Tautomerism of some amino diol and amino alcohol derivatives in the gas, phase1

Abstract

AbstractThe mass spectrometric behaviour of condensation products of nine substituted benzaldehydes with 3‐amino‐1,2‐propanediol and 3‐amino‐1‐phenoxy‐2‐propanol was studied under electron impact and chemical ionization. The 70 eV electron impact mass spectra showed that, as in solution, the amino diol derivatives existed as three different structural isomers in the gas phase: viz. open‐chain Schiff base, oxazolidine and tetrahydro‐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 oxazolidine 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 substituents favoured the open‐chain form. Under chemical ionization, methane, isobutane and acetone were used as reagent gas. Methane was the only reagent gas that led to some fragmentation of the protonated molecules.