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We have investigated the use of the average local ionization energy, I[combining overline](S)(r), as a means for rapidly predicting the relative reactivities of different sites on two model graphene surfaces toward the successive addition of one, two, and three hydrogen or fluorine atoms. The I[combining overline](S)(r) results were compared with directly computed interaction energies, at the B3LYP/6-311G(d,p) level. I[combining overline](S)(r) correctly predicts that the edges of graphene sheets are more reactive than the interior portions. It shows that added hydrogens activate the adjoining (ortho) sites and deactivate those that are separated by one site (meta). Overall, I[combining overline](S)(r) is effective for rapidly (single calculations) estimating the relative site reactivities of these large systems, although it reflects only the system prior to an interaction and cannot take into account postinteraction factors, e.g., structural distortion.

We have extended an earlier crystallographic/ computational study which revealed an exceptionally short C-Cl bond in chlorotrinitromethane, Cl-C(NO 2 ) 3 . We show that the C-Cl bond length progressively decreases when NO 2 groups are introduced into chloromethane. This is attributed to intramolecular attractive interactions between the chlorine and the closest NO 2 oxygens. Computed electrostatic potentials on molecular surfaces support this interpretation, as well as the N-O interactions between neighboring NO 2 groups that help to determine the molecular conformations. The calculated C-Cl bond energies decrease as the NO 2 groups are added, which is expected, but means that the usual inverse relationship between bond energy and bond length is not being obeyed. For purposes of comparison, the computational analyses, which were primarily at the B3PW91/6-311G(3d,2p) level, were also carried out for the corresponding chlorocyanomethanes and chlorofluoromethanes. These do not show anomalously short C-Cl bond distances.

In a continuing effort to further explore the use of the average local ionization energy [Formula: see text] as a computational tool, we have investigated how well [Formula: see text] computed on molecular surfaces serves as a predictive tool for identifying the sites of the more reactive electrons in several nonplanar defect-containing model graphene systems, each containing one or more pentagons. They include corannulene (C20H10), two inverse Stone-Thrower-Wales defect-containing structures C26H12 and C42H16, and a nanotube cap model C22H6, whose end is formed by three fused pentagons. Coronene (C24H12) has been included as a reference planar defect-free graphene model. We have optimized the structures of these systems as well as several monohydrogenated derivatives at the B3PW91/6-31G* level, and have computed their I(r) on molecular surfaces corresponding to the 0.001 au, 0.003 au and 0.005 au contours of the electronic density. We find that (1) the convex sides of the interior carbons of the nonplanar models are more reactive than the concave sides, and (2) the magnitudes of the lowest I(r) surface minima (the I S, min) correlate well with the interaction energies for hydrogenation at these sites. These I S, min values decrease in magnitude as the nonplanarity of the site increases, consistent with earlier studies. A practical benefit of the use of I(r) is that a single calculation suffices to characterize the numerous sites on a large molecular system, such as graphene and defect-containing graphene models.

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