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From: toukie@zui.unizh.ch (Hr Dr. S. Shapiro)
Message-Id: <9607050707.AA59600@rzurs3.unizh.ch>
Subject: More re MOPAC IR
To: chemistry@www.ccl.net
Date: Fri, 5 Jul 1996 09:07:18 +0200 (MEST)
Cc: chminf-l@iubvm.ucs.indiana.edu
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Dear Colleagues;

     A few days ago I posted a query about how to implement MOPAC for the gene-
ration of IR spectra.  I thank the handful of people who took the time and ef-
fort to respond.  In a nutshell, one simply has to add the keyword FORCE, and
a vibrational analysis will be added to the MOPAC output.  (n.b.: In my imple-
mentation of MOPAC 6.0, at least, the keywords FORCE and EF seem to be incompat-
ible.  Does anyone know why that might be?)   One responder mentioned a very
nice programme by Dr. J. Gosper of Brunel University (U. K.) which visualises
the output structure from a MOPAC .out file and which can animate one vibration-
al frequency at a time.  Unfortunately, I do not believe that there yet exists
a programme that will regenerate an IR spectrum as such from the output of a
MOPAC "FORCE" calculation.  (If I am wrong, kidly correct me.)

     As a result of the responses received, I was able to undertake an intelli-
gent search through the local science libraries, and found a particularly use-
ful article:

     SEEGER, D. M., KORZENIEWSKI, C., and KOWALCHYK, W., Evaluation of
     vibrational force fields derived by using semiempirical and ab
     initio methods.  J. Phys. Chem. 95: 6871-6879.

which lists experimental, semiempirical, and ab initio force constants and fre-
quencies for a variety of molecules, as well as recommended sacling factors for
different types of vibrations calculated using the MNDO, AM1, and PM3 parametri-
sations.  One of the responders mentioned that a Dr. Radom (Leo Radom?) has pub-
lished, or has in press, an article further detailing vibrational frequency
scaling factors for MOPAC- and ab initio-calculated molecular vibrational fre-
quencies.  However, I have been unavble to locate such an article.  Does anyone
out there know about this paper?  If so, kindly post details.

     I now wish to follow up my original query about MOPAC and IR with these
two questions:

     (i) The article cited above by Seeger et al. calculated MNDO, AM1, and PM3
scaling factors for hydroxyl O -- H stretches based only upon water.  I am par-
ticularly interested in a scaling factor for hydroxyl O -- H stretches in phenol
and phenolic-type molecules,  both  simple (cresols, xylenols, methoxyphenols)
and more complex (terpenoids, oestrogens, &c.).  Has anyone seen an article in
which a scaling factor for phenolic O -- H stretches is provided?

    (ii) In connection with the above, I am seeking values for phenolic O -- H
stretching frequencies with reference to particular orientations of the phenolic
hydroxy moieties vis-a'-vis the rest of the molecule.  For example, in an old
paper by Simonyi et al [Tetrah. Lett. (19): 1631-1632 (1975), the authors sug-
gest that for 2,6-di-isopropylphenol the O -- H peak at 3641 cm-1 corresponds
to the structure in which the hydroxy moiety is captured between the two methyls
of the isopropyl unit, whereas the O -- H stretch at 3619 cm-1 is due to "a"
conformation in which the hydroxy moiety is _not_ captured between a pair of
isopropyl methyl units.  Can anyone provide me with additional, especially more
recent, references providing experimental phenolic O -- H stretch frequencies as
a function of phenolic conformation?

     Thanks in advance to all responders.


With kindest regards,

(Dr.) S. Shapiro
Inst. f. orale Mikrobiol. u. allg. Immunol.
Zent. f. Zahn-, Mund- u. Kieferheilkd. der Univ. ZH
Plattenstr. 11
Postfach
CH-8028 ZH 7

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