MAR 3 1 1965

1931 Golden Gate
San Francisco, Calif. 94115
March 30, 1965

Professor Joshua Lederberg
Stanford University School of Medicine
Falo Alto, California

Dear Professor Lederberg:

Thanks very much for your letter of March 26, the reprint of your very
interesting paper and the two pages of Figures 1-7. To answer your postscript
first, Ruie 43 doesn't apply to 1CA4A and 1CA4B because they have no crossed
bonds or shared bridges. Rule 30, however, gives identical notations for all
four diagrams, 1043, 1O0A4A, 10A4B and 1046. The locant paths are as follows:

 

f d NS cee sane rem od c nr ee “i
I ™ \e a! i dine j | h-——i.
er : ‘ : Ne ro f \ I MS
. . : i i ! f : j ‘
Pod Oj. | £ | bee ON
p@- 4S Ae | fo ga “dj
fon ny. bh alg NO A
Be Cee aL b Sh Sf
10A3 LOAKA 10448 10A6

The notation is L634 By C4 D3 4ABCD JTJ for any of these representations
of this structure. Wiswesser.has shown this identity in another way by citing
the pairs of connected locants that are not alphabetically consecutive. Here
they are af, ag, bh, ci, dj, ej, and are identical for each representation.

This locant path produces the lowest sum for the fusion locants-—Wiswesser's
original conjecture--and this is still the most used consideration by far of Rule 30.
The locant path is most easily found in 10A6 where the ring atoms that are shared
by three cited rings (the multicyclic points) all appear in the interior of the
planar representation and not in the peripheral uncited six-membered ring. Typically,
the planar representation in which the peripheral. ring is as large as possible is
easiest to encode in this way. I have devoted considerable discussion to these
transformations of altemate representations in the revision of the Wiswesser manual
which I'm writing.

The largest effort of which I'm aware for converting Wiswesser notations to
other forms is that of Drs. Franc Landee and Carl Bowman of The Vow Chemical Co.
Since I'm their consultant I suppose I must be a bit careful about what I say,
but they made public considerable information about their work at the American
Chemical Society meeting in Philadelphia in April of last year. It has not been
published, howéver. Among other things they have developed algorithms for con-
verting the notaticn to atom connectivity tables and I believe they can manipulate
these in various ways. I expect to see Dr. Bowman next week at the Detroit
meeting of the 4merican Chemical Society and perhaps after that I can answer
your question in more detail.

I'd like very much to visit your computational system open house on April 19.
I'm also looking for ard with great interest to hearing your talk at the Berkeley
ACS maeting in April.
Sincerely,  ,
a Piya 7 owes
meres, Saath
Professor of Chemistry
Mills College

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