MOPAC-derived descriptors

Summary

MOPAC (Molecular Orbital PACkage) is a semi-empirical quantum chemistry = program by James Stewart.

Theo= ry

MOPAC is a general-purpose semi-empirical molecular orbital package for = the study of molecular structures and reactions. For details on MOPAC, see&= nbsp;its manual and website of Stew= art Computational Chemistry. OCHEM uses version 7.1 of MOPAC, which is = still open source (later version are commercial).

Descriptors

OCHEM descriptors are calculated using the mopac@home project.

MOPAC-derived descriptors include both per-molecule descriptors (molecul= ar descriptors) and per-atom descriptors (atomic descriptors).

Molecular descriptors

A block of basic descriptors is calculated. These include T= otalEnergy Sum of the electronic and nuclear (core-core) ener= gies.
ElectronicEnergy Electronic energy.
<= strong>CoreRepulsion Nuclear energy (core-core repulsion.
FinalHeat The final heat of formation.
IonisationPotential The smallest energy required to remove a= n electron.
HomoEnergy The energy of the highest= occupied molecular orbital.
LumoEnergy The ener= gy of the lowest unoccupied molecular orbital.
DipolPointCharg= e Molecular dipole.
DipolHybrid Mo= lecular dipole.
DipolSum Molecular dipole.
= ElectronNuclear
ElectronElectron
ResonanceEnergy
ExchangeE= nergy
ElectronElectronRepulsion <= br />ElectronNuclearAttraction
NuclearN= uclearRepulsion
TotalElectrostaticInteraction
PrincipalMomentsInertia Principal = components as PrincipalMomentsInertiaA, PrincipalMomentsInertiaB, and Princ= ipalMomentsInertiaC .

Atomic descriptors

Atomic descriptors are grouped into net atomic charges and frontier elec= tron theory descriptors. The latter include

Electrophilic frontier electron density
Nu= cleophilic frontier electron density
Electrophilic su= perdelocalizability
Nucleophilic superdelocalizabilit= y
Radial superdelocalizability
= Atom self-polarizability

Frontier electron theory descriptors, in particular electrophilic superd= elocalisability, have been successfully used to model acid dissociation con= stants (Tehan et al., 2002).

Opt= ions

Both molecular and atomic descriptors offer the option use = stereochemistry --

For atomic descriptors, the schema determines= for which atoms the descriptors are computed. The atom (called the center = atom) is usually determined by an obligatory property, e.g., as in acid dis= sociation constants (pKa).

= References

MOPAC

Kenichi Fukui, Teijiro Yonezawa, Chikayoshi Nagata: Theory of Substitut= ion in Conjugated Molecules, Bulletin of the Chemical Society of Japan 27(7= ): 423-427, Chemical Society of Japan, 1954. Frontier electron the= ory

Benjamin Tehan, Edward Lloyd, Margaret Wong, Will Pitt, John Montana, D= avid Manallack, Emanuela Gancia: Estimation of pKa Using Semiempirical Mole= cular Orbital Methods. Part 1: Application to Phenols and Carboxylic Acids,= Quantitative Structure-Activity Relationships 21(5): 457-472, Wiley, 2002.=

Benjamin Tehan, Edward Lloyd, Margaret Wong, Will Pitt, Emanuela Gancia= , David Manallack: Estimation of pKa Using Semiempirical Molecular Orbital = Methods. Part 2: Application to Amines, Anilines and Various Nitrogen Conta= ining Heterocyclic Compounds, Quantitative Structure-Activity Relationships= 21(5):473-485}, Wiley, 2002.