Modified uracils convertible between cations, conjugated, and cross-conjugated mesomeric betaines. Syntheses, semiempirical study, and X-ray analysis

Nucleophilic substitution on the 6-chlorouracils (1) and (8) by heteroaroma tics such as DMAP, 4-methylpyridine, and 3-hydroxypyridine yielded uracilyl pyridinium salts (2, 3, 7, 10), mesomeric betaines (4, 5, 6), and a bis-bet aine (9), respectively. A prototropic shift converts the CCMB (6A) into the CMB (6B), the dipole moments and most stable conformations of which were c alculated. X-Ray crystallography was performed on the uracilylpyridinium sa lt (7).