Subject: Re: CCL:X ray structure needed

From: Jacco van de Streek <[email-masked]>
Date: Wed, 11 Sep 2002 10:14:04 +0100

Juan Alexander Padron Garcia wrote:
> 
> Dear List:
> 
> I need the X ray structure of several compounds (octene, 2
> methyl-octanal and nonanal) to compare structure optimizacion methods.
> Does any could help me?

Hi,

I used to do calculations on crystal structures of long-chain compounds
(n-alkanes) for my PhD, and I soon learned that it its very hard to obtain
suitable single crystals / powder data. As a result, not many crystal structures
of long-chain compounds have been solved.

If the crystal structures you are looking for have been solved, they should be
in the Cambridge Structural Database, which is maintained by the institute I now
work for. I searched for the following two fragments:

   CH2-CH2-CH2-CH2-CH2-HC=O

and

  CH2/3-CH2-CH=CH-CH2-CH2/3

There were no hits for the first one. The second fragment returned crystal
structures for alkenoic acids and the like, e.g. cis-13-docosenoic acid, oleic
acid (both cis) and 1,2,3-tris(trans-9-octadecenoyl)glycerol (trans).

Assuming that you need the crystal structures to check the molecular geometries
rather than the crystal packings, these molecules should be a start. Be aware of
the effect the crystal packing has on the conformation, though: there is no
single "correct" solid-state conformation for molecules this flexible.

If you do not have access to the Cambridge Structural Database, please contact
mailto:[email-masked] for information on how to obtain the co-ordinates
of a specific crystal structure from the Cambridge Structural Database.

Jacco.
-- 
Jacco van de Streek
Research Scientist
Cambridge Crystallographic Data Centre
Cambridge
United Kingdom