Deuterium isotope effects of o-hydroxythioamides, (2)Delta-thiazolines and5-acyl-2-thiobarbituric acids

Deuterium isotope effects on C-13 chemical shifts are studied in a series o f o-hydroxythioamides, (2)Delta-thiazolines and enolic 5-acyl-2-thiobarbitu ric acids. Novel 2-hydroxy-1-thiocarboxamide naphthalenes show steric isoto pe effects of opposite sign to those observed in 2-hydroxy-1-acetylnaphthal enes and pyrenes. The o-hydroxyaromatic (2)Delta-thiazolines show tautomeri c behaviour and accordingly large isotope effects. Tautomerism of these and the thioamides are discussed in relation to structure. Intramolecular hydr ogen bonding of non-RAHB type show only weak effects. The enolic mono N-alk yl 5-acyl 2-thiobarbituric acids show two isomers, both of which are involv ed in enol-enol tautomerism.