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215 HH W10-E1-key - Name_Key 215 H H W 10-E xam N o 1 P age...

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Name_________ Key __________________ 215 HH W10-Exam No. 1 Page 2 I (14 points) Identify the indicated pairs of hydrogens in each of the following compounds as (i) homotopic, (ii) enantiotopic, or (iii) diastereotopic Hs. Write the answers as (i), (ii), or (iii). Also write the number of unique H’s and C’s for each compound. H 3 C H 3 C O O H a H b CH 3 CH 3 H 3 C O O CH 3 H a H c H b H d H CH 3 H e H f H 3 C H 3 C O O H a H b CH 3 CH 3 (a) (b) (c) H a and H b : _______ H a and H c : _______ H a and H d : _______ H b and H d : _______ H c and H d : _______ H e and H f : _______ Number of unique H's: __________ Number of unique C's: __________ H a and H b : _______ Number of unique H's: __________ Number of unique C's: __________ H a and H b : _______ Number of unique H's: __________ Number of unique C's: __________ 4 5 i ii ii ii iii iii iii ii 6 5 3 4 II (16 points) A dichloride compound, C 4 H 8 Cl 2 , has the following spectroscopic properties. 1 H NMR (in CDCl 3 ) δ 1.94 (4H, triplet, J = 7.0 Hz) and 3.58 ppm (4H, triplet, J = 7.0 Hz); 13 C NMR (in CDCl 3 ) δ 29.78 and 44.21 ppm. (1) The mass spectrum of the dichloride shows a number of peaks corresponding to its molecular ions due to the isotopes of Cl atoms. Show below the isotope distribution of the molecular ions. The natural abundance of the two Cl isotopes, 35 Cl and 37 Cl, is 75% and 25%, respectively. Ignore the presence of 13 C isotopes. Show in the box below how you calculated the peak intensity ratios. Make sure to write m/Z valaues. m/Z relative intensity Molecular ion peaks Calculations: 126 128 130 m/z 126 peak = 56 + 35 + 35 m/z 128 peak = 56 + 35 + 37 and 56 + 37 + 35 m/z 130 peak = 56 + 37 + 37 C 4 H 8 Cl 2 = 56 + Cl + Cl Probability = 3/4 x 3/4 = 9/16 Probability = 3/4 x 1/4 = 3/16 Probability = 3/4 x 1/4 = 3/16 Probability = 1/4 x 1/4 = 1/16 Therefore, the peak intensity ratio among m/z 126, 128, and 130 peaks is: 9/16 : 2x3/16 : 1/16 = 9 : 6 : 1 (2) In the box below the structure of this dichloride and assign both 1 H and 13 C chemical shifts by writing chemical shift values next to the corresponding nuclei.
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