Gas-phase acidity of urea

✍ Scribed by Ma, Shuguang; Wang, Feng; Cooks, R. Graham

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 273 KB
• Volume: 33
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(1998100)33:10<943::aid-jms703>3.0.co;2-b

✦ Synopsis

The kinetic method was applied to the estimation of the gas-phase acidity of urea by generating proton-bound dimeric anions comprised of urea and various reference compounds using negative ion desorption chemical ionization and examining their dissociation upon collision in a triple quadrupole mass spectrometer. The individual mass-selected dimers fragment to yield the two deprotonated anions as the only product ions. From the relative product ion abundances, is determined to be 1513.8 » 12 kJ mol-1, is 85.8 » 8 J mol-1 K-1 and DH acid DS acid is estimated to be 1488.2 » 14 kJ mol-1 at 298 K by using where the DG acid DG acid = DH acid Ô TDS acid , DH acid and values are determined directly from the kinetic method plots. The experimental value is in good DS acid DH acid agreement with a value of 1520.5 kJ mol-1 obtained from G2 molecular orbital calculations. 1998 John Wiley ( & Sons, Ltd.