215-216 HH W10-quiz 2-key

215-216 HH W10-quiz 2-key - Chem 215-216 HH W10 Name:_Key_...

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Quiz 2: January 22, 2010 Name:_____ Key __________________ Lab Section: Mon; Tue AM; Tue PM; Wed (circle one that applies); GSI _____________________ I. (3 points) The mass spectrum of an unknown hydrocarbon has a molecular ion peak with a relative intensity of 21.88% and an M+1 peak with a relative intensity of 1.69%. These relative intensities are against the base peak (100%). How many carbon atoms does the compound have? Show calculations. Please note that natural abundance of 12 C and 13 C is 99% and 1%, respectively. Answer: # of C’s is ___ 8 or 7 ___ Calculations: Let X be the number of carbon atoms; 99 : [1 x X] = 21.88 : 1.69 X = 7.7 However, if we use a more accurate 12 C : 13 C ratio (98.9 : 1.1), we get X = 6.9. II. (8 points) Shown below is the mass spectrum of 3-methyl-2-hexanone. Write the mechanisms responsible for the formation of the ions with m/z 43 and 72 from the molecular ion. Make sure to draw the structures of these fragment ions. (a) For m/z 43:
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215-216 HH W10-quiz 2-key - Chem 215-216 HH W10 Name:_Key_...

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