M. Pykalainen et al., SATURATED HETEROCYCLES .228. TAUTOMERISM OF SOME AMINO DIOL AND AMINOALCOHOL DERIVATIVES IN THE GAS-PHASE, Rapid communications in mass spectrometry, 9(10), 1995, pp. 916-920
The mass spectrometric behaviour of condensation products of nine subs
tituted benzaldehydes with 3-amino-1,2-propanediol and 3-amino-1-pheno
xy-2-propanol was studied under electron impact and chemical ionizatio
n. The 70 eV electron impact mass spectra showed that, as in solution,
the amino diol derivatives existed as three different structural isom
ers in the gas phase: viz. open-chain Schiff base, oxazolidine and tet
rahydro-1,3-oxazine, The fragmentations revealed a large amount of the
decomposed molecular ions to have the open-chain structure, but also
that the amount of both ring forms was considerable, In the same way,
with the amino alcohol derivatives both the open-chain and the oxazoli
dine ring forms were present in the gas phase. In all cases, the ring
formation was much more favourable in the gas phase than in solution,
Substituents at the phenyl ring caused changes in the relative amounts
of the different forms: electron-withdrawing substituents shifted the
equilibria in favour of the ring forms while electron-donating substi
tuents favoured the open-chain form, Under chemical ionization, methan
e, isobutane and acetone were used as reagent gas. Methane was the onl
y reagent gas that led to some fragmentation of the protonated molecul
es.