2-Methyl-3 - pentanone spectrum

A lower molecular weight methyl ketone and an olefin are isolated as products of this reaction. That the enol is formed as a primary product which rearranges to the ketone follows from its detection in the IR spectrum of gaseous 2-pentanone upon photolysis. 3 In addition to the ketone and olefinic products, one usually obtains varying amounts of cyclobutanols. 

Spectrum A must be from 3-methyl-2-pentanone and spectrum B is from 3,3-dimethyl-2-butanone. 

A major fragmentation pathway in aldehydes and ketones is cleavage of the bonds to the carbonyl carbon. This process is similar to the fragmentation that occurs with alcohols and produces cations that are relatively stable because the octet rule is satisfied at all of the atoms. The major peaks at m/z 85 and m/z 43 in the spectrum of 4-methyl-2-pentanone (see Figure 15.13) result from this cleavage, as illustrated in the following equations ... 

The mass spectra of 3-methyl-2-pentanone and 4-mefhyl-2-pentanone are as follows. Explain which spectrum goes with which compound. What is the structure of the ion responsible for the peak at m/z 43 in each spectrum ... 

The shift reagent Eu(facam)3 has also been successfully used to determine the enantiomeric composition of a sample of D,L-3-methyl-3-phenyl-2-pentanone. The chiral shift reagent caused separation of some of the peaks arising from the two enantiomers. The spectrum of D,L-3-methyl-3-phenyl-2-pentanone in the presence of added Eu(facam)3 is shown in Fig. 10.22. The acyl methyl protons are well resolved as seen on the left side of the figure and their relative areas may be integrated. The optical purity of this sample... 

Fig. 10.22. Spectrum of a CCI4 solution of D,L-3-methyl-3-phenyl-2-pentanone in 0.5 M Eu(facam)3 [54],...

FIGURE 12.2 (a) H-decoupled 13C spectrum of 2-methyl-3-pentanone in CDCl3.The carbonyl resonance is not shown, (b) H coupled, 3C INEPT spectrum of the same sample. Note the CH doublet centered about 40.5 ppm, the CH2 triplet with the center line missing at 33 ppm, and the cwo CH3 quartets centered near 18 and 8 ppm. Courtesy of Herman J. C.Yeh (National Institutes of Health). 

FIGURE 12.3 (d) Pulse sequence for DEPT.Times indicated (0-6) are discussed in the text. (b) Example of DEPT applied to 2-methyl-3-pentanone, showing edited spectra from CH3) CH2, and CH carbons, as well as the decoupled I3C spectrum of the aliphatic carbons. Spectra courtesy of Herman J. C.Yeh (National Institutes of Health). 

A new alkaloid, crotalarine (17) has been isolated from Crotalaria burhia Buch.-Ham. The structure (17) proposed for crotalarine is based on alkaline hydrolysis to retronecine, 3-methyl-2-pentanone, lactic acid, and a lactone, crotalaric acid (18) the i.r. spectrum of which was similar to those of monocrotalic (19) and trichodesmic... 

Identify pairs of coupled protons in 2-methyl-3-pentanone, using the COSY spectrum in Figure 14.39. 

HETCOR spectrum of 2-methyl-3-pentanone. A HETCOR spectrum indicates coupling between protons and the carbons to which they are attached. 

Clearly, 2-D NMR techniques are not necessary for assigning the signals in the NMR spectrum of a simple compound such as 2-methyl-3-pentanone. However, in the case of many complicated molecules, signals can be assigned only with the aid of 2-D NMR. 

Pentanone will produce m/z 58 via McLafferty rearrangement, whereas no such product will be formed in the El spectrum of 3-methyl-2-butanone. 

In the mass spectrum of 4-methyl-2-pentanone a McLafferty rearrangement and two other major fragmentation pathways occur. Propose reasonable structures for these fragment ions and specify the m/z value for each. 

You have two bottles (A and B), but the labels have fallen off and blown away. You know that one is 3-pentanone and the other is methyl butanoate. You take a mass spectrum and an infrared spectrum of each to help determine their identity. Describe how you would distinguish A and B. 

FIGURE 2.3 Shift of methyl overtone peaks top spectrum is hexane, middle is 3-pentanone, and bottom is acetone. 

Library WileyS Spectrum 69746 Name 2-Pentanone, 4-hydroxy-4-methyl... 

FIGURE 6.43 Proton NMR spectrum of 4-hydroxy-4-methyl-2-pentanone. 

The absorption spectrum of 4-methyl-2-pentanone is compared with that of several other ketones in figure IX-D-18, and tabular data are given in table IX-D-8. Data from a single gas-phase, 313 nm photolysis experiment with the pure ketone (120 C, pressure 49Torr) by Martin and Pitts (1955), suggest that there is little discrimination in bond breakage in (I) and (II). From co, c3H6-0rv 0.35. 

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