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An Ab initio study on the conformations of protonated, neutral, and deprotonated amidine

✍ Scribed by Theresa Julia Zielinski; Michael R. Peterson; Imre G. Csizmadia; Robert Rein

Publisher
John Wiley and Sons
Year
1982
Tongue
English
Weight
422 KB
Volume
3
Category
Article
ISSN
0192-8651

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✦ Synopsis

Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(=NH)NHz], using the 3-21G split valence basis set. The states of eight stable species, eight transition states, and four higher-order saddle points have been determined by complete geometry optimization utilizing analytic energy gradient techniques. Protonation at the amidine =NH is preferred over the -NHz site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HN=CN cis and trans isomers, respectively, while all the stable HC(NH2): and HC(NH), species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C-N single-bond rotation in HC(=NH)NHg, the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HN=CN isomers, respectively.

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