Ketones mass spectrum

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

Carvone is an unsaturated ketone responsible for the odor of spearmint. If car-vone has M+ = 150 in its mass spectrum and contains three double bonds and one ring, what is its molecular formula ... 

Ketones undergo a reduction when treated with sodium borohydride, NaBH What is the structure of the compound produced by reaction of 2-butanone with NaBH4 if it has an IR absorption at 3400 cm-1 and M+ = 74 in the mass spectrum ... 

To distinguish between azobenzene and benzophenone, assuming reference spectra are not available for these compounds, it is a good idea to examine the mass spectra of aromatic ketones, such as acetophenone, butyrophenone, diphenyldiketone, and so forth. Complete identification is assured by obtaining or synthesizing the suspected component and analyzing it on the GC/MS system under the same GC conditions. If the retention time and the mass spectrum agree, then the identification is confirmed. 

Oxoepistephamiersine (14) was isolated from the roots of Stephania japonica as the seventh hasubanalactam congener (77). The UV spectrum of oxoepistephamiersine (14) showed an absorption maximum at 284 nm, and the IR spectrum exhibited bands of a six-membered ketone at 1745 cm-1 and y-lactam at 1690 cm-1. The mass spectrum (Table V) revealed the most abundant ion peak at m/z 257, indicating stephamiersine-type cleavage (13). Since oxoepistephamiersine was identical to the y-lactam (14) derived from permanganate oxidation of epistephamiersine (77), structure 14 was proposed for oxoepistephamiersine (77). 

Interestingly, we were intrigued by the ESI mass spectrum of the compound, as the observed base peak consisted of [M-S02+Na]+. This led us to explore a thermal retro-Diels-Alder reaction that could afford the desired enone 69. It is noteworthy that the chemistry of cyclic enol-sulfites would appear to be an under-explored area with a few references reporting their isolation being found [57]. At last, we were also able to prepare epoxy ketone 70 from 69 in three steps, albeit epoxidation did not take place unless the TES group was removed. Spartan models reaffirmed our initial conformational assessment of enone 69 and epoxy ketone 70, which contain sp3-hybridized C8a and s/r-hybridized C8b (p s e u d o-. v/r - h y b r i d i zed C8b for 70) at the AB-ring junction (Fig. 8.12) and displayed the desired twisted-boat conformation in A-ring. 

The varnish on a modern painting ( Mont Saleve by Alexandre Perrier, 1916, private collection) showed a mass spectrum (Figure 5.19b) almost identical to that of Ketone Resin N. The use of a cyclohexanone resin as a picture varnish seems uncommon because copolymers such as AW2 were preferred by conservators [62]. An investigation into cyclohexanone resins by direct temperature-resolved MS (DTMS) is reported in the literature [22, 64]. Similar mass spectrometric patterns were achieved with masses accurately reflecting the values expected for the oligomers. 

When a ketone grows larger it does not necessarily imply that it has two identical alkyl groups at the carbonyl. In case of different alkyls at the carbonyl, Stevenson s rule may also be applied to decide which of them will dominantly be detected as part of the acylium ion and which should preferably give rise to a carbenium ion. Overall, a nonsymmetrical ketone will yield four primary fragment ions in its El mass spectrum... 

The secondary alcohol was smoothly oxidized to a ketone in high yield with pyridinium dichromate in dimethylformamide (cf 36). The IR spectrum indicated the presence of a ketone group bonded to the a-carbon of a thiophene (absorption at 1660 cm 1). The 200 MHz XH NMR spectrum showed all the features expected of this structure (cf Figure 12) as did the mass spectrum (cf. 1). 

Finally, the ketone was reduced by the modified Wolff-Kishner method (cf 8) to give the final product which was free of detectable amounts of the 2,4-isomer. The 200 MHz XH NMR and mass spectrum are both in accord with the structure (cf 1). Full details of this synthesis and spectroscopic properties of the intermediates and final products will be reported elsewhere. 

The mass spectrum of an unsymmetrical diaryl ketone, p-chlorobenzophenone, is displayed in Figure 1.23. The molecular ion peak (mlz 216) is prominent and the intensity of the M + 2 peak (33.99%, relative to the molecular ion peak)... 

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