A theoretical investigation of the competition between hydrogen bonding and lone pair⋯π interaction in complexes of TNT with NH3

Abstract

A theoretical study of the interactions between 2,4,6-trinitrotoluene (TNT) and ammonia (NH3) has been carried out by means of MP2, DFT, and CCSD(T) methods. Eight stable structures of TNT⋯NH3 complexes were identified at the MP2/6-311++G(d,p) level. Various interactions such as lone pair⋯π interaction (lp⋯π interaction), conventional NH⋯O, CH⋯N, N–H···π hydrogen bonds, and novel noncovalent C⋯N carbon bonding, have been observed in the titled complexes. The competition between hydrogen bonding and lp⋯π interaction in the complexes was studied and discussed. The attractive lp⋯π interactions are observed when the lone pair of NH3 points toward TNT π ring. At the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level, the corresponding BSSE corrected interaction energy (ΔE) is −3.7kcalmol−1. The calculated results also show that the lp⋯π interaction competes successfully with the NH⋯π and NH⋯O hydrogen bonds. The competition between hydrogen bonding and lp⋯π interaction in TNT⋯NH3 complexes plays important role to affect the structures of complexes. However, the conventional CH⋯N hydrogen bond is stronger than the lp⋯π interaction. The complex I merely with CH⋯N hydrogen bond is the most stable structure among eight complexes. The theoretical studies on UV and IR spectra of the TNT⋯NH3 complexes show that the formations of hydrogen bonding and lp⋯π interaction have small effect on the UV spectra but new IR absorption peaks in range of 100–300cm−1 correlated to interactions between TNT and NH3 have been predicted, which may be helpful for the detection of TNT.