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Chapter 13: Q 39. (page 522)

Question:Primary (1°) alcohols often show a peak in their mass spectra at m/z= 31. Suggest a structure for this fragment.

Short Answer

Expert verified

Answer

Structure of the fragment that shows peak at m/z = 31

Step by step solution

01

α cleavage of alcohols

Alcohols undergo fragmentation to give a dehydrated radical cation and cations and neutral radicals uponα cleavage.

02

Step 2: α cleavage of primary alcohols

Primary alcohols can cleave to form an alkyl radical and a carbocation containing the alcohol group. This carbocation is resonance stabilized and has an m/z value of 31.

The cleavage of a primary alcohol is shown below:

αcleavageof primary alcohol

The cation formed is resonance stabilized; the canonical structure is shown below:

Resonance stabilization of the carbocation formed

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Most popular questions from this chapter

Question: How would each of the following pairs of compounds differ in their IR spectra?

Question: Match each compound to its IR spectrum.

Question: The mass spectrum of the following compound shows fragments at m/z = 127, 113, and 85. Propose structures for the ions that give rise to these peaks.

Question: Propose structures consistent with each set of data: (a) a hydrocarbon with a molecular ion at m/z = 68 and IR absorptions at 3310, 3000–2850, and 2120 cm−1;

(b) a compound containing C, H, and O with a molecular ion at m/z = 60 and IR absorptions at 3600–3200 and 3000–2850 cm−1.

Question:2,3-Dimethylbutane and 2,2-dimethylbutane have the same molecular ion in the mass spectrum, but only one of these isomers gives a significant fragment at m/z= 57.

(a) Whichisomer shows an intense peak at m/z= 57?

(b) Propose a structure for the ion that gives riseto this peak.

(c) The base peak in the mass spectrum of the other isomer occurs at m/z= 43.

What ion gives rise to this peak?
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