Single-crystal X-ray diffraction analysis is the most direct and definitive technique for determining (or confirming) the geometric structure of chemical compound. In this paper, we describe the capacity of semi-empirical methods such as AM1, PM3, PM6 and NODCs for determining interatomic distances and bond angles for three compounds
P1 ((1S, 3R,8R)-2,2-dichloro-3,7,7,10-tetramethyl-tricyclo [6,4,0,01,3] dodec-9-ene), P2 (1S,3R,8R,9S,11R)-2,2,10,10-tetrachloro-3,7,7,11 tetramethyltetracyclo [6,5,0,01.2,09.116 ] tridecane) and P3 (1S,3R,8R,9S,11R)-2,2,10,10-tetrabromo-3,7,7,11 tetramethyltetracyclo [6,5,0,01.2,09.116 ] tridecane) including experimental data interatomic distances and bond angles are available. The results obtained show a good agreement with experimental reference values, a few exceptions, for semi-empirical methods AM1 and PM6 appear more reliable than PM3 and NODC.
In this work we used density functional theory (DFT) B3LYP/6-31G*(d) to study the stoichiometric reaction between the β-himachalene and dibromocarbene. We have shown that β-himachalene behaves as a nucleophile, while dibromocarbene behaves as an electrophile; that the chemical potential of dibromocarbene is superior to that of β-himachalene in absolute terms; and that β-himachalene reacts with an equivalent quantity of dibromocarbene to produce only one products P1: (1S,3R,8S) -2,2- dibromo -3,7,7,10
In this work, we determined the tensors of screen as well as the chemicals shifts of the nuclear magnetic resonance of the carbon 13 (RMN 13C) of organic product: P1 :[(1S, 3R, 8R)-2,2- dichloro -3, 7, 7, 10-tetra- methyl-tricyclo [6, 4, 0, 01,3] dodec-9-ene], using methods: CSGT (Continuous Set of Gauge Transformations), IGAIM (a slight variation on the CSGT method) and GIAO (Gauge-Independent Atomic Orbital), using the method DFT by means of functional B3LYP / 6-311 (2d, p) for the geometrical optimization of this product. These methods are implanted in the software Gaussian09. The comparison of the theoretical results to the experimental results shows that the method GIAO is the most reliable. On the other hand we calculate the chemicals shifts of the carbon 13 (13C of the compound P2 :[(1S, 3R, 8R) -2, 2- dichloro-3, 7, 7, 10 -tetramethyl- tricycle [6, 4, 0, 01,3 ] dodec-9-
The reaction between α-trans-himachalene and dichlorocarbene has been studied using density functional theory (DFT) B3LYP/6-311G (d, p). The global electrophilicity and global nucleophilicity indices indicate that α-trans-himachalene behaves as a nucleophile while dichlorocarbene behaves as an electrophile. The majority product obtained by stoichiometric reaction between dichlorocarbene and α-trans-himachalene is (1R, 2S, 4R, 7S)-3,3-dichloro-8-methylene-4,12,12-trimethyl-tricyclo [5.5.0.02,4] dodecane (referred to here as P1(α)): in this reaction the attack takes place at the endocyclic double bond at the α side of α-trans-himachalene. The majority product obtained by the reaction between two equivalents of dichlorocarbene with α-trans-himachalene is (1R, 2S, 4R, 7S, 8R)-3,3,13,13-tetrachloro-4,12,12-trimethyl-tricyclo [5.5.0.02,4] -spiro[28] tetradecane (referred to here as P2(β)): here the attack takes place at the β side of the exocyclic double bond. P2(β) is also obtained by the equimolar reaction of P1(α) with dichlorocarbene. P1(α) and P2(β) are both exothermic. Analysis of local electrophilicity and local nucleophilicity indices demonstrates the chemo-, regio- and stereoselectivity of the reaction. Analysis of the potential energy surface shows that this reaction follows an asynchronous concerted mechanism. Calculating the intrinsic reaction coordinate (IRC) shows that the reaction mechanism can be characterized as "one-step" and "two-stage". Stationary points were characterized by frequency calculations in order to verify that the transition states had one and only one imaginary frequency.
β-himachalene behaves as a nucleophile while dichlorocarbene behaves as an electrophile. Equimolar condensation of β-himachalene and dichlorocarbene results in a single product: (1S,3R,8R)-2,2-dichloro-3,7,7,10-tetramethyltricyclo[6,4,0,01.3]dodec-9-ene, also referred to as dichlorocarbene β-himachalene ? (referred to as P1 here), formed by reaction at the ? side of the C6=C7 double bond of β-himachalene. This regioselectivity is controlled by the frontier orbitals, as is the reaction mechanism. Electron density is particularly high around the C6=C7 double bond of the HOMO orbital. However when β-himachalene reacts with two equivalents of dichlorocarbene under the same conditions the result is two products: (1S,3R,8R,9S,11R)-2,2,10,10-tetrachloro-3,7,7,11-tetramethyltetracyclo[6,5,0,01.2,09.11]tridecane and (1S,3R,8R,9R,11S)-3,7,7,11-tetrachloro-3,7,7,11-tetramethyltetracyclo[6,5,0,01.2,09.11]tridecane (referred to here as P2 and P3 respectively). The same two products are also obtained when P1 reacts with one equivalent of dichlorocarbene. The attack takes place simultaneously at the ? and β sides of the C2=C3 double bond. Study of the two reactions using the ab-initio quantum density functional theory method (B3LYP/6-31G(d)) shows that they are stereoselective, chemospecific, concerted and exothermic. P3 is formed in greater quantity than P2.
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