2011 Exam 2 Key - Exam Score CHM 255 Bonus pts Exam 2...

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Unformatted text preview: Exam Score CHM 255 Bonus pts Exam 2 (March ll, 2009) Name (Print) g : rd 6 Instructions: Answer in the spaces provided. Write the answers in pen only] (Exams written in pencil will not be re—graded!). A table of axial vs. equatorial free energies, a supplement to that table, and a table of IR absorption bands are attached. Also, worksheets are attached for your use; nothing written on these worksheets will be considered for grading. This exam is 6 pages Total Score 1. (70 pts) Answer the following questions by circling the correct answer(s) or by inserting a response. a. (4 pts) On the structure below, circle the hydro gen(s) that is/are partly responsible for an axial methyl group having a higher 6" than that of an equatorial methyl group. H CH3 H H H H b. (6 pts) Provide IUPAC names for the following compounds: Br 0) H/U We. [0 130723518 (ii) M W» I) :3 r c. (4 pts) Circle the common name for the structure drawn below. H H/Br H Phenyl bromide allyl bromide Vinyl bromide ethyl bromide (d) (9 pts) Lower energy light corresponds (w shorter) wavelength and (higher, frequency. Wavenumbers are units of(l/h,@1/v). (e) (12 pts) Answer True (T) or False (F). i. Ail pairs of stereoisomers are either configurational or conformation isomers F) ii. The con '1 ration of an R chiral center is converted to S by rotation of 180° (T, iii. :ach member of a pair of diastereomers must be chiral by definition (T, iv. chiral compound need not have a chiral center F). (f) (6 pts) The absorption band corresponding to the stretching vibration of the C“: group is always less) intense than that for C=C because of the (smaller, change in dipole ' ment resulting from the C20 stretch. (g) (9 pts) Label the structures drawn below as chiral or achiral. Br CH3 cram-13 ‘ (i) Cflscflzgcm W/ Br CH3 (ii) :brg/ “CH3 H Br (iii) OH . Hf : c2 ah gig / (h) (4 pts) Label the structure drawn below as E or Z. H\ /CH2CH3 Hocn2 \CH3 E (i) (6 pts) Label the following chiral centers as R or 8. CH3 H 0) EC/ 8 Br/ \NHZ H, CH3 (ii) “I CH3 CH3 L CH3O (1') (6 pts) 0 i. The theoretical bond angle for H-C-H in ethylene (see below) is g Q; . H \ ‘2 (/C m on2 H ii. Answer True (T) or False (F). is—Z—Butene slowly isomerizes to the trans isomer at room temperature. (T, (k) (4 pts) A compound has two different chiral centers; circle the one (or more) of the following that represents a pair of diastereomers. C;C2 CICZ RS RS RS SR 2. (15 pts) Examine the table of free energies and the su iemental free ener information attached to this exam. i. (4 pts) Why is the effect of an axial iodine atom smaller than that of a chlorine atom when the iodine atom is clearly the larger of the two? Becwge‘f'ke C27: Jammy/e %afl‘7%e C~Cl 7%5 Me ii. (4 pts) Why is the effect of a _C a CH group so much smaller than that of a _CH=CH2 grou ? I 6‘ :fl» 8% 7%919 ate-W 2. @749st ‘MG PM iii. ( ts) Draw the two chair conformations corresponding to the structure drawn below, circle the one that is lower in energy and calculate their difference in AG" values. CH3 c K GHB \\‘CH3 1 Cfié \ m M (W; #ficfl CC #32:. emetic; 44-3 afar/c974 a? Z“ “swfigz CMQ/ dB“:- «ax/Y hwywa/g tawekefi-I/Qt‘ 054329.38, kcgflwg bEflW¢e 2"” afiéwy’wé alga/[eny 3. (15 pts) Shown below are the structures of 6 compounds. Also shown are 3 IR spectra. Insert the code letter of the compound responsible for that spectrum in the space provided to the right of the spectrum. COZH CHQOH CHB\ G O /cmCHCHQCH2CaCH CH3 A B c D l onto O—CCH3 E F [DD {IFNSHITTENCEI ' I (II D [DD runsut RNCEI'I (n a {DD TIIHSHITTWKEI' I 01 I: {000 3000 2090 mm 1000 500 NRVENUHBERI «I 1310!) 300D 2009 lfiflCl 1000 50 HRVENUHE Efll-Ii dllOD 3000 20m 1500 1000 EEO KR‘VENUHE E.“ -II Bonus (10 pts) Conjugated dienes can rotate about the central C—C bond at room temperature (see below). Thus, solutions of these dienes consist of a mixture of the two rotational isomers. However, the diene (X) shown below exists as only one isomer (Le. it is 100% the structure shown as “X”). Provide an explanation for this fact. {ZZZ f "X" £0 kw V t79+§7é5 " H // 2L-QWWS V ...
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This note was uploaded on 03/12/2012 for the course CHEM 255 taught by Professor Chemolski during the Spring '10 term at Purdue University-West Lafayette.

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2011 Exam 2 Key - Exam Score CHM 255 Bonus pts Exam 2...

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