### 16.2. Do I need to know how my molecular information was created? 

Conventional methods of representing molecular structure often produce some fuzziness; as a result, you may need to make assumptions about the defaults used by the creator. Examples are:

·         *Are all hydrogen atoms explicit?* 
 If you know they are, then you should run InChI with the DoNotAddH option. This is by far the most powerful way of ensuring that your InChI is likely to be correct. 

·         *Are all charges included in the files?* 
 Sometimes the creation mechanism omits charges on atoms. This can make it very difficult to calculate the correct molecular constitution and the total electron count. 

·         *Are all stereo centers marked?* 
 Many historical data files have no stereochemistry. Many others have partial stereochemistry (e.g. "everyone knows what the stereochemistry of androstane steroids is so we needn't put it in.") 

·         *Is the stereochemistry absolute or relative?* 
 Even if the all the stereocenters are given, the absolute stereochemistry may be unknown or the sample may be racemic. 