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 Post subject: Combinatorial chemistry problemPosted: Tue Jun 04, 2013 9:33 pm

Joined: Mon Mar 30, 2009 5:13 pm
Approximately how many different organic molecules are possible which satisfy the following conditions:

1. Molecular weight no more than 500 Da (g/mol)
2. Comprising any of the elements C, H, N, O, S, P, but no others
3. Must contain at least one carbon (C)
4. Valid chemical structures only, based on common groups

Can anyone think of a good way to calculate or estimate this?

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 Post subject: Re: Combinatorial chemistry problemPosted: Tue Jun 04, 2013 10:06 pm

Joined: Mon Apr 01, 2013 8:27 pm
I sent the question to my former roommate who is doing research in organic chemistry. I'll let you know if he comes up with anything.

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 Post subject: Re: Combinatorial chemistry problemPosted: Wed Jun 05, 2013 7:38 am

Joined: Mon Feb 06, 2006 12:52 am
Wow. There will be many. So many.
I have no idea how many though.

Now the average mass of all of them is 17.7 g/mol
So 500 g/mol is a whole lot. About 28 Atoms if you just assume that all atoms of the molecules have the average mass in every possible combination.
Which is a totally unrealistic!
Since there are 6 different possibilities and you assume that it is possible to put 27 atoms (since one has to be C) or less of the same kind into one molecule
which is totally unrealistic,
you get 6^27= 1 023 490 369 077 470 000 000 possibilities. Note, that all molecules with less then 500 g/mol are not even included!

Of course, I am not saying that the number I just wrote down is in any way even a good guess for the range.
But imagine all the carbo chains with subsitutes and all the different possibilities and all the benzene rings and all those amino chains... Just look outside as you think about this and spot a tree. A plant. A bug. Your skin. The earth. The different colors of flours, food and particles. Man I guess the number might just be higher than the permutations of a Rubik's cube.

Did I say Rubik's cube? Oh were are in the Off Topic section, sorry.

EDIT: I thought again, and I come to a more specific conclusion: About 4. +/- 1. Yes. Pretty sure that's it.

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 Post subject: Re: Combinatorial chemistry problemPosted: Wed Jun 05, 2013 10:35 am

Joined: Wed Mar 15, 2000 9:11 pm
Location: Delft, the Netherlands
In general there is no exact formula for this kind of thing. It's rather complicated, although the
Polya enumeration theorem has been used in some cases to enumerate a set of acyclic molecules. I don't know if it could be used in a case like this, as I haven't looked into it.

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