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Chapter 18: Q3P. (page 923)

Why were no products from McLafferty rearrangement observed in the spectrum of butan-2-one?

Short Answer

Expert verified

Butan-2-one has no gamma γ hydrogen, so no products were present in the McLafferty rearrangement.

Step by step solution

01

McLaffertyRearrangement

The characteristic fragmentation of the molecular ion of a carbonyl compound (ketones and aldehydes) having at least one gamma γ hydrogen is known as the McLafferty rearrangement.

02

McLafferty Rearrangement Observed in the Spectrum of Butan-2-one

The structure of butan-2-one is shown below.

Since there is no gamma γ hydrogen in butan-2-one, so no products were observed in the McLafferty rearrangement.

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Most popular questions from this chapter

The Wittig reaction is useful for placing double bonds in less stable positions. For example, the following transformation is easily accomplished using a Wittig reaction

(a) Simple aminoacetals hydrolyze quickly and easily in dilute acid. Propose a mechanism for hydrolysis of the following aminoacetal:

(b) The nucleosides that make up DNA have heterocyclic rings linked to deoxyribose by an aminoacetal functional group. Point out the aminoacetal linkages in deoxycytidine and deoxyadenosine.

(c) The stability of our genetic code depends on the stability of DNA. We are fortunate that the aminoacetal linkages of DNA are not easily cleaved. Show why your mechanism for part (a) does not work so well with deoxycytidine and deoxyadenosine.

Question. The mass spectrum of unknown compound A shows a molecular ion at m/z 116 and prominent peaks at m/z 87 and m/z 101. Its UV spectrum shows no maximum above 200 nm. The IR and NMR spectra of A follow. When A is washed with dilute aqueous acid, extracted into dichloromethane , and the solvent evaporated, it gives a product B. B shows a strong carbonyl signal at 1715 cm-1in the IR spectrum and a weak maximum at 274nm(E =16) in the UV spectrum. The mass spectrum of B shows a molecular ion of m/z 72. Determine the structures of A and B, and show the fragmentation to account for the peaks at m/z 87 and 101.

Name the following ketones and aldehydes. When possible, give both a common name and an IUPAC name.

(a)CH3CO(CH2)4CH3 (b)CH3(CH2)2CO(CH2)2CH3 (c)CH3(CH2)CO(CH2)2CH3

(d)PhCOPh (e)CH3CH2CH2CHO (f)CH3COCH3

(g)CH3CH2CHBrCH2CH(CH3)CHO (h)Ph-CH=CH-CHO

(i)CH3CH=CH-CH=CH-CHO

(j) (k) (l)

Use equations to show the fragmentation leading to each numbered peak in the mass spectrum of cotane-2-one.
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