UK CHE 230 - Chemistry 230 First Examination

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page 1Chemistry 230 First ExaminationSeptember 18, 2000Name (please PRINT LEGIBLY) (last) (first)Student ID # Problem Score1. (a-d) /292. (a-c) /153. (a-b) /094. (a-e) /125. (a-b) /256. (a-d) /10Total /100Please observe the following.1) Write LARGE and LEGIBLY.2) Read each question carefully before answering.3) For questions with multiple parts, be consistent. Your answer to a later part will begraded based on the earlier part being correct, whether or not it actually is. For example,suppose I asked the following questions:(a) What is the hybridization of methane? (5 pts)(b) What is the H–C–H bond angle? (5 pts)Three students gave the following answers: Student 1 Student 2 Student 3 (a) sp2sp2sp3(b) 120° 109° 109°Score: 0 pts + 5 pts 0 pts + 0 pts 5 pts + 5 ptsStudent 1 correctly answered (b) given her answer for (a). Student 2 incorrectly answered(b) given his answer for (a), even though (b) is formally correct. Student 3 correctlyanswered both (a) and (b) and got full credit for the question.page 21. (29 pts. total.) Consider the acetonitrilium ion, [CH3CNH]+.(a) (4 pts.) How many valence electrons does [CH3CNH]+ have? (Note the charge!)(b) (5 pts.) Using the σ bond network drawn below as a starting point, draw the BESTresonance structure for the acetonitrilium ion. Be sure to show all lone pairs.CHHHCNH(c) (6 pts.) Looking at the structure you just drew, what are the hybridizations of:the left-hand C? the right-hand C? the N? (d) (4 pts.) Considering your answer to (c), what is the C–C–N bond angle in theacetonitrilium ion?page 3(e) (10 pts.) Draw a diagram showing all of the atomic orbitals in the acetonitrilium ion.Indicate which atomic orbitals overlap to form σ bonds, which ones overlap to form πbonds, and which ones hold unshared electrons. I’ve drawn out the C–H bonds to get youstarted. (Note: For sake of clarity, please don’t draw the small back lobes of the hybridorbitals.)CHCHHNssp3σsp3sp3ssσσHpage 42. (5 pts. each, 15 pts. total.) The best resonance structure of each of the followingcompounds is shown. Draw the second best resonance structure (or an equally goodresonance structure) of each one.(a)NH2HHH(b)HCH3CH3(c)HHHHHpage 53. (9 pts. total) The structures of uridine (an RNA base), thymidine (a DNA base), andAZT (an anti-AIDS drug), are shown.NOOHHOHNOOOOHHOthymidineC1C2uridineNHNOOAZTCH3ONHONHNOOCH3NNC3C3C2OH(a) (4 pts.) How many hydrogen atoms does uridine have?Use words, not numbers, to answer part (b).(b) (5 pts.) What is the oxidation state :of C1 in uridine? of C2 in uridine? of C2 in thymidine? of C3 in thymidine? of C3 in AZT?page 6(4) (12 pts. total.)(a) How many degrees of unsaturation does C5H7ClO have? (4 pts.)(b) Draw an isomer of C5H7ClO that contains a ketone (CCCO). (There are many correctanswers.) (4 pts.)(c) Draw an isomer of C5H7ClO that does not contain a ketone. (Again, there are manycorrect answers.) (4 pts.)page 7(5) (5 pts. each, 25 pts. total.) For each pair of compounds, indicate the relationship of thesecond compound to the first by circling the best answer.(a)is a skeletal isomer ofis a resonance structure ofis the same compound as (not a resonance structure of)is not an isomer, but has the same functional group ashas none of the above relationships toH2NNH2(b)OHOHHO OHis a skeletal isomer ofis a resonance structure ofis the same compound as (not a resonance structure of)is not an isomer, but has the same functional group ashas none of the above relationships to(c)HNHNis a skeletal isomer ofis a resonance structure ofis the same compound as (not a resonance structure of)is not an isomer, but has the same functional group ashas none of the above relationships topage 8(d)is a skeletal isomer ofis a resonance structure ofis the same compound as (not a resonance structure of)is not an isomer, but has the same functional group ashas none of the above relationships to(e)Cl Br Cl Bris a skeletal isomer ofis a resonance structure ofis the same compound as (not a resonance structure of)is not an isomer, but has the same functional group ashas none of the above relationships topage 96. (5 points each, 10 points total.) Amides are usually much lower in energy than thecorresponding ketones because a low-energy resonance structure (B) can be drawn for anamide that cannot be drawn for the ketone:NO NONOOOABCACHowever, the tricyclic amide 1 is higher in energy than the corresponding ketone 2, partlybecause resonance structure B cannot be drawn for amide 1.NO1O2(a) There are two different (but related) reasons why resonance structure B can’t be drawnfor amide 1. Give one. (Think about the geometry of the atoms and the orientation of theorbitals in space.)(b) The disallowance of resonance structure B for amide 1 should make amide 1 equal inenergy to ketone 2, but in fact it is higher in energy. What other factor makes amide 1higher in energy than ketone 2? Hint: Compare the second-best resonance structures inamide 1 and ketone


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UK CHE 230 - Chemistry 230 First Examination

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