Opening of a cyclopropyl ring in (diphenylcyclopropyl)alkenes promoted by electron transfer from potassium 4,4'-di-tert-butylbiphenyl radical anion and x-ray and theoretical calculations of the structure of (Z)-1,2-bis(trans-2,trans-3-diphenylcyclopropyl)ethene (original) (raw)
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Structural Chemistry, 1997
The crystal structure of 4-cyclopropylacetanilide was investigated at room temperature (21 ~ and at-100~ in order to determine the orientation of the phenyl ring with respect to the cyclopropane moiety and the effect of this substituent on the stereochemistry of the three-membered ring. The compound was chosen because it is one of the few species containing a simple phenyl ring as the sole cyclopropane ring substituent and whose crystals are suitable for X-ray diffraction at room temperature. The substance crystallizes in space group P21/c at either temperature (no phase transitions) with cell constants: (at 21~ a = 9.725(2), b = 10.934(3), and c = 9.636(2) .A., ~ = 106.13(1)~ V = 984.21 ~3 and d(calc; z = 4) = 1.182 g cm-3. The relevant parameters for the-100*C structure are a = 9.557(4), b-I0.980(2), and c = 9.641(2) ,~,/~ = 106.34(3)~ V = 970.76 ,~3 and d(calc; z = 4) = 1.199 gcm-3. Final values were R(F) = 0.042, Rw = 0.035, using unit weights, and its nonhydrogen atoms were used to phase the low-temperature data, whose final discrepancy indices were R(F) = 0.051, Rw = 0.061. The phenyl substituent is almost exactly in the bisecting conformation with respect to the CC -C angle at the point of attachment to cyclopropane and conjugative effects are clearly evident in the lengths of the cyclopropane ring [1.494(3), 1.498(3), and 1.474(4) A, the later being the distal bond]. If one omits the terminal methylene fragments at C 10 and C 11, the atoms comprising the acetanilide fragment and the substituted carbon of the cyclopropane ring lie in a nearly perfect plane. Molecular mechanics as well as semiempirical (AM 1) calculations were carried out in order to determine the structure of the energy-minimized configurations in the two computational environments. The molecular conformations thus obtained are close to that experimentally observed from the X-ray diffraction experiment. In both theoretical models, the lowest energy conformation is that in which the plane of the phenyl ring bisects the cyclopropane CC -C angle as was experimentally observed. Finally, the shape of the conformational barrier as a function of the orientation of the plane of the phenyl ring was computed, giving a maximum barrier to rotation of 2.2 kcal/mol. Similar calculations were carried out for two other aryl cyclopropanes, whose rings (naphthalene and anthracene) cannot adopt the bisecting position. Comparisons of experimental geometrical parameters as well as of the barriers to rotation are presented. KEY WORDS: Cyclopropane structures; phenylcyclopropanes; molecular mechanics and semiempirical computations in phenylcyclopropanes and related molecules.
Journal of The American Chemical Society, 1986
Restricted Hartree-Fock calculations have been carried out for 1,3,&cycloheptatriene, norcaradiene, lH-azepine, benzenimine (azanorcardiene), oxepine and benzene oxide (oxanorcaradiene) employing the STO-3G, 4-31G and 6-31G* basis sets. Theoretical geometries, conformations and barriers to ring inversion have been obtained and compared with the available experimental structural data. It has been found that the cyclotrienes possess a boat conformation with a constant admixture of 22% chair character leading to a flattening of the triene part and n-electron delocalization typical for a planar polyene. The structural data obtained in this work suggest that cyclic delocalization of either 6~ (homoaromaticity) or 8~ electrons (antiaromaticity) is not present in the three cyclotrienes. The former possibility, however, cannot be excluded in the case of the three norcaradienes.
The Journal of Physical Chemistry, 1996
The aromatic stabilization energy of the cyclopropenyl cation (CH) 3 + is assessed with G2 theory by calculating its homodesmotic stabilization energy (247.3 kJ mol-1) and by comparing the ionization energies of the cyclopropenyl radical (6.06 eV) and the cyclopropyl radical (8.24 eV). These data indicate substantial stabilization of the two π-electron system in what is considered the archetypal aromatic cation. The calculated enthalpy of formation of the cyclopropenyl cation is 1074.0 kJ mol-1 and agrees with the experimental estimate of 1075 kJ mol-1. The small stabilization energy of the cyclopropenyl radical (37.4 kJ mol-1) suggests that this radical should not be classified as aromatic, in contrast to earlier suggestions. Our G2-calculated enthalpy of formation of the cyclopropenyl radical (∆H f 298) 487.4 kJ mol-1) and its ionization energy are different from experimental estimates and suggest that the experimental values may need to be revised. The most stable structure for the cyclopropenyl anion is a nonplanar C s singlet structure containing a strongly pyramidalized carbon. The open-chain isomers of (CH) 3as well as the nonplanar triplet cyclic structures are all found to be higher in energy. The nonplanar C 2 "allylic-type" cyclic structure of (CH) 3is 8.9 kJ mol-1 higher energy than the cyclic C s structure and corresponds to a first-order saddle point. While the G2 stabilization energy of the cyclopropenyl anion estimated using the energy of the homodesmotic reaction cyclopropenyl anion + cyclopropane f cyclopropene + cyclopropyl anion is negative (-17.3 kJ mol-1), its absolute value is substantially less than the corresponding stabilization energy calculated for cyclobutadiene (-129.6 kJ mol-1). A comparison of the G2-calculated gas-phase acidities of cyclopropene (1755.4 kJ mol-1) and cyclopropane (1737.1 kJ mol-1) also suggests the antiaromatic destabilization energy of the cyclopropenyl anion to be small. However, the electron affinity of the cyclopropenyl radical is found to be negative (-0.18 eV), indicating that the cyclopropenyl anion is not bound in the gas phase.
Journal of The American Chemical Society, 1985
Restricted Hartree-Fock calculations have been carried out for 1,3,&cycloheptatriene, norcaradiene, lH-azepine, benzenimine (azanorcardiene), oxepine and benzene oxide (oxanorcaradiene) employing the STO-3G, 4-31G and 6-31G* basis sets. Theoretical geometries, conformations and barriers to ring inversion have been obtained and compared with the available experimental structural data. It has been found that the cyclotrienes possess a boat conformation with a constant admixture of 22% chair character leading to a flattening of the triene part and n-electron delocalization typical for a planar polyene. The structural data obtained in this work suggest that cyclic delocalization of either 6~ (homoaromaticity) or 8~ electrons (antiaromaticity) is not present in the three cyclotrienes. The former possibility, however, cannot be excluded in the case of the three norcaradienes.
Theoretical study of the cyclopropenyl radical
Journal of the American Chemical Society, 1984
Comprehensive ab initio MCSCF and CI calculations are performed to determine properties of the cyclopropenyl radical, which has not yet been directly observed experimentally. Jahn-Teller distortion is responsible for a dramatic change from the high-symmetry D3* a radical parent structure to a low-symmetry nonplanar C, u radical equilibrium structure. The equilibrium structure is found to be an ethylenic form that can exist in three equivalent conformations. These can interconvert (via a pseudorotation of the carbon-carbon double bond around the ring) by passing through a nonplanar allylic transition state. Planar geometries turn out to be of such high energy as to play no significant role in the dynamics of this system. Large-scale CI calculations, with corrections for differences in zero-point vibrational energies, indicate the pseudorotation barrier height to be about 3-4 kcal/mol. Qualitative results are obtained for the energy and geometry changes that occur along the interconversion path. A number of one-electron properties are also reported for the equilibrium form. Notable among these are the spin-density predictions, which should be of use in experimental identification of the cyclopropenyl radical by ESR spectroscopy. A qualitative survey of the energies and geometries of other C3H3 isomers is also presented.
Photochemical & Photobiological Sciences, 2012
Radical ion pairs generated by photo-induced electron transfer from 1,2-disubstituted cyclopropanes to various acceptors undergo return electron transfer in pairs of singlet and triplet multiplicity. The pair energies relative to the reactant ground states and to accessible triplet states, respectively, determine the competition between the recombination pathways. The potential surfaces of the radical cations and triplet states of 1,2-diphenyl-, 1, and 1,2-dimethylcyclopropane, 2, have been examined by density functional theory calculations. The radical cation surfaces have minima at geometries that retain significant bonding between C-1 and C-2, preventing geometric isomerization of the radical cations. The triplet potential surfaces are dissociative with minimal rotational differentiation at long distances between C-1 and C-2. † This article is published as part of a themed issue in honour of Professor Kurt Schaffner on the occasion of his 80th birthday. ‡ Electronic supplementary information (ESI) available. See
Journal of Molecular Structure, 1995
The molecular structure and conformational composition of (silylmethyl)cyclopropane (SMCP), C3Hs-CH2-SiH3, with respect to the Cring-CH 2 and the CH2-Si axes have been studied by gas-phase electron diffraction and ab initio calculations using a 6-31 G* basis set. The conformational analysis, with respect to the Cring-C bond, has shown that the gauche (skew) form is the predominant conformation (> 98%) in the gas phase. A reasonable explanation for the preference of the gauche conformation is provided by the a-Tr hyperconjugation effect. Repulsive through-space interactions are most probably responsible for the cis conformer, being higher in energy and thus less favorable. The major bond distances (ra, A.-I) and angles (°) for the skew conformer obtained from the least-squares refinements with uncertainties estimated at 3~r are r(C H)= 1.120(4), r(Cl-Ce)ring = 1.510(10), r(C2 C3)ring = 1.490(12), r(Cring C) = 1.540(10), r(Si-C)= 1.876(2); ZHSiC = 111.0(2.0), ZSiCC = 112.1(1.0), ZC C(ring plane)= 122.7(0.5), and the dihedral torsional angle %iccx = 119.0(2.0) (X is the center of the ring).
The Journal of Organic Chemistry, 1990
A = 0.71069). Only random fluctuations of less than 2% in the intensities of two standard reflections were observed during the course of data collection. The structure of N-(1-phenylethy1)methanesulfinamide was solved by direct methods and an absorption correction was applied. Final refinement was carried out with anisotropic thermal parameters for all non-hydrogen atoms. The largest feature on a final difference map was 0.31 e A-3 in height. The largest shift in the final cycle of refinement was 0.030 for overall scale. A summary of the relative experimental parameters for the X-ray structure determination of the sulfinamide, atomic coordinates, isotropic thermal parameters, a listing of the bond distances and bond angles as well as hydrogen-atom coordinates are given as supplementary materials. A computer projection of the structure is reproduced in Figure 1. The relative experimental parameters for the X-ray structure determination of 3-((1-phenylethy1)ammonio)propanesulfinate are summarized in the supplementary material. No decay in the intensities of two standard reflections was observed during the course of data collection. The structure was solved by direct methods, and an absorption correction was applied. The handedness was determined to be correct as found by use of the SHELXTL routine for this purpose. Final refinement was carried out with anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms bonded to carbon were included at calculated positions using a riding model, with C-H of 0.96 A and UH = 1.2Uc. The largest feature on a final difference map was 0.65 e A-3 in height in the approximate position of the sulfur lone pair. The largest shift in the final cycle of refinement was 0.013. Atomic coordinates, isotropic thermal parameters, a listing of the bond distances and bond angles as well as hydrogen-atom coordinates are given as supplementary material. A computer projection of the structure is reproduced in Figure 2. Supplementary Material Available: The relative experimental parameters for the X-ray structure determination of the sulfinamide along with atomic coordinates, isotropic thermal parameters, a listing of the bond distances and bond angles as well as hydrogen atom coordinates for N-(1-phenylethy1)methanesulfinamide and 3 4 (1-phenylethy1)ammonio)propanesulfinate (7 pages). Ordering information is given on any current masthead page.
Small-ring cyclic alkynes: ab initio molecular orbital study of cyclohexyne
The Journal of Organic Chemistry, 1987
The structures of the lowest energy singlet and triplet electronic states of cyclohexyne have been determined by ab initio MO theory at the G V B and UHF levels, respectively, with the split-valence 3-21G basis set. Both electronic states prefer a Cz nonplanar structure. Harmonic force constant calculations on the optimized structures demonstrate that both singlet ('A) and triplet (3B) cyclohexyne are relative minima on the corresponding C6H8 potential-energy hypersurface. The triplet state is predicted to lