I Lab Services 

4.25.3  Limitations for Adsorption Coefficient 

The algorithm does not calculate the K

oc

 for the following chemical structures: 

Structures containing atoms other than C, H, O, S, N, and F in possible chemical 

surroundings or structures containing atoms P, Cl, Br, I, Se, Si, Ge, Pb, Sn, As, and B that 

are not within the chemical surroundings shown below (note that A denotes any atom out 

of C, O, S, N, F, or any group listed below

9

):   

A

A

A

A

A

Cl

A 

B

A

Ge

A

P

A

Se

A

10

A

A

A

A

A

A

A

Se

A  

Br

A 

Sn

A

P

A

A

A

A

A

A

A

I

A 

Pb

A

As

A

A

A

Structures containing atoms in non typical valence states (see the Elements Table in the 

ACD/ChemSketch for information on individual atomic valences); 

Structures containing non covalent (co ordination) bonds; and 

Structures containing more than 255 heavy atoms or 10 ionization centers. 

Additionally, the algorithm does not take into account the specific features of different geometric 

isomers, stereomers, conformers, and isotopes.  The algorithm does not correct its prediction for 

long range non covalent bonding, intra molecular shielding, or inter molecular association. 

4.25.4  What is Adsorption Coefficient? 

The organic carbon adsorption coefficient, K

oc

, is crucial for estimating a chemical compound's 

mobility in soil, and the prevalence of leaching from soil.  The adsorption of a compound 

increases with an increase in organic content, clay content, and surface area of soil.  The 

presence of a chemical compound can also be detected in groundwater, and inference can be 

made about its residence time in the soil and the degradation period before reaching the water 

table.  The presence of continuous pores or channels in soil will increase the mobility of a 

chemical compound in the soil. 

The Adsorption Coefficient (K

oc

) may be defined as the ratio of the amount of chemical adsorbed 

per unit weight of organic carbon (oc) in the soil or sediment to the concentration of the chemical 

in solution at equilibrium: 

g

adsorbed / g

organic

carbon

K

oc

g / mL

solution

9

 This group cannot be a part of a cycle unless otherwise stated. 

10

 This fragment can be a part of an aromatic cycle. 

ACD/I Lab via ChemSketch  

User's Guide 

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