13C nmr chemical shifts have been recorded for a number of uracil, thiouracil, and pyrimidine derivatives. These data are discussed in relation to what is known of the lactam–lactim tautomerism in such systems and possible correlations of chemical shifts with normal aromatic substituent chemical shift parameters. The chemical shifts for the CH3 groups in simple methylated derivatives of uracil are very characteristic of the site of methylation and should prove useful as a tool for assigning structures to alkylated derivatives of this general type.

Ultrasonic absorption studies have been performed in dilute micellar solutions of Li, Na, and K octylsulfates, Na methylhexylsulfate, and Na hexylsulfate at 40" by the pulse technique in the range 13-143 MHz. Chemical relaxations associated with micelle formation were found In each system. The single-valued relaxation frequencies were concentration independent in solutions as concentrated as twice the c r~t~c a l m~celle concentration. The relaxation data can be accounted for in terms of monomermicelle association-dissociation.--Des etudes d'absorption ultrasonique ont Cte effectukes sur des solutions micellaires diluees d'octylsulfates de Li, Na et K, de mtthylhexylsulfate de Na et d'hexylsulfate de Na, a 40" par la mCthode des pulsations, entre 13 et 143 MHz. Des relaxations chimiques associees a la formation de micelles ont etC trouvkes dans chaque systeme. Les frequences de relaxation de valeur unique sont independantes de la concentration dans des solutions aussi concentrtes que deux fois la concentration critique en micelles. Les donnees de relaxation peuvent i t r e interprCtCes en termes d'association-dissociation monomeremicelle.[Traduit par le journal]Can.

13C nmr data have been obtained for a series of 2- and 4-pyrones and pyridones, and their sulfur-containing analogues. Correlations have been observed between the nature of the ring hetero-atom and the chemical shift difference (Δδ) for the Cα and Cβ carbons in these conjugated systems. No significant correlation, however, appears to exist between the chemical shifts of the C=O and C=S groups. Substituent chemical shift (s.c.s.) effects for various simple substituents are compared with those in related series of compounds.

Carbon-13 chemical shift data have been obtained for a number of isothiazole, benzo[c]isothiazole, 1,2-dithiole, and 1,3-dithiole derivatives. A number of these compounds are thiones and the chemical shifts of the C=S carbons are discussed in the light of recent attempts to predict such chemical shifts from those of the analogous carbonyl compounds. Comparisons of substituent chemical shift (s.c.s.) effects in these heterocyclic compounds with those in simpler aromatic or conjugated systems have been made and additivity correlations tested in a number of cases.

19F, 13C, and 1H chemical shifts have been determined for β,β-difluorostyrene and eight 4-substituted derivatives. The β-fluorine chemical shift difference, ΔδF, is used to evaluate the constant in the Buckingham equation. A = 3.0 × 10−11 esu for C—F bonds which is in excellent agreement with the value derived by Adcock and Khor. This allows accurate estimates of direct field effect contributions to 19F chemical shifts in aryl fluorides. Substituent parameter correlations demonstrate that the primary polar effect on 19F chemical shifts is field-induced π polarization. Abinitio molecular orbital calculations confirm that the substituent-induced 19F chemical shifts reflect changes in fluorine π electron density.