Preventing Bonding

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FX ChemStruct uses a complicated algorithm to determine where the "next" element is attached to the existing structure.  Sometimes this can cause problems if you want to leave a "bonding site" unbonded.

 

For example:

 

EDTA

 

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Imagine you are trying to enter this structure into FX ChemStruct.  You might start with one of the N's and move out one of the arms

 

nch2coo

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So far so good.  Now if you attempt to start another arm - by typing a C - things start to go wrong

 

nch2cooc

 

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FX ChemStruct has no way of knowing that you have finished the first arm and attached the C to the remaining bonding site on the O.  Oops!  What we need is a way of telling FX ChemStruct to stop there.  You can do this using the * key.

 

nch2coo*c

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The * has prevented the C from bonding to the O so FX ChemStruct bonds the C to the N instead.

 

To enter EDTA we can use

 

nch2ch2nch2coo*ch2coo*ch2coo*ch2coo*        or        nch2ch2n(ch2coo*)4

 

Note:  There are other possible ways of entering EDTA - but all require the use of the * key.