Structure and Hydrogen Bonding of Solid N1-Alkyl-N2-arylthioureas. 13C CP/MAS, IR and Semi-Empirical AM1 Studies

✍ Scribed by Iwona Wawer; Vera Koleva

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 434 KB
• Volume: 34
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199603)34:3<207::aid-omr858>3.0.co;2-0

✦ Synopsis

Seven crystalline N'-alkyl-N2-arylthioureas were studied by I3C CP/MAS NMR and by IR spectroscopy. The double set of signals in I3C CP/MAS spectra indicates that molecules of N'-ethyl-Nz-(3-methy1phenyl)thiourea and N'-ethyl-N2-(4-methyIphenyl)thiourea are crystallographically non-equivalent. N'-Propene-N2-phenylthiourea forms cyclic dimers with two NZ-H. -.S hydrogen bonds, as confirmed recently by x-ray diffraction. The broad vNH maxima at 3175-3295 cm-' in the IR spectra indicate that in other thioureas both N'-H and N2-H protons are involved in hydrogen bonding and that the non-bonded N'-H proton in cyclic dimers of N'-propenethioureas is probably an exception. Semi-empirical AM1 calculations showed that the N2-H proton is more positively charged than the N'-H proton and therefore should be preferentially involved in N2-H. * .S hydrogen bonds. KEY WORDS solid-state I3C CP/MAS NMR; IR; thioureas; hydrogen bonding ' ,C NMR spectra of solid, crystalline N'-alkyl-N'-arylthioureas were recorded by CP/MAS. A spinning speed of about 3-4 kHz was enough to circumvent sidebands and to assign chemical shifts of aliphatic and aromatic