Subject: SUMMARY 1,3,5-cyclohexatriene

From: Valentine Ananikov <[email-masked]>
Date: Fri, 26 May 2000 18:05:18 +0400

Dear CCL,

Below is my original message and replies I've got. In summary
the following references were suggested:

J. Mol. Struct. (THEOCHEM) 1994, 398-399 155-167
J.Am.Chem.Soc., 1996, 118: (31) 7381-7385
Chem.Ber., 1994, 127: (9) 1765-1779
J.Am.Chem.Soc., 1993, 115: (23) 10952-10957
J.Am.Chem.Soc., 1992, 114: (21) 8263-8268

and I thank to Xavier Assfeld, Chaitanya Wannere, E. Lewars,
Adam Matzger, and Alan Shusterman for the contribution!

best regards, Valentin.

----------
   Dear List Members,

Does anybody have an information about predicted structure and 
stability for 1,3,5-cyclohexatriene?

I mean a six-membered ring with alternating single and double
C-C bonds, but without aromatic pi-electrons delocalization due
to non-planar conformation (i.e. non-planar benzene isomer).
Would such structure exist in principle?

Thanks!  Valentin.
-----------

+++++++++++
Hi,

have a look at:
"a different story of benzene"
S. Shaik, A. Shurki, D. Danovich, P. Hiberty
J. Mol. Struct. (THEOCHEM) 398-399 (1997) 155-167.

Hope this helps.

                                      ...Xav

Ast. Pr. Xavier Assfeld      
+++++++++++++

+++++++++++++
Hi Valentine, 

This is the geometry of the 1,3,5-cyclohexatriene that I got from our
archive. 

C 1.2263000 0.6748000 0.0000000
C 1.2263000 -0.6748000 -0.0000001
C -1.1975440 0.7246069 0.0000001
C -0.0287562 1.3994070 -0.0000001
C -0.0287562 -1.3994070 0.0000001
C -1.1975440 -0.7246069 0.0000000
H 2.1548711 1.2347514 -0.0000001
H 2.1548711 -1.2347514 -0.0000000
H -2.1467617 1.2487973 0.0000000
H -0.0081096 2.4835488 -0.0000001
H -0.0081096 -2.4835488 0.0000001
H -2.1467617 -1.2487973 0.0000001

1.     Johnson RP, Daoust KJ
       Electrocyclic ring opening modes of Dewar benzenes: Ab initio
predictions for Mobius benzene and trans-Dewar benzene as new C6H6
isomers
       J AM CHEM SOC 118: (31) 7381-7385 AUG 7 1996 

2.     ROTH WR, HOPF H, HORN C
       THE ENERGY WELL OF DIRADICALS .5. 1,3,5-CYCLOHEXATRIENE-1,4-DIYL
AND 2,4-CYCLOHEXADIENE-1,4-DIYL
       CHEM BER 127: (9) 1765-1779 SEP 1994 

3.     GILLARD JR, NEWLANDS MJ, BRIDSON JN, et al.
       PI-FACIAL STEREOSELECTIVITY IN THE DIELS-ALDER REACTIONS OF
BENZENE
OXIDES
       CAN J CHEM 69: (9) 1337-1343 SEP 1991 

4.     KREITER CG, MICHELS E, KURZ H
PHOTOCHEMICAL-REACTIONS OF TRANSITION-METAL OLEFIN COMPLEXES .4. 
PHOTOCHEMICAL CYCLOADDITION OF CYCLIC DIENES ON 
TRICARBONYL-ETA-6-1,3,5-CYCLOHEXATRIENE-CHROMIUM(O)
       J ORGANOMET CHEM 232: (3) 249-260 1982 

These are the references that I know of, additionally the back
references
included in this paper might help you in tracing what you are exactly
looking for.

Best Wishes,
Chait

Chaitanya S. Wannere
++++++++++++

++++++++++++
Hello,

The answer to your question (below), phrased as a general problem, is
not as quite simple as one may think. The conventional response would
be
that cyclohexatrine structures are resonance structures (canonical
structures) contributing to the actual structure, a resonance hybrid,
and so can't have any real existence: they are just bond-stretching
vibrational extremes with benzene vibrating about a geometry of mean
(average) hexagonal symmetry (think of a Morse curve). the energy of
the
purely hypothetical 1,3,5-cyclohexatriene has been evaluted in
connection with its use as areference molecule in assigning a resonance
energy to benzene (e.g. work by M. J. S. Dewar--treated in some org
chem
textbooks). 

 So much for benzene, but for cyclobutadiene the alternating C-C/C=C
structures are real: the potential energy surface has two minima
separated by a transition state. Predicting the results for simple
polyene cases requires, usually, only knowing about aromaticity and
antiaromaticity and the Hueckel rule, but _generally_ distinguishing
between resonance (as in benzene) and valence tautomerism (as in
cyclobutadiene) requires actual calculation. The problem of "the thin
line" (quoting Paquette) between the two was discussedby L. Paquette in
J Am Chem Soc in a paper on homoaromaticity about 10-15 years ago.

E. Lewars
++++++++++

++++++++++
These references will get you started:

THE ROLE OF DELOCALIZATION IN BENZENE
GLENDENING ED, FAUST R, STREITWIESER A, VOLLHARDT KPC, WEINHOLD F
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 
115: (23) 10952-10957 NOV 17 1993

ABINITIO STUDY OF SIGMA-EFFECTS AND PI-EFFECTS IN BENZENES FUSED TO
4-MEMBERED RINGS - REHYBRIDIZATION, DELOCALIZATION, AND ANTIAROMATICITY
FAUST R, GLENDENING ED, STREITWIESER A, VOLLHARDT KPC
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 
114: (21) 8263-8268 OCT 7 1992

You should also check science citation index for opposing viewpoints.

                                                Adam Matzger
++++++++++

++++++++++
Dear Valentin,
        Your question is almost impossible to answer because
1,3,5-cyclohexatriene does not exist, and all quantum calculations will
allow electrons to delocalize.
        There are some ways to restrict the degree of localization
during the calculation, but calling any of the resulting molecules
"1,3,5-cyclohexatriene" is very arbitrary (and different localization
schemes will give you different results).
        I tried using Jaguar to do a GVB-PP/6-31G** calculation on
"1,3,5-cyclohexatriene". There were 9 GVB electron pairs in my
calculation, the 6 CC sigma bond pairs and the 3 CC pi bond pairs. The
other electron pairs were all treated using Hartree-Fock-type orbitals.
The CC bond distances finished at 1.367 and 1.458 Å, so that is one
estimate of the structure of this fictional molecule.

-Alan
====
Alan Shusterman
+++++++++++

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