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Low‐energy, low‐temperature mass spectra. 10—urethanes
Author(s) -
Bowen Richard D.,
Maccoll Allan
Publication year - 1989
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210240210
Subject(s) - mass spectrum , ion , chemistry , branching (polymer chemistry) , polyatomic ion , bond cleavage , electron ionization , metastability , crystallography , carbon fibers , carbon atom , spectral line , cleavage (geology) , stereochemistry , medicinal chemistry , alkyl , materials science , organic chemistry , physics , ionization , catalysis , astronomy , fracture (geology) , composite number , composite material
The 12.1 eV, 75°C electron impact mass spectra of 24 urethanes, RNHCO 2 C 2 H 5 [R H, C 2 H 2 n +1 ( n = 1‐8), CH 2 CHCH 2 , Ph, PhCH 2 and PhCH 2 CH 2 ], and seven symmetrically disubstituted urethanes R 2 NCO 2 C 2 H 5 (R C n H 2n + 1 ( n = 1−4)) are reported and discussed. All 31 spectra show appreciable molecular ion peaks. For n −C n H 2 n +1 NHCO 2 C 2 H 5 , M + ˙ usually is the most abundant ion in the spectrum. A peak at m / z 102 of comparable intensity also is present; this corresponds to formal cleavage of the bond connecting the α‐ and β‐carbon atoms in the N ‐alkyl group, though it is unlikely that the daughter ion has the structure [CH 2 NHCO 2 C 2 H 5 ] + . In the RNHCO 2 C 2 H 5 series, branching at the α‐carbon atom enhances the relative abundance of the ion arising by notional α‐cleavage at the expense of that of M + ˙ . Formal cleavage of the bond between β‐ and γ‐carbon atoms occurs to some extent for [RNHCO 2 C 2 H 5 ] + ˙ ions; this reaction provides information on the degree of branching at the β‐carbon, especially if metastable molecular ions are considered. The higher n ‐C n H 2 n +1 NHCO 2 C 2 H 5 ( n = 5−8) urethanes exhibit two other significant ions in their mass spectra. First, there is a peak at [M C 2 H 5 ] + . Secondly, a peak is present at m / z 90; the most plausible structure for this ion is [H 2 N(HO)COC 2 H 5 ] + , arising by double hydrogen transfer from the alkyl group and expulsion of a [C n H 2 n −1 ]˙ radical. Ions originating from secondary decomposition of the primary ionic species are generally of only very low abundance in these spectra.