor you us your modls th bttr you will undrstnd strochmistry]. A B Sction IV Conclusions (2 pts) List two nw things you lrnd in doing this xprimnt or somthing tht you now undrstnd bttr thn bfor you did th lb. Explin. Th lb rport is du t th bginning of th nxt lb sssion nd it nds to rflct th studnt s own work, no group work for lb rport ntris. Print clrly in your lb notbook so tht th crbon copis r lgibl. Lbl vrything you hnd in th duplict pgs with your nm, dt, nd xprimnt numbr. Sign & dt your lb rport 6

Instructions for Section 1

Instructions for Section 1 Instructions for Sction 1 Choos th rspons tht is corrct for th qustion. A corrct nswr scors 1, n incorrct nswr scors 0. Mrks will not b dductd for incorrct nswrs. You should ttmpt vry qustion. No mrks