chapter12

Why does the base peak have the mass it does p 435 13

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Unformatted text preview: 13 Mass Spectrum Interpretation Handout Dr. Cowley's handout on mass spectrum interpretation was discussed in lecture. 14 Problem 12.27 C3 H C 3C2C2CC3 H H H HH 2-Methylpentane (C6H14) has the mass spectrum shown below. Which peak is M+? Which is the base peak B+? Propose structures for the fragment ions of m/z 71, 57, 43 and 29. Why does the base peak have the mass it does? B+ = 43 M+ is very small, typical of an alkane. M+ = 86 p. 435 15 Problem 12.27 C3 H C 3C2C2CC3 H H H HH 2-Methylpentane (C6H14) has the mass spectrum shown below. Which peak is M+? Which is the base peak B+? Propose structures for the fragment ions of m/z 71, 57, 43 and 29. Why does the base peak have the mass it does? (It is stable carbcation.) + CH2CHCH3 m/z = 43 + CH2CH m/z = 29 + CH2CH(CH3)2 m/z = 57 (- mass 29) + CH3CH2CH2CHCH3 m/z = 71 (- mass 15) p. 435 16 Practice Problem 12.4 Assume you have two unlabeled samples, on of methylcyclohexane and the other of ethylcyclopentane. How could you use mass spectrometry to tell them apart? They have the same molecular formula (C7H14), but very different mass spectra. The mass spectrum is like a fingerprint for that compound. Fig. 12-6, p. 414 17 Practice Problem 12.4 Assume you have two unlabeled samples, on of methylcyclohexane and the other of ethylcyclopentane. How could you use mass spectrometry to tell them apart? M+ = 98 Mass...
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