Premium
An Ab initio study on the conformations of protonated, neutral, and deprotonated amidine
Author(s) -
Zielinski Theresa Julia,
Peterson Michael R.,
Csizmadia Imre G.,
Rein Robert
Publication year - 1982
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540030111
Subject(s) - amidine , protonation , chemistry , deprotonation , ab initio , computational chemistry , ab initio quantum chemistry methods , valence (chemistry) , molecular orbital , transition state , gaussian orbital , crystallography , stereochemistry , molecule , catalysis , organic chemistry , ion
Abstract Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(NH)NH 2 ], 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 –NH 2 site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HNCN cis and trans isomers, respectively, while all the stable HC(NH 2 ) 2 + and HC(NH) 2 − species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C—N single‐bond rotation in HC(NH)NH 3 + , the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HNCN isomers, respectively.