structural formula versus molecular formula

[Nikkinotgill]

Hi All

 

Is there a way of working out structural formula from the molecular formula, or is it a bit of trial and error until all the bonds satisfied? At the moment I am trying out different variations until I get the one that has all the correct number of bonds, but I feel like this can't be how other people do it!

 

For example - take Valine: how would you know the structural formula from C5H11NO2 (other than googling it obviously)

 

Thanks

[hypervalent_iodine]

You can't get much structural information beyond what's in the compound and double bond equivalents from a molecular formula.

[Nikkinotgill]

Thanks... ll go back to drawing out possibilities till I get the right one then haha.

[John Cuthber]

You might not get as far as you think

dimethyl ether

http://en.wikipedia.org/wiki/Dimethyl_ether

and ethanol

http://en.wikipedia.org/wiki/Ethanol

have the same molecular formula

C2H6O

 

Compounds that have the same molecular formulae but different structures are called isomers

http://en.wikipedia.org/wiki/Isomer

[hypervalent_iodine]

As John Cuthber has said, you really can't justify the structure from just the molecular formula. Molecular formula can represent many different chemical structures and you have no way of knowing the correct one for your question without much more info. Is there any reason you are trying to do this?

[Enthalpy]

http://webbook.nist.gov/cgi/formula/C5H11NO2

Nist lists 38 compounds and doesn't claim to be exhaustive

 

http://en.wikipedia.org/wiki/C5H11NO2

Wiki has only 5