ChemInform Abstract: Electrostatic Potentials and Relative Bond Strengths of Some Nitro‐ and Nitrosoacetylene Derivatives

Abstract

Abstract : A computational analysis of the structures and properties of a group of substituted acetylenes has been carried out by means of an ab initio self-consistent-field molecular orbital procedure (GAUSSIAN 82). The molecules studied were acetylene, its singly and doubly substituted nitro and nitroso derivatives, methylnitroacetylene, and aminonitroacetylene. The properties computed were the molecular electrostatic potentials and the bond orders, used as measures of relative bond strengths. Among the interesting structural features found for these molecules are a slight nonlinearity of the mono- and dinitrosoacetylene and the fact that the two substituents in dinitro- and dinitrosoacetylene are not coplanar but rather lie in perpendicular planes. The presence of nitrile is observed to strengthen the carbon triple bond carbon, whereas nitrous oxide substitution weakens it. The combination of nitrogen dioxide and NH2 (a strong electron donor) has an overall weakening effect, relative to acetylene. The carbon nitrogen dioxide bonds are found to be stronger than the nitrile bonds. The electrostatic potential analyses show that the introduction of NO2 completely eliminates the negative regions associated with the triple bond, thus rendering it less susceptible to electrophilic attack. There are found to be buildups of positive potential above the C-NO bonds, indicating that these can serve as initial sites for nucleophilic attack.