Carbonyl groups mass spectra

The 4-Hydroxy-thiazoles are characterized by infrared absorption near 1610 cm (KBr) (3) or 1620 to 16.S0cm (CCI4) (8), indicating a strongly polarized carbonyl group. H-5 resonates near 5.6 ppm in the NMR spectrum like similar protons in other mesoionic compounds (3). Two fragmentations of the molecular ion are observed in the mass spectra. The first involves rupture of the 1,2 and 3,4 bonds with loss of C2R 0S . In the second, the 1,5 and 3,4 bonds are cleaved with elimination of C2R 0. ... 

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... 

Compound 37a showed the absence of an aldehydic proton and the singlet around 8.15 ppm was assigned to the ethylenic proton located p with respect to the electron-withdrawing cyano and ester groups. The benzofuranyl coumarins 38 exhibited the carbonyl-stretching band around 1690 cm in the IR spectra (Table 6). PMR data for 13 compounds are given in Table 2. The El mass spectrum of 36a showed a molecular ion peak at m/z 324 (41%). 

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... 

Comparison of the HREI-MS of N-formylstaurosporine (309) with (+)-stauro-sporine (295) (see Scheme 2.74) indicated the presence of an additional carbonyl group. The EI-MS spectrum mass fragmentation ion at m/z 466 (M -CO) indicated the presence of a formyl group. Additionally, the presence of an aldehyde functionality was confirmed by the characteristic IR bands at v ax 1670 (C = 0), 2840 (aldehyde CH) cm The and C-NMR spectra of N-formylstaurosporine... 

Dioxo-3-isoparteine was isolated from Lupinus sericeus (143). The mass spectrum, with M+ at miz 262 and signals at miz 234 (M" — 28) and 206 (M+ - 56), is characteristic for 10- and 17-oxosparteines and successive splitting of two carbonyl groups. Oxidation of p-isosparteine (14) by potassium ferricyanide resulted in 10-oxosparteine (108) as well as 10,17-dioxo-p-isospar-teine (109) (Scheme 13). This confirmed the alkaloid structure. Although 109 was found as a natural compound it had already been synthesized by Bohlmann et al. (144). The problems of configuration and conformation of sparteine (6), a-isosparteine (7), and (3-isosparteine (14) were discussed (145). 

Epiaphylline was isolated ftomLupinus hartwegii (146-147). The mass spectrum of this alkaloid is characterized by peaks at m/z 248 (70), 247 (46), 220 (45), 137 (47), 136 (100), 97 (53), and 96 (45%) that are tyical for sparteine alkaloids. The peak at m/z 220 originates from the splitting of a carbonyl group. Epiaphylline (110), in contrast to aphylline (108), did not react under mild catalytic hydrogenation conditions, but under harsher conditions epiaphylline (110) converted to 3-isosparteine (14) (Scheme 14). This established the presence of a carbonyl group at C-10. 

The 111 NMR, 13C NMR (NMR - nuclear magnetic resonance), infrared (IR), ultraviolet (UV), and mass spectrometry (MS) data have been reported for the first example 5 of a 2/7-azepin-2-one (2-azatropone). The carbonyl group stretching frequency appeared at 1682 cm 1 in the IR spectrum of the neat material <2000JOC6093>. Further H and 13C NMR spectroscopic data on azepine derivatives have been summarized by Smalley <1997HOU(E9d)108>. 

Carboxylic acids. Monocarboxylic acids normally show the molecular ion in the spectrum. Cleavage of bonds adjacent to the carbonyl group (a-cleavage) results in formation of fragments of mass M — 17 (OH) and M — 45 (C02H). Characteristic peaks arise from the McLafferty rearrangement. 

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