11-10 - 11/12/2010 molecular formula of X = C6H12...

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Unformatted text preview: 11/12/2010 molecular formula of X = C6H12 Ozonolysis of X gave two compounds, Y (CH2O) and Z (C5H10O) What is the structure of X? H Y= O C H H molecular formula of X = C6H12 Ozonolysis of X gave two compounds, Y (CH2O) and Z (C5H10O) What is the structure of X? Y= O C H H partial structure number peaks from vicinal coupling = n + 1 n = number of vicinal hydrogens (adjacent) H A B C D E nmr spectrum of Z nmr spectrum of Z molecular formula of X = C6H12 Ozonolysis of X gave two compounds, Y (CH2O) and Z (C5H10O) What is the structure of X? number peaks from vicinal coupling = n + 1 n = number of vicinal hydrogens (adjacent) How many differences in two spin states are present in the following spectrum? A.=1 B.=2 C.=3 D.=5 E.=7 A B C D E 3 vicinal Hs 2 vicinal Hs nmr spectrum of Z an an NMR spectrum at 300 MHz = 900 Hz 3.0 ppm Do the hydrogen nuclei in the same molecule experience different magnetic fields? A. True B. False 9 8 7 6 10 9 8 7 6 ppm 5 4 3 2 1 0 Why? 10 ppm 5 4 3 2 1 0 ∆E ∆E energy ∆E ∆E energy ∆E = 300 MHz = 300,000,000 Hz ∆E = 300,000,900 Hz ∆E – ∆E = 900 Hz 5 1 11/12/2010 What is the magnetic field at a hydrogen nucleus? induced magnetic field What is the magnetic field at a hydrogen nucleus? induced magnetic field H H ∆E ∆E Is the actual field experienced by the hydrogen in a molecule A. greater or B. less than the applied field? applied magnetic field required for H resonance actual field at shielded nucleus is less than the applied field. 7 applied magnetic field required for H resonance 8 The magnetic field experienced by a given proton depends upon the fields induced by the electrons. If the electron density at the hydrogen atom is decreased would the strength of the actual magnetic field (A) increase or (B) decrease? A. Increase B. Decrease C H O C H actual magnetic field applied magnetic field 9 actual magnetic field applied magnetic field10 The graph below displays the chemical shifts of the circled hydrogens. Which hydrogen atom would you predict to be at 4 ppm? ∆E ∆E Would the circled hydrogen be expected to occur in region A or B of the following spectrum? A 1 0 10 9 8 7 H H H O H H O NH NH O H O O H H HO H HO O OO O 11 H H O O B 4 3 10 9 8 7 H H 6 ppm 5 4 3 H A. H O H O H B. O O O OH OH deshielding of hydrogen nuclei 2 6 ppm 5 deshielding of hydrogen nuclei 2 1 0 H O NH NH H H H OH OH O H H HO H HO O OO O O H H H O 12 2 11/12/2010 chemical shift ? H H H O H O NH NH H O H O O H H HO H HO O OO O O H H H O O OH OH Would the field at the aromatic H be A. greater or B. less than the aliphatic H. H C H H H C H H H H H ? applied field 13 actual field at H actual field at H 14 chemical shift Assign the indicated hydrogen atoms to the nmr spectrum in the following molecule. aromatic aromatic H H H H O H H H CH CH3 methyl methylene methylene A. aromatic = A. methylene = methyl = B. aromatic = methylene = methyl = C. aromatic = methylene = methyl = D. aromatic = methylene = methyl = H H C ∆E ∆E 10 9 8 7 6 ppm 5 4 3 2 1 0 15 16 16 The area under the peaks in a H nmr spectrum are proportional to the different types of hydrogens. aromatic aromatic H H H H O H H H CH CH3 methyl methylene methylene Which of the following hydrogens would you expect to be furthest to the right in the 1H nmr spectrum. Electronegativities: O = 3.5 C = 2.5 H = 2.1 A CH H methylene H methyl - β 3 B O CH3 methyl - α peak area = 5 3 C deshielding of hydrogen nuclei 2 17 18 3 11/12/2010 Assign the indicated hydrogen atoms to the nmr spectrum in the following molecule. A. methyl - β = A. methylene = methyl - α = B. methyl - β = methylene = methyl - α = C. methyl - β = methylene = methyl - α = D. methyl - β = methylene = methyl - α = Why is the circled methyl group three lines rather than a single line in the nmr spectrum? B. Because the adjacent hydrogens are diastereotopic. H CH3 O CH3 O CH3 H H H CH3 A. Because the magnetic moments of the adjacent hydrogens affect the local field around the CH3 group. H CH3 methyl - β O methylene H CH3 methyl - α 1H NMR spectrum for 2-butanone 19 20 Why is the middle line 2x the others? H CH3 H H CH3 H H CH3 H applied field CH3 H H CH3 actual field ∆E actual field ∆E ∆E actual field O higher energy required to induce a nuclear spin transition. 2 ? ? lower energy required to induce a nuclear spin transition. 0 21 1 4 ...
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