Removal of Duplicates

(original date 2013-2-13) Since last year, I did some work on removing duplicate structures from the database (the spectra were kept, of course, and all assigned to one structure). Just in case somebody wonders what happened so that duplicate structures occured, here is the main reason (the other reason are simple software bugs e. g. in SMILES generation or in the code doing the save to the database): nmrshiftdb2 requires information about which configurations around double bonds are actual E/Z-configurations as drawn and which are unspecified and just drawn randomly in one way (I still think that without this information, real decisions about structure identity cannot be made). In the past, this information was also asked in small rings where actual E/Z-configurations cannot occur. If in one case the bond was declared as "unspecified" and in the other as "as drawn", two entries with different IDs for the same structure were made. A typical example is molecule ID 2505 - this existed twice (the other ID was 20039308, but this has disappeared, really the only case where ID disappear) with the bond from 5 to 6 being considered in Z configuration in one of them, unspecified in the other. These have now been merged and 2505 has two spectra (both 13C here, but many of the merges lead to structures now having 13C and 1H spectra). 90 such merges happened.