3-21G basis set

FuUerene compounds have receieved a lot of attention in recent years. In this exercise we predict the energy of Cgg and look at its highest occupied molecular orbital, predicted at the Hartree-Fock level with the 3-21G basi set. Include SCF=1ight in the route section of the job. 

Q the STO-3G or 3-21G basis set. Include SCF=NoVbrAcc in the route section of your job... 

Clearly, the 3-21G basis set reproduces the experimental results much better than STO-3G. We ll look at basis set effects in detail in Chapter 5. ... 

Nitrones are a rather polarized 1,3-dipoles so that the transition structure of their cydoaddition reactions to alkenes activated by an electron-withdrawing substituent would involve some asynchronous nature with respect to the newly forming bonds, especially so in the Lewis acid-catalyzed reactions. Therefore, the transition structures for the catalyzed nitrone cydoaddition reactions were estimated on the basis of ab-initio calculations using the 3-21G basis set. A model reaction indudes the interaction between CH2=NH(0) and acrolein in the presence or absence of BH3 as an acid catalyst (Scheme 7.30). Both the catalyzed and uncatalyzed reactions have only one transition state in each case, indicating that the reactions are both concerted. However, the synchronous nature between the newly forming 01-C5 and C3-C4 bonds in the transition structure TS-J of the catalyzed reaction is rather different from that in the uncatalyzed reaction TS-K. For example, the bond lengths and bond orders in the uncatalyzed reaction are 1.93 A and 0.37 for the 01-C5 bond and 2.47 A and 0.19 for the C3-C4 bond, while those in... 

Fig. 8.5 The calculated transition-state structure for the reaction of acrolein with butadiene leading to carbo-Diels-Alder adduct catalyzed by BH3 using a RHF/3-21G basis set [6]...

Fig. 3-2. Molecular electrostatic potential with 6-31G //3-21G basis set in the molecular plane of (ii)-nitrous acid. Black dots refer to four different protonation sites in potential minima. For values of isopotential contours see Nguyen and Hegarty, 1984.

Interestingly, preliminary calculations (3-21G basis set) estimate the AH of the triplet SO (and ethylene) generation from the parent thiirane oxide (16a) to be about 18kcalmol-1 166. 

Recently, Wolfe and coworkers50,51 recalculated the same molecule using a new 3-21G basis set which includes the participation of 3d orbitals and revealed that the most... 

Table 11 summarizes the relative conformation stabilities of various sulfmyl carbanions, based on the H/D exchange rates of the corresponding sulfmyl compounds 36-39. The results are in good agreement with the order of stabilities obtained from the MO calculations using the 3-21G basis set. This is remarkable, since the calculation did not take into consideration the solvent effect, despite the strong unsymmetrical solvation on the a-sulfmyl carbanion. 

Table II. Differences in Mulliken population analyses for an Si50i5Hi2 molecule and four combinations of point-ion cluster, using a 3-21G basis set...

The interaction between H+, Li+, and Na+ cations and nitrosourea, as well as methyl, ethyl, and chloroethyl di azohydroxides (E and Z isomers) has been investigated with ab initio calculations, using the STO-6G and the 3-21G basis sets.13 The resulting affinities show... 

The complex formed by thymine with the guanidinium ion (Figs. 6.7, 6.8) and the complex formed by thymine with the aminopyrolidinium ion (Figs. 6.9,6.10) were subjected to ab initio (Hartree-Fock) calculations using the 6-31G find the 3-21G basis sets, in order to... 

A quantum mechanical ab initio calculation using a 3-21G basis set without further geometry optimization (single point calculation) was subsequently performed on all AMI optimized (minimized) conformations using the Spartan program. 

The dipole moments of both 3- and 4-phenylsydnones containing dimethylamino and nitro substituents were calculated (ah initio 3-21G basis set) the magnitude increases with the electron donor attached to the phenyl ring <1995JPC1923>. Quadrupole moments, octopole moments, and polarizability of 1,2,3-oxadiazole have been determined by ab initio calculations and simple models <1996JPC8752, 1999JPC10009>. 

FIGURE 33. Energy difference A between MOs. T and 7T- of two ethylene molecules as a function of their distance R as calculated by an ab initio method (using the 3-21G basis set), by AMI and by INDO/S. Note the strong underestimation of the through-space interaction by AMI at all distances and the overestimation by INDO/S which diminishes, however, for large R... 

The through-bond conjugation with strong ct-tt mixing for tetrasila-cycloocta-l,5-diyne is further demonstrated by photoelectron spectroscopic (15) and ab initio (3-21G basis set) studies (16). 

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