MINDO/2 calculations

MINDO/3 calculations, 7, 500 Benzene oxide dipole moment, 7, 553 Benzenes substituted... 

The energies in the upper part of Table 2 are based on an ab initio calculated geometry (STO-3G), whereas those in the lower part are based on a MINDO/3 calculation. 

Table 11. Reaction enthalpies AH" (kJ mol 1) of reactions (11) and (12) from MINDO/3 calculations...

However, in general the MINDO/3 calculations reproduce the experimental heats of formation to satisfaction, as can be seen in Fig. 6. 

Table 14 contains the reaction enthalpies relative to the methyl cation from MINDO/3 calculations. The gas phase values demonstrate the following graduation of stability of the carbocations ... 

Proton affinities of ethene (684 121) and 680129) kJ mol-1) measured experimentally correspond with results from ab initio calculations (698 kJ mol-1 130)). MINDO/3 calculations (with AHf(H+) = 1528 kJ mol-1 91)) also deliver a result of comparable value (714 kJ mol 1) when the formation of a classical carbocation during the protonation is assumed. 

The calculation of an activation barrier for the reactions (21) and (22) must not necessarily be considered as an error of the method. For example, the MINDO/3 calculated activation barrier for the attack of a methyl radical on ethene 137-138) which is comparable to the former reactions was confirmed by experiments 139). In contrast to a free proton (Eq. (20)) the methyl radical as well as the ethyl cation possess steric space need. For this reason, the calculation of repulsive interactions which are able to overcome the attractive forces at certain distances cannot be seen without doubt as faulty. 

The first ionization potentials of several silenes have been predicted using MINDO/3 calculations (177). The ionization potentials found for the parent silene, 8.95 0.1 eV, (174) and 1,1-dimethylsilene, 7.7 eV (184), 7.5 0.3 eV (191), and 8.14 eV (176), have also been estimated from ab initio (174,176) or thermochemical (184,191) calculations. 

As already stated in Section II-B-1, the a-SCSs of substituents X are determined mainly by the electronegativity (X) that is, they are governed by inductive effects (Fig. 1). This has also been verified by ab initio (54), INDO (52), CNDO/2 (95), and MINDO/3 calculations (96). 

Reaction between 79 and formamidine (Scheme 25) gave not 5-methyl-adenine (105), but a rearranged product (106). MINDO/3 calculations show that the two rings in 105 deviate considerably from coplanarity, with loss of conjugation and introduction of strain. Computed bond distances and... 

MINDO/3 calculations of cyclobutane formation reveal a large singlet-triplet splitting of 10 kcal - mol-1 in the cisoid butyl 1,4-diradical, which might be due to a radical-radical interaction.79 The results of a more recent SINDOl calculation are also in agreement with a nonconcerted cleavage of cyclobutane via a diradical pathway.80 Additional quantitative evidence for the 1,4-diradicals has been obtained by thermochemical studies.81... 

Figure 2 Molecular geometry for pyrrole as estimated by MINDO/3 calculations...

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