ISSN:0951-4198    

DOI:10.1002/rcm.1290021102

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021103

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

摘要:

Abstractcis‐Anellated 3‐methyl‐ (1) andcis(2)‐ andtrans(3)‐anellated 2,3‐dimethyl‐1,3‐perhydrobenzoxazines and the corresponding 3,1‐perhydrobenzoxazines (4, 5a, 5b, and 6, respectively) have been prepared and their configurations assigned with1H NMR spectroscopy. The electron‐impact induced fragmentations differentiate clearly the two sets of isomers since only the [MH]+and [MMe]+ions from 1–3 exhibit an appreciable retro Diels‐Alder reaction giving rise to the ionsm/z72 and/orm/z86. Besides the main reaction, elimination of methyl radical, isomers 5a, 5b and 6 also eliminate C3H 7−and C2H3O−forming the ions [C7H12NO]+and [C8H16N]+, atm/z126. The formation of the former is most favourable for 5a, 5b both for reasons of chemical composition and stereochemistry. The ion C6H10NO+atm/z112 represents the base peak of compound 4, i.e., a methyl group at the 2‐position is a better leaving group than a hydrogen atom and the ring nitrogen assists the α ‐cleavage of the cyclohexane ring in this case. Even the mass spectra of the isomericcis‐ andtrans‐annellated forms (2 vs 3 and 5a, 5b vs 6) can be distinguished from each other on the basis of some intensity differences caused by stereochemical effects. However, the two epimericcisforms 5a and 5b gave indistinguishable spectra. The characteristic decompositions have been verified by low resolution, high resolution, metastable and collision‐induced dissociation techniques. The compounds studied could not be differentiated based on their ammo

ISSN:0951-4198    

DOI:10.1002/rcm.1290021104

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021105

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021106

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

摘要:

AbstractThe possibilities for using the time‐of‐flight analyzer as a liquid chromatography detector are evaluated using a continuous flow probe and keV ion bombardment on a specially designed time‐of‐flight ins

ISSN:0951-4198    

DOI:10.1002/rcm.1290021107

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021108

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021109

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290021110

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY

摘要:

AbstractThe mass spectra of several compounds with molecular weights in the 2500–20 000 Da range were obtained with a quadrupole mass spectrometer equipped with an atmospheric pressure ion source. Average molecular weight determinations of mellitin (2846.4 Da), a synthetic oligonucleotide (4262.8 Da), myoglobin (16 950.4 Da) and on the subunits of β‐lactoglobulin (18 277.1 Da) requiring as little as 1 pmol of material were achieved with accuracies and precisions of ± 1 Da. An ion‐spray interface was used to produce ions via the ion evaporation process, producing mass spectra containing a series of multiply‐charged molecular species. A simple method for calculating the molecular weight of unknown compounds from the spectra containing multiply‐charged ions i

ISSN:0951-4198    

DOI:10.1002/rcm.1290021111

出版商:Heyden&Son Limited    

年代:1988

数据来源: WILEY