Deuterium Isotope Effects of 0-Hydroxythioamides, Thiazolines and 5-Acyl-2-thiobarbituric Acids

Deuterium isotope effects on 13C chemical schifts are studied in a series of o-hydroxythioamides, 2 delta-thiazolines and enolic 5-acyl-2-thiobabituric acids. Novel 2-hydroxy-1-thiocarboxamide naphthalenes show steric isotope effects of opposite sign to those observed in 2-hydroxy-1-acetylnaphthalenes and pyrenes. The o-hydroxyaromatic 2delta-thiazolines show tautometric behaviour and accordingly large isotope effects. Tautomerism of these and the thioamides are discussed in relation to structure. Intramolecular hydrogen bonding of non-RAHB type show only weak effects. The enolic mono N-alkyl 5-acyl 2-thiobarbituric acids show two isomers, both of which are involved in enol-enol tautomerism.