Exam II Solved - Organic Chemistry I - Summer 2008 | CHEM 3311, Exams of Organic Chemistry

Download Exam II Solved - Organic Chemistry I - Summer 2008 | CHEM 3311 and more Exams Organic Chemistry in PDF only on Docsity! You -~ Frow 2 Summer 2008 a Ll Circle the best answer for each of the following questions (20 pts). la. Which of the following structures represents 2-methylpentane? H H Ho! CH, H3C CHs Hy _UCHsCH3 4H CH3 ee HA HO CH Hg” 7H H ‘CHyCHy \ H CH3 Hgc™ *H H” “CH2CH3 ZZ lb. Which of the following molccules has the most angle strain? (>) oO Oo C) Ne Ic. Which of the following molecules is 2,2,4,4-tetramethylhcxanc? id. Which of the following monosubstituted cyclohexanes would exhibit the greatest preference for having the substituent in an equatorial position? H3C CH; Gis CHZCHg or ~ le. What is the relationship of substituents A and B on this substituted cyclohexane? gauche anti eclipsed none of these choices i 2a, Draw these three CgH)4 constitutional isomers (6 pis): NN ALN hexane / 2-methylpentane : 2,3-dimethylbutane 2b. Put a circle around the compound with the lowest boiling point (3 pts). 2c. Draw the three compounds on the potential cncrgy diagram at the appropriate levels to correctly reflect their relative AH combustion Values (3 pts). — AHcombustion (kcal/mol) Av 2 CoHyg + 19 Oo 12.COz + 14 Hed Sa. In each of the following pairs of acids, circle the stronger acid (6 pis). Then, for one of the pairs only, provide an explanation to support your choice. Use words and properly drawn chemical structures in your explanation (4 pts). 9 f oo. | , AL of & iC ‘ ny SE LN HyC” “OH \_Fx07 “OH PEAS 10’, ‘o Air we & Lo © wets? Rom! P Both Coniugate bases ark Stalled be, be LOUOMLE , Conjugate bese Show at right hag ad dihova ableton wa trucker elechon wir drawal Hz 2 Fs, Bauing GF on C, woes woxt b@® sbhilus thy Hoare thou: ge. HN Cow) a im tore Stable Conjugate base _ DO wore EN than N, dechons hatch Wore Tha tg (closer to wun) (roow| H-C=C-H | or ae ae 4 @etczcuH vs, Q : { Wore Stable Hes L Conjugate | bage ~ uv ss Stable, lone parr Is In an Con ake base ~ Sp ovbilel aud Thus lone pod in sp * ob bite , re . Is lA wewe Closely te ; re fon plows, nucleus (us oe 5 Chaya TY cheser b waa cbeus, stabilned b by posse Chaat, f fey wuckenes) 6. Ethane has two important conformations, eclipsed and staggered. In class, we discussed the fact that the energy difference between two structures often can be understood from two approaches: Structure A is stabilized in a way that Structure B is not, or Structure B is destabilized in a way that Structure A is not. Provide an argument for each of the following two statements. Use bath words and drawings, as needed, to support your arguments (12 pts). Eclipsed ethane is destabilized relative to staggered ethane. TAY u7 > H ~ , H lovsronad shaun fa Staggered chant dees not ecliosed ethane races haut Hus dectabWeohan . Hie, polenra eetray of ; he’s corbmatchoin . Staggered ethane is stabilized relative to eclipsed ethane. Staggewd ethane expereuces hy perernjuge hoo an ns ran é oe inkrachon of Liled anc Crap ovbitals In ad \aceut bowels hac lowers Hig erty of elechong. “The orbitals muslued arg a Chom (Riled) ont a CHG*: emphy — filed AD oe 4 i 7. All the data we have seen in class suggest that substituents on six-membered rings such as cyclohexane prefer to occupy equatorial positions, when possible, to minimize strain. However, in molecules like the one shown below, the hydroxyl group shows a strong preference for an axial bond. This phenomenon is called the anomeric effect and at least two distinct arguments have been made to explain the observed preference. Propose an argument that explains why the hydroxyl group prefers to occupy an axial position in the compound shown here. Provide any structures or drawings that will help support your explanation. (Hint: [f there were no oxygen atom in the ring, the hydroxy! group would prefer an equatorial position.) (8 pts) Tu 5 { laua hors 4 lwo possible “ee me lg pavial reso La dipoles ave alvs wk ia Such, ba a way as to fhe 3 xX pole Luaray just ae ey we Saw jn Aipole- chipols ‘ Intt eo lo ener ove. “ i out fog hypervorjugahon behvern a lowe parr (a Btled ovbrtat) on Om HS nag aud a t-0 o* (emphy ovbi tel 0 (Dra wing the exact Skane og the C-O9 lepovtaut” as long as yor get tO b re Wot So mp LY He gewrrod (doa. Tot hy pe reonjucg ation 0 is frvolved -) ~H Oro