Chemistry 605 (Reich)

Transcription

1 Chemistry 60 (Reich) SECD UR EXAM Sat. April 9, 0 Question/oints R-A /0 R-B / R-C /0 R-D / R-E /0 R-F /0 Total /00 Average 6 i 9 Mode Median 6 AB 7 BC Distribution from grade list (average: 6.; count: 6) umber Grade ame Answer Key If you place answers anywhere else except in the spaces provided, (e.g. on the spectra or on extra pages) clearly indicate this on the answer sheets.

2 0 roblem R-A. Assign several of the protons and analyze multiplets of a steroid. 6 (a) Assign and analyze the following signals (report multiplicity and J values). Use the steroid numbering on the structure: δ. δ., tdd, J =, 7, 6 z, ddd, J = 7,, z δ.0 6, dt, J =, z (b) Assign the -proton signal between δ. and δ.7. Briefly provide a rationale for this assignment. What kind of multiplet is this? AB of ABX Apart from, and 6, the 6 protons will be the most downfield. The large J (9 z) also means the protons must be next to the keto group (c) Analyze this multiplet in a mathematically correct fashion (also show a coupling tree), using the frequencies given. Report coupling constants and chemical shifts. If two solutions are possible present them, and provide a rationale for choosing one of them. c - = 69.8 Δν ab- =. c + = 690. Δν ab+ =. Solution Solution J AB J AX J BX 6..6 ν A ν B ν AB 8..9 c - ± Δν ab- / = 70., 686. c + ± Δν ab+ / = 700.9, i=i δ A.60.7 δ B..6 Solution is correct - can't have a negative J, as in Sol. Also the Sol. couplings are unreasonably large A A 686. B Sol. Sol.

3 roblem R-A 70 Mz MR Spectrum in CDCl Source: Ieva Reich (/7) z, ddd, J = 7,, z 6, dt, J =, z, tdd, J =, 7, 6 z ax

4 roblem R-B. Compound R-B is a disubstituted naphthalene. Spectra of just the aromatic region are provided in two different mixtures of CDCl and C 6 D 6. From an analysis of the spectra, determine the positions of substitution. The substituents are: Me roblem R-B (C 6 8 ) 70 Mz MR Spectrum in C 6 D 6 /CDCl (/) (Source: Ieva Reich /) Me z roblem R-B (C 6 8 ) 70 Mz MR Spectrum in C 6 D 6 /CDCl (/) (Source: Ieva Reich /) z (a) Draw a possible structure, and label it with chemical shifts. Use the top spectrum for this, please. There are two patterns of,,-hydrogens 8.0 R (b) Is another substitution pattern consistent with the spectra? Explain. X 7. Upfield signals - this one should have the electron-donating Me group at position X Me 7. There is no way to determine the relative position of the substituents on the two rings with the information at hand Me

5 roblem R-C. You are given the structure of a pentose thiol triacetate and asked to determine the relative stereochemistry and conformation from the 70 Mz MR spectrum presented on the next page. (a) Analyze the sets of signals and show coupling constants in the standard format. When you have completed the analysis, assign the individual protons (e.g., ax ). Use the numbering system given on the structure in part (b). δ.7 dd, J =, 9 z This must be a from the chemical shift - coupled gem and ax-ax. Thus must be axial. δ.0 ddd, J =.,., z This must be e - coupled gem and eq-ax. There is also a W-coupling to the equatorial δ.9 dd, 8,. - br d, 8 - This is an AB pattern, one half is coupled to an X proton by ca. z, the other half is broadened. These must be the and protons, the is broadened by exchange of the S (which is a broad singlet at δ.7). The 8 z coupling between and means both protons are axial. The small coupling (. z) of to means is equatorial δ.07 ddd, J = 8.,., This is the proton at, coupled to the axial proton at C (9 z) and to the eq protons at C and C. Thus must be equatorial. δ. td,., This is the equatorial proton, coupled twice eq-ax (. z) to and. There is a small W coupling to e. (b) Determine the stereochemistry of R-0K. lace the appropriate substituents in each of the boxes on the structure below. e S Ac S Ac Ac Ac Ac a Ac (c) Briefly describe how you made the assignment at C-. a and e can be assigned from their chemical shifts (most upfield of the ring protons) and coupling patterns. a shows, in addition to the z gem coupling, a 9 z vicinal coupling, which means must be axial. can be assigned from the three couplings, two of which are to the protons.

