Mass spectrometric study of some pyrazoline derivatives

Abstract

The structures of some new carboxamide, thiocarboxamide, nicotinoyl and isonicotinoyl pyrazoline derivatives have been related to their mass spectral data. The ions produced under electron impact showed both the characteristic pyrazoline ion and unusual azete fragmentation patterns. These results suggest that the mass spectra of these pyrazoline derivatives are both position and substituent dependent. Fragmentations of the ions are discussed in view of their metastable transitions. # 1998 John Wiley & Sons, Ltd. Received 22 September 1997; Revised 31 March 1998; Accepted 26 April 1998 It has been reported that substituted pyrazoline derivatives possess a wide spectrum of biological activities and are crucial intermediates in the synthesis of substituted cyclopropane derivatives.1 Their mass spectra have been studied in some detail, and proven to be of use in structure determination.2 As a continuation of our work on the structure-reactivity of some erythro2,3-dibromo ketones with different nucleophiles that produce pyrazoline, 3 we investigate here electron impact induced fragmentation of some newly prepared compounds: DISCUSSIONThe characteristic peaks observed in the spectra of carboxamide and thiocarboxamide pyrazoline derivatives 1-3 are summarized in Scheme 1. Their spectra except for 1 exhibit molecular ion peaks and contain fragments that confirm the pyrazoline ring structure. 4 The most prominent ions in the spectrum of 1 show a depleted [M À 15] ion at m/z 284, this trisubstituted pyrazoline ion then eliminates carbonyl chloride to produce a diphenyl pyrazoline ion (base peak) at m/z 221, and subsequently produces phenyl pyrazoline ion at m/z 145 via loss of a phenyl radical. Ring fragmentation of the diphenyl pyrazoline ion gives two azirinium ions at m/z 119 and 118, or a tropylium ion at m/z 91. Peaks at m/z 77 and 65 are routinely observed in the degradation of the tropylium ion. The corresponding metastable ion peaks (Table 1) confirm these fragmentations.The degradation pattern of 2, as shown in Scheme 1, demonstrates a relatively low intensity molecular ion peak but a rather intense [M À H] ion. Formation of a diaryl substituted pyrazoline ion at m/z 267(base peak) involved a two-step elimination of an amide group from the pyrazoline ring. This substituted pyrazoline ion then dissociates further, producing the characteristic phenyl pyrazoline ion at m/z 145. In addition, as for 1, low-intensity azirinium ions and abundant tropylium and phenyl ions are formed following ring fragmentation of the phenyl pyrazoline ion. Interpretation of some of these processes is substantiated by observation of the appropriate metastable ion peak and tandem mass spectrometry (Fig. 1).The structure of the thiocarboxamide-2-pyrazoline derivative 3 is established from its mass spectral fragments, and in addition two metastable ion peaks are detected. The spectrum shows an [M À SH] ion at m/z 282. This is followed by elimination of HCN to produce a disubstituted pyrazoline ion at m/z 255 (base peak). Its ring ...

Synthesis, Characterization and Fluorescent Property Evaluation of 1,3,5-Triaryl-2-pyrazolines

“…A molecular ion peak (M + ) which was also the base peak was observed for all the synthesized 2-pyrazolines in their respective mass spectra. The fragmentation pattern of the synthesized compounds (exemplified by that of compound 6h ) matched the typical pattern of pyrazoline fragmentation [ 29 ] ( Figure 1 ), confirming the structure of compounds. On the basis of the combined physical and spectral data, compounds 1,3,5-triaryl-2-pyrazolines were assigned the structures shown in Figure 2 .…”

Homologous 1,3,5-triarylpyrazolines: synthesis, CH⋯π interactions guided self-assembly and effect of alkyloxy chain length on DNA binding properties

“…Furthermore, fragmentation pattern was also in good agreement with the already reported 2-pyrazoline derivatives. 52 The most stable fragment or base peak in compounds (1c-12c) was the molecular ion peak. The molecular mass data of all the synthesized 1,3,5-triarylpyrazolines (1c-12c) are provided in the experimental section.…”

Energy‐variable collision‐induced dissociation study of 1,3,5‐trisubstituted 2‐pyrazolines by electrospray mass spectrometry

“…7 Due to these diverse applications, many 2-pyrazoline derivatives were synthesized and their structure-activity relationships, as well as their fragmentation behavior under electron ionization (EI), were investigated. [8][9][10][11] In earlier studies, we have pointed out that 2-pyrazoline derivatives can easily be prepared by the reaction of a, b-unsaturated aldehydes or ketones with hydrazine derivatives. [12][13][14] As a continuation of our work, we now report the fragmentations of the protonated molecules of nine different 1,3,5-trisubstituted 2-pyrazoline derivatives under electrospray ionization (ESI) conditions using energy-variable collision-induced dissociation (CID).…”