On the mechanism of isomerization in the esters of some α,β‐unsaturated carboxylic acids—II

Burgers, Peter C.; Terlouw, Johan K.; Vijfhuizen, Peter C.

doi:10.1002/oms.1210131109

Cited by 9 publications

(4 citation statements)

References 12 publications

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“…The loss of a COOH' radical is also indicative of an [ester]+' -+ [acid]+' isomerization ( Table 1). 6 Trideuteriomethyl esters lose only COOD', which indicates that there would seem to be no H/D exchanges in the deuteriated acid ions formed. This fragmentation is missing in the trichloro isomers 7 and 14, however, showing that the isomerization of their molecular ions does not occur.…”

Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

“…In addition to 1, the loss of H,O is detected only in 2 and 6 ( Table 1). The probable intermediate ions d' and d" formed from [2]+' and [6]" would produce the chlorinated 2-butenoic acid molecular ions e', er' and e"', which are believed to be the cis forms7 (Scheme 3).…”

Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

“…No loss of chloroketene was detected, however. Certainly, loss of CHClCO from the saturated 2-chloro esters has been shown to give very weak peaks, the fragment ion of chloroketene owing to its instability being hardly Hence, it is possible that 3,4-dichloro-2-butenoic acid molecular ion formed from [6]" would isomerize into the 3,4dichloro-3-butenoic acid molecular ion,…”

Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

“…A phenyl group present at the a-or 6position of the vinylic double bond, however, appears to suppress this [ester]+' -+ [acid]+' isomerization by promoting other reactions or opening up new reaction pathways. 6 In the present paper the mass spectral fragmentation of the methyl and trideuteriomethyl esters of all seven chlorinated propenoic acids and the chloromethyl ester of propenoic acid has been investigated with the aid of the 1st FFR metastable ions. The effect of a chlorine substituent on the isomerization in the ionized esters of chloropropenoic acids is discussed L .…”

Section: Introducfionmentioning

confidence: 99%

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Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

Korhonen¹

1983

Org. Mass Spectrom.

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Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters. a-Cleavage, [M-OCH,]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of HzO, CH3' and COOH' indicate the isomerization of some ionized chloro esters to the chlorinated 2-butenoic acid molecular ions. An intense loss of HzO observed for methyl 2-chloropropenoate indicates its most facile isomerhation, [ester]'' --f [acid]", whereas the isomerhation in methyl trichloropropenoate could not be observed. The molecular ion of chloromethyl propenoate, however, also seems to partly rearrange to the chlorinated 3-butenoic acid ion, since the first field free region metastable peak shows a weak loss of CO. me new reaction pathways, i.e. the losses of CHO', CHzO and CHzCO from ionized chloromethyl propenoate, were detected. INTRODUCfIONEarlier papers in this series concerned the mass spectral fragmentation of all methyl chloropropanoates,' methyl mono-and dichlorobutanoates' and methyl and chloromethyl esters of monochlorinated 2,2-dimethylpropanoic, 2-methylbutanoic, 3-methylbutanoic and pentanoic acids.3The fragmentation of unsaturated carboxylic acid derivatives has been widely investigated, some papers dealing with the mass spectra of methyl propenoates.L6 The behaviour of halogenated unsaturated esters does not appear to have been discussed.It has been shown previously from a detailed examination of the first field free region metastable peak shapes, that the molecular ion of methyl propenoate rearranges into 2-and 3-butenoic acid ions prior to metastable fragmentations involving the losses of In the present paper the mass spectral fragmentation of the methyl and trideuteriomethyl esters of all seven chlorinated propenoic acids and the chloromethyl ester of propenoic acid has been investigated with the aid of the 1st FFR metastable ions. The effect of a chlorine substituent on the isomerization in the ionized esters of chloropropenoic acids is discussed and the results are compared with those of the methyl propenoates reported earlier.536 RESULTS AND DISCUSSIONThe following esters were investigated: CH,=CCl-COOCH, CHz=CCl-COOCD, 1 8

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Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

Section: B) the Key Intermediate Ion In The [Ester]+' -+ [Acid]+'mentioning

confidence: 99%

Section: Introducfionmentioning

confidence: 99%

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Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

Korhonen¹

1983

Org. Mass Spectrom.

