Luca Baumer

Residual charges on atoms in organic structures: A new algorithm for their calculation

Abstract A fast algorithm for the evaluation of residual charges in organic structures is presented. Its validity extends over single and isolated multiple bonds. The model considers only atom connectivities as the topological basis and atom electronegativities and covalent radii as physical characteristics; the use of an iterative procedure and well-defined computational rules ensures self consistency for the method which is tested through the calculation of atomic charges in several molecules and through a comparison of results obtained with other methods. The Fortran 77 source code RESCHA.FOR the PC executable RESCHA.EXE, sample input PROST.MOL, and resulting output PROST.OUT are included on disk.

Organic synthesis planning: a new algorithm for strategic bond perception

Abstract A new algorithm which generates breaking suggestion for Organic Synthesis Planning (OSP) is described. A new strategical approach to organic synthesis design has been used. New definition for structural complexity weight, atom complexity distance, molecular centre, Minimal Sets of Strategic Bonds are presented. The need for separate program sections for the strategic part and the transformation model is addressed. Some results are given and comments made to illustrate the algorithm performance.

Organic synthesis planning: An algorithm for selecting strategic bond forming sequences

Abstract An algorithm part of a computer program (Lilith) or convergent retrosynthesis planning is described. It chooses the optimal forming sequence tor a given set of strategic bonds. Its heuristic rules consider complexity distances, steric congestions and ease of cyclization. The procedure used for fast evaluation of approximated congestion at reaction center is outlined. Linkings of the alqorithm with the previous parts and with the general approach of Lilith are emphasized. Applications to natural substance synthesis projects are exemplified.

Residual charges on atoms in organic structures: A new method for the identification of conjugated systems and the evaluation of atomic charge distribution on them

Abstract The extension of a previously described method for the evaluation of atomic charges in organic structures is presented. The application to conjugated and aromatic systems is considered. The identification of the atoms involved in the conjugation and their conjugative distances is afforded by a novel and straightforward method. Merging of the two algorithms for charge calculation is accomplished. The method is tested through calculation of several molecules and results are discussed.

New method for the calculation of bond native polarity using molecular electronic energy

A procedure for the calculation of atomic and molecular electronic energy is described. The calculated energies of some example molecules are compared with either ab initio or semiempirical results. The calculation of electronic energies is used inside a different procedure to evaluate the native polarities of strategic bonds of organic molecules; the corresponding algorithm is described, and some examples of its application are reported. The results are compared with those obtained by a previously described approach and with usual chemical reactivity. Differences and improvements introduced by the present method are discussed.

Ring perception in organic structures: A new algorithm for finding SSSR

Abstract An original algorithm for ring perception in organic chemical structures is presented. It divides rings into two classes to be separately investigated, simplifies the molecular graph and, without finding all possible cycles, efficiently identifies only the SSSR, as required by the synthesis planning program Lilith of which it is a part. Its application to some organic structures and to particular ring systems is reported. An evaluation of speed is included.

Residual charges on atoms in organic structures: Molecules containing charged and backdonating atoms

Abstract The extension of a previously described method for the evaluation of atomic charges in organic structures is presented. The application to structures containing charged atoms is considered. A search for the atoms involved in the initial distribution of the charge is afforded extending a method previously described. Bond orders are changed according to the existence of canonical forms. The problem of backdonating atoms is analyzed and discussed and a possible solution is presented. The method is tested through calculation on several molecules and results are discussed. This program is included on disk in this issue.

The LILITH approach to organic synthesis planning

Abstract The general basis of the LILITH program is outlined. The size of the possible solution space is reduced by enhancing convergence, simplification and ordering. Complexity distance, relevant bond sets and ordering for bond-forming sequences are described. The evaluation of reactivity is the second main aspect in organic synthesis planning. Properties involving the ground state (native bond polarity) and the excited state (group-similar interference) contribute to the prediction of reactivity.

Similar Group Interferences. A General Approach to the Location of Interfering Functionalities.

Abstract The location and evaluation of interfering functionalities are aspects of great importance in the synthesis planning, because the success of a synthesis often depends on the correct management of functionalities involved both in the formation of the strategic bond and in the multiplication of the reactive sites. The present approach introduces a new subdivision of interferences acting either locally (Similar Group Interferences) or generally (Group Environment Interferences), and suggests a solution for the first case. Using a group of molecular descriptors the level of local interference of a functional group is calculated and the possibility to be an alternative reacting site is determined. Electrophilic and nucleophilic situations are separately considered and the complete procedure for the identification of SGIs is described. Example studies are discussed in both simple and complex structures.