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4.17.2  What is LogP? 

The hydrophobicity (also known as the lipophilicity) is a very important physicochemical property 

used in different areas of chemistry, medicine, and pharmacology.  It is a very important indicator 

of transport and permeation through membranes, interaction with biological receptors and 

enzymes, toxicity, and biological potency.  

An octanol water partition coefficient, logP, is a measure of compound hydrophobicity; once you 

have obtained reliable logP values for a series of compounds, you are able to estimate many of 

their properties as listed above, provided these properties correlate with logP. 

4.17.3  Description of Algorithm 

The ACD/Labs algorithm performs the following procedures in the course of calculating logP:  

1.  Splits the structure into fragments. 

2.  Searches for identical fragments in the internal databases: 

The database of Fragmental Increments contains well characterized increments for over 

500 different functional groups.  These differ from each other by their chemical structure 

(e.g., amide, carboxy, ester, etc.), attachment to the hydrocarbon skeleton (aliphatic, 

vinylic, or aromatic), cyclization (cyclic or non cyclic), and aromaticity (non aromatic, 

aromatic, or fused aromatic). 

The database of Carbon Atom Increments contains well characterized increments for 

different types of carbons that are not involved in any functional group.  They differ from 

each other by their state of hybridization (sp, sp2, or sp3), number of attached hydrogens, 

branching (primary, secondary, tertiary, or quaternary), cyclization (cyclic or non cyclic), 

and aromaticity (non aromatic, aromatic, or fused aromatic). 

The database of the Intramolecular Interaction Increments contains well characterized 

increments for over 2,000 different types of pair wise group interactions.  They differ from 

each other by the type of the interacting terminal groups (see the differences among 

functional groups above), and the length and type of the fragmental system in between the 

interacting groups (aliphatic, aromatic, and vinylic). 

3.  If some fragments are not found in neither of the above mentioned databases, the program 

estimates their increments (as well as increments of inter fragmental interactions) using 

Secondary Algorithms.   

Lastly, the algorithm estimates the probability of tautomeric and ionic equilibria, calculation error 

and displays the results. 

4.17.3.1  For I Lab: Intranet Edition ACD/LogP Accuracy Extender 

The training capability for logP/logD calculation is improved in version 7.0.  As well, the 

LOGPUSER.CLC file can be created with ACD/LogP Accuracy Extender.  You can further use 

this file to improve the accuracy of logP/logD prediction.  (For more information, refer to Section 

3.6.1.1.) 

ACD/I Lab via ChemSketch  

User's Guide 

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