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Mass spectra of halogenated esters. Part IX—methyl esters of 2-butenoic acids containing chlorine and/or bromine atom(s)

Korhonen

1990

Biol. Mass Spectrom.

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The electron impact mass spectra of methyl esters of chloro-, bromo-, dichloro-, bromochloro-and dibromo-2-butenoic acids (13 esters at all) have been investigated. Generally, the peaks due to the following fragments areCharacteristic for the 2-and 4-halo isomers are the primary losses of a methyl radical and methanol, and for the %halo isomers the loss of X from M". Disparities between the spectra of the E and 2 isomers are shown, the effect of position of halogen substitution being much more pronounced, as reported previously with the halogenated propenoic acid esters.

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Site of protonation in the chemical ionization mass spectra of olefinic methyl esters

Harrison¹,

Ichikawa²

1980

Org. Mass Spectrom.

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The H2 and CH, chemical ionization mass spectra of the olefinic esters methyl acrylate, methyl methacrylate, methyl crotonate, methyl 3-butenoate, methyl 2-methyl-2-butenoate, methyl 3-methyl-2-butenoate and methyl cinnamate have been determined. In addition to the expected loss of CH,OH from [MH]+, in many cases the protonated molecules also show loss of CO or CH&O with methoxy group migration to the positive ion centre, indicative of protonation at the double bond. These rearrangement reactions, which have analogies in electron impact mass spectra, result in chemical ionization mass spectra of isomeric molecules which show more substantial differences than the electron impact mass spectra. In the case of methyl cinnamate, isotopic labelling experiments show considerable interchange of the added proton with the ortho and metu phenyl hydrogens prior to CH@H or CH&O loss, although the extent of interchange is not the same for both cases.Although there have been numerous investigations'-' of the electron impact (EI) mass spectra of acyclic unsaturated esters, including two recent reportsg310 of extensive isomerization of molecular ions prior to fragmentation, there do not appear to have been any studies of the chemical ionization (CI) mass spectra of this class of compounds. The behaviour under CI conditions of saturated methyl esters is relatively well under~tood;"-'~ however, the addition of a second functional group has been s h o~n '~,~~ to exert a strong influence on the CI mass spectra observed. The present work reports the H, and CH, CI mass spectra of the methyl esters of some unsaturated (primarily a-p) carboxylic acids, undertaken to probe the influence of the olefinic bond on the CI behaviour of methyl esters. As will be shown below elimination of C O and/or CH,CO from the protonated molecule [MH]+ is frequently observed, and is indicative of protonation at the double bond. The CO and CH,CO elimination reactions are analogous to rearrangement reactions observed earlier in EI Methyl acrylateBoth the H, and CH, CI mass spectra of methyl acrylate are unexceptional. In the H2 CI spectrum m/z 55, [MH-CH,OH]+, is the base peak with the only other ions observed being mlz 59, the [ C H 3 0 G O ] + ion and [MH]+, which are 20% and 10% of the base peak respectively. In the CH, CI, the [MH]' ion is the base peak with mlz 55 having a relative abundance of -10% and an even weaker m/z 59 ion signal. Use of deuterated reagent gases (D, and CD,) showed that the added proton is contained in the neutral fragment in both fragmentation reactions.I' Permanent address: Hoshi College of Pharmacy, Tokyo, Japan Methyl methacrylate, methyl crotonate and methyl 3-butenoateThe H,, D,, CH, and CD, CI mass spectra of these three isomeric methyl esters are given in Figs 1-3 and show much more pronounced differences than one observes in their EI spectra. is observed in the H, and D, CI spectra only. The CH, CI shows the same primary fragmentation reactions, with the extent of fragmentation being much less, as anticipated. The D2 and ...

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On the mechanism of isomerization in the esters of some α,β‐unsaturated carboxylic acids—II

Cited by 9 publications

References 12 publications

Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

Mass spectra of halogenated esters. Part IX—methyl esters of 2-butenoic acids containing chlorine and/or bromine atom(s)

Site of protonation in the chemical ionization mass spectra of olefinic methyl esters

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