Ferreira M. M. C., Kiralj R., Vencato I., "A Study of 4-(E)-Amino-3[(E)-nitrophenylazo]-3-penten-2-one and Other Related Azoenaminones in Crystalline State". Caxambu, MG, 23-26/11/2003: 12° Simpósio Brasileiro de Química Teórica (XII SBQT) [12th Brazilian Symposium of Theoretical Chemistry], Livro de Resumos [Book of Abstracts], (2003) P148. Poster P148.

A STUDY OF 4-(E)-AMINO-3-[(E)-4-NITROPHENYLAZO]-3-
PENTEN-2-ONE AND OTHER RELATED AZOENAMINONES IN
CRYSTALLINE STATE

Márcia M. C. Ferreira (PQ),¹ Rudolf Kiralj (PQ),¹ Ivo Vencato (PQ).²
marcia@iqm.unicamp.br
¹Instituto de Química - UNICAMP, Campinas SP, 13084-971 Brazil. ²Instituto de Física - UFG,
Goiânia GO, 74001-970, Brazil.

Palavras-Chaves: ab initio, molecular and crystal structure, chemometrics

              Azoenaminones are compounds  with  potential  nonlinear optical properties  [1].  They
exist as azoenamine/hidrazimino tautomeric mixtures  in solution  (Scheme).   There are  only  a
few structural analyses of 4-nitrophenylazoenaminones and related compounds [2-4],  which do
not provide a  clear picture  of  tautomeric composition of these compounds  in  crystalline state.
             This     is     the     reason     to     study     more     profoundly     the     nature     of     4-
nitrophenylazoenaminones, and particularly of 4-(E)-amino-3-[(E)-4-nitrophenylazo]-3-penten-2-
one by  ab initio  (B3LYP 6-31G**)  methods in free and complexed state,  by making  structural
comparison of related crystal structures retrieved from  the Cambridge Structural Database, and
by  chemometric  analysis  on  molecular  and  crystal  structure  parameters  for  the  compared
phenylazoenaminones.
             The  title and other similar compounds  in  free  state  represent  planar  heteroaromatic
systems  where  tautomerism  is  coupled  with  intrinsic  p-electron  delocalization   (inside  the
nitrobenzene   and   azoenamine   fragments,   and   between  them  and  the  keto  group)  and
intramolecular hydrogen bonds  (Scheme). Based on calculated and experimental bond  lengths
and bond orders,  the  compounds  do not  show  the  same  tautomeric character  in  crystalline
state.   N-N   bond  length  seems  to  be  a  reliable  parameter  for  monitoring   the  p-electron
delocalization  and aromaticity change due to electron  withdrawal/donation  by  substituents on
phenyl  and/or  enamine fragment.   Intermolecular  hydrogen  bonds,   dipole-dipole  and  other
intermolecular interactions in crystal affect molecular geometry,   particularly planarity,  and  are
partially responsible for crystal packing. Some electronic and steric molecular properties  exhibit
qualitative  or  quantitative  relationship  with  crystal   packing  properties   like  crystal  density,
coordination number,   average atomic volume,   and ability to form hydrogen bond networks or
p…p  stacks.  Molecular structure of an azoenaminone  in  crystal  is  mainly located close  to a
delocalized tautomer,  what  does not  always provide reliable experimental determination  of its
tautomeric  composition in solid state. (FAPESP and CNPq)
 



Scheme. Tautomeric/resonance forms of the title compound in crystalline state

[1] L. J. O. Figueiredo, C. Kascheres, J. Org. Chem. 62 (1997) 1164.
[2] B. L. Rodrigues et al., Acta Cryst. C52 (1996) 705.
[3] V. Kettmann et al., Acta Cryst. C57 (2001) 737.
[4] P. Šimunek et al., J. Mol. Struct. 642 (2002) 41.