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Gas‐phase acidity of urea
Author(s) -
Ma Shuguang,
Wang Feng,
Cooks R. Graham
Publication year - 1998
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(1998100)33:10<943::aid-jms703>3.0.co;2-b
Subject(s) - chemistry , mass spectrometry , deprotonation , ion , dissociation (chemistry) , kinetic energy , quadrupole mass analyzer , analytical chemistry (journal) , ionization , urea , yield (engineering) , gas phase , chemical ionization , electron ionization , organic chemistry , chromatography , thermodynamics , physics , quantum mechanics
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, Δ H acid is determined to be 1513.8±12 kJ mol ‐1 , Δ S acid is 85.8±8 J mol ‐1 K ‐1 and Δ G acid is estimated to be 1488.2±14 kJ mol ‐1 at 298 K by using Δ G acid =Δ H acid ‐TΔ S acid , where the Δ H acid and Δ S acid values are determined directly from the kinetic method plots. The experimental Δ H acid value is in good agreement with a value of 1520.5 kJ mol ‐1 obtained from G2 molecular orbital calculations. © 1998 John Wiley & Sons, Ltd.