Hindawi Publishing Corporation Advances in Physical Chemistry Volume 2012, Article ID 304686, 11 pages doi:10.1155/2012/304686 Research Article Predicting Heats of Explosion of Nitroaromatic Compounds through NBO Charges and 15 N NMR Chemical Shifts of Nitro Groups Ricardo Infante-Castillo 1 and Samuel P. Hern´ andez-Rivera 2 1 Department of Physics and Chemistry, University of Puerto Rico, Arecibo Campus, P.O. Box 8152, Arecibo, PR 08152-00613, USA 2 ALERT-DHS Center of Excellence/Center for Chemical Sensors Development, University of Puerto Rico, Mayag¨ uez Campus, P.O. Box 9000, Mayaguez, PR 00681-9000, USA Correspondence should be addressed to Ricardo Infante-Castillo, ricinfante@gmail.com and Samuel P. Hern´ andez-Rivera, samuel.hernandez3@upr.edu Received 23 March 2012; Revised 12 June 2012; Accepted 12 June 2012 Academic Editor: Michael D. Sevilla Copyright © 2012 R. Infante-Castillo and S. P. Hern´ andez-Rivera. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This work presents a new quantitative model to predict the heat of explosion of nitroaromatic compounds using the natural bond orbital (NBO) charge and 15 N NMR chemical shifts of the nitro groups ( 15 N Nitro ) as structural parameters. The values of the heat of explosion predicted for 21 nitroaromatic compounds using the model described here were compared with experimental data. The prediction ability of the model was assessed by the leave-one-out cross-validation method. The cross-validation results show that the model is significant and stable and that the predicted accuracy is within 0.146 MJ kg −1 , with an overall root mean squared error of prediction (RMSEP) below 0.183 MJ kg −1 . Strong correlations were observed between the heat of explosion and the charges (R 2 = 0.9533) and 15 N NMR chemical shifts (R 2 = 0.9531) of the studied compounds. In addition, the dependence of the heat of explosion on the presence of activating or deactivating groups of nitroaromatic explosives was analyzed. All calculations, including optimizations, NBO charges, and 15 N Nitro NMR chemical shifts analyses, were performed using density functional theory (DFT) and a 6-311+G(2d,p) basis set. Based on these results, this practical quantitative model can be used as a tool in the design and development of highly energetic materials (HEM) based on nitroaromatic compounds. 1. Introduction Aromatic molecules with nitro groups are an important class of highly energetic materials (HEM). One of the most important thermodynamic properties that determine the performance of these explosives and propellants is the heat of explosion (HE). The HE is the quantity of heat liberated when an HEM undergoes detonation as a high explosive or deflagration as a low explosive. The processes of detonation and deflagration occur even in the absence of external oxygen or air because HEM contain oxygen themselves. The HE can be theoretically calculated [1] and experimentally determined [2]. The calculated value is determined by the difference between the energies of formation of the explosive components and the energies of formation of the explosion products. Experimentally, the HE is determined using a calorimetric bomb. The sample quantity is usually chosen to obtain a loading density of 0.1 g/cm 3 . If a powder will not explode (compounds with heat of explosion lower than 800 cal/g), a “hot” powder with a known heat of explosion is added. Thus, the HE of the sample powder can be calculated from the mixture. The calorimetric values used in this work are based on liquid H 2 O as a reaction product. Predicting the performance and thermochemical prop- erties of energetic materials from a given molecular structure with or without using experimental measurements is critical in the research and development of explosives. Several relationships have been found that relate explosive charac- teristics with measured and predicted molecular properties. The relationship between thermal [3], impact [4, 5], and