Ozonization of the sidewalls of single-wall carbon nanotubes (SWNT) has been investigated by means of 2-layered ONIOM(B3LYP/6-31G*:AM1) calculations. The theoretical calculations reveal that the 1,3-dipolar cycloaddition (1,3-DC) of ozone (O 3 ) onto the sidewalls of a (5,5) carbon nanotube is site-selective and facile with a small activation barrier of 1.4 kcal/mol. The desorption of ozone from the thus-formed ozonide was found to be favorable over the decomposition process that gives rise to epoxy adduct and O 2 upon thermal activation. This work implies the possibility of functionalizing the sidewalls of SWNTs by means of 1,3dipolar cycloadditions of 1,3-dipolar molecules.

The viability of 1,3-dipolar cycloadditions of a series of 1,3-dipolar molecules (azomethine ylide, ozone, nitrone, nitrile imine, nitrile ylide, nitrile oxide, diazomethane, and methyl azide) onto the sidewalls of carbon nanotubes has been assessed theoretically by means of a two-layered ONIOM approach. The theoretical calculations predict the following: (i) other than the 18-valence-electron azomethine ylide and ozone, the 16-valence-electron nitrile ylide and nitrile imine are the best candidates for experimentalists to try; (ii) upon 1,3-dipolar cycloaddition, a 1,3-diople molecule is di-sigma-bonded to a pair of carbon atoms on the sidewall of SWNT, forming a five-membered ring surface species; (iii) the as-formed 1,3-dipole-SWNT bonding is much weaker than that in the products of the molecular 1,3-DC reactions and can be plausibly broken by heating at elevated temperatures; (iv) the sidewalls of the armchair (n,n) SWNTs (n = 5-10) are subject to the 1,3-DCs of ozone and azomethine ylides; (v) both the 1,3-DC reactivity and retro-1,3-DC reactivity are moderately dependent on the diameters of SWNTs, implying the feasibility of making use of the heterogeneous 1,3-DC chemistry to purify and separate SWNTs diameter-specifically.

The chemisorption and decomposition of thiophene (C 4 H 4 S) and furan (C 4 H 4 O) on the reconstructed Si(100)-2 × 1 surface has been investigated by means of the hybrid density functional (B3LYP) method in combination with a cluster model approach. Two chemisorption mechanisms, i.e., [4 + 2] and [2 + 2] cycloadditions of C 4 H 4 X (X ) S,O) onto a surface dimer site, have been considered comparatively. The calculations revealed that the former process is barrierless and favorable over the latter, which requires a small activation energy (2.6 kcal/mol for thiophene and 1.2 kcal/mol for furan). The di-σ bonded surface species formed by [4 + 2] cycloaddition-type chemisorption can either undergo further [2 + 2] cycloaddition with a neighboring SidSi dimer site, giving rise to a tetra-σ bonded surface species, or undergo deoxygenation (desulfurization) by transferring the heteroatom to a neighboring SidSi dimer site, leading to a six-member ring metallocyclic C 4 H 4 Si 2 surface species. The latter process was found to be slightly more favorable than the former, especially in the case of thiophene.