6 roblem R-C (C 6 7 S) 70 Mz MR spectrum in CDCl (Source: aul Savage/Gellman /) Ac Ac S Ac e dd, J =.,., z a dd, J =, 9 z 8.6 dt,., ddd, J = 8.,., br d, 8 dd, 8, z Ac Ac Ac S S Curphy-Morrison: S. X -Alkyl.0 -Ac

7 roblem R-D. This problem requires you to interpret the partial 00 Mz MR spectrum of a,-dimethylpiperidine deuterated 9% on the -methyl group (source: F. A. L. Anet J. Am. Chem. Soc. 989,, 9) C C C D 6% 9% C z ormal Spectrum AB q of :: triplets J D =.8 z Deuterium decoupled AB q c = 07.7 J AB =.6 z ν AB = (.0) (.8) = 6.7 z δ.7 J ν A = / = 07. δ. ν B = / = 068. δ Identify all of the peaks in both the top and bottom spectra. Briefly explain the pattern, extract all coupling constants and determine exact chemical shifts, and report them in the standard format (e.g., δ., t, n J xy =. z). 9 The signals we are looking at are the -C protons (δ.7) and the -C -D protons (.-.7) In the deuterium decoupled spectrum the singlet at δ.7 is -C In D-decoupled the AB quartet centered at δ. is the -C -D group. The C group is diastereotopic (there is an asymmetric center at C-) and so forms an AB quartet. J AB =.7 z, δ A =., δ B =. ormal spectrum: each peak of the AB quartet is split into a :: triplet by coupling to D. J D =.7 z

8 0 roblem R-E (C 8 Si). In this problem you are given the structure of a phosphorus compound and asked to interpret parts of the MR spectrum. For each multiplet or set of multiplets report the pattern in the standard format: δ 0.00, triplet of pentets, n J XY = 0.0 z. You may use first order analysis. SiMe (a) Assign and interpret the three signals centered at δ C -C Me Si signal The two small peaks are 9 Si satellites J -Si = 7z (b) Assign and interpret the multiplet at δ 0.7. Draw and label a coupling tree. This is the -C -SiMe group - the protons are diastereotopic ( is an asymmetric center), so this is an ABX pattern X = B A J 7 J AB = z ( J ) δ A = 0.7 J AX = 6 z ( J - ) δ B = 0.78 J BX = 8 z ( J - ) (this is "AMX" treatment which always corresponds to Solution, not a proper ABX analysis, so if this happens to be a Solution situation, then the J's would be very wrong - they do look K though, and so Solution is probably fine) z J - J - J AX J BX (c) Assign and interpret the multiplets at δ Draw and label a coupling tree. ABM X Each pattern is a doublet of pentets, J = 0, 7 z for the diastereotopic -C -C group. The pentet arises because J to the C group and J are nearly the same J = 7 z J = 7 z J = 0 z We know the 0 z coupling is the gem J because of the size, and leaning effects (d) Assign and interpret the multiplet at δ 8.. This must be the proton ortho to the phosphonate group - approximately a ddd, J =, 6, z. There are some second-order effects, so couplings are suspect J = 8 z (ortho coupling) J = z (meta coupling) SiMe -C -C J = z (ortho coupling)

9 roblem R-E (C 8 Si) 00. Mz MR Spectrum in CDCl. Source:lafs Daugulis/Vedejs 08/ Et SiMe z B A X J B SiMe A J - J - J AX J BX Benzene Shifts Me Me d pentets (actually dqd) B A C J = 7 z J = 7 z d pentets (actually dqd) J = 0 z ddd, J =, 6, z J = 8 z (ortho coupling) J = z (meta coupling) J = z (ortho coupling)

10 0 roblem R-F. ere are the two parts of quiz 7 we didn't get to finish during my first lecture. ut your analysis (δ, J, multiplicity) in the space provide, and suggest some possible structures from the quiz answer sheet. Below are proton multiplets in different molecules. Analyze the pattern and extract the coupling constants. From the chemical shift given, what kind of protons are these likely to be? What part structures are suggested by this pattern? Find one or more molecules on the "MR Quiz Answers" sheet that fit the chemical shift and coupling pattern. (b) Integration: dd, J = 8, A B td, 8, z These are two aromatic protons ( A and B ), coupled to each other with J = 8 z (ortho). The upfield proton B has a second ortho coupling to C. Both protons are meta-coupled also, A to C, and B to D C D Y B A X B A Br also fit less well because J in pyridine are more varied (c) Integration: ddd, δ., J = 8., 8,. (almost a dt) ddd, δ.0, J = 9.0, 8., Most likely structure: A X A and B of an ABXY pattern C C B Y J / z h Coupling constants are consistent for those in a five-membered ring. They don't fit very well for chair cyclohexane + B A 9 Y X 8 B A

11 MR Quiz Answers ans Reich Chem 60 Et Et - CF Cl CF CF S S CF CF CF S Br SiMe SeC h SeC h Cl S 6 S Br h + h h C t Bu SiMe S Me S 6 Et h h Et Br