Natural population analyses

Natural bond order analysis (NBO) is the name of a whole set of analysis techniques. One of these is the natural population analysis (NPA) for obtaining... 

Natural population analysis is carried out in terms of localized electron-pair bonding units. Here are the charges computed by natural population analysis (the essential output is extracted) ... 

Natural population analysis of transition-metal-fluoride wavefunctions gives orbital populations that are generally consistent with the expected configurations, but with large departures from an idealized ionic picture. Table 2.4 compares the... 

Table 3.40 displays the calculated 0b charges from natural population analysis (NPA) for all unique B atoms. This table also includes comparison of the NPA charges with corresponding zeroth-order (ZO) estimates given by Lipscomb, which are based essentially on the formal charges for conjectured three-center bond and. s /vx-code assignments for each species (to be discussed below). 

Details on the numerical evaluation of the descriptors will be given in the individual cases but in most cases a computational DFT approach is used, with a hybrid functional of the B3LYP type [32]. Condensation of f(r) or sir) is done with conventional population analysis techniques (Mulliken [33], Natural Population Analysis (NPA) [34]) or with the Hirshfeld technique [35], often used by our group [36]. 

Figure 1. Natural population analysis (6-311C ) of benzocyclopropenyl cation 273 and its 1-fluoro derivative 282.

Natural population analysis was carried out on 273 and 282. As shown in Figure 1, the positive charge of both cations is localized on the carbon atoms of the three-membered ring. This is consistent with the conclusion, based on C chemical shifts of benzocyclopropenyl cations, that about 45% of the positive charge resides in the cyclopropene moiety. ... 

Several computational studies have addressed whether the dipolar cycloaddition of nitronates is a concerted or stepwise process (93,100). Natural population analysis reveals that their is very little zwitterionic character in the transition state. The formation of the C C bond marginally precedes the C—O bond on the basis of calculated bond lengths and orders in the transition structure. These calculations also show that the reaction is a concerted process that is shghtly asynchronous. In addition, the cycloaddition likely proceeds through an early transition state and is overall an exothermic process. 

NICS NPA nucleus-independent chemical shift natural population analysis... 

Table 7.6 Comparison of Mulliken and natural bond orbital (NBO)/natural population analysis (NPA) charges in LiH and LiF using different basis sets and computational approaches. ...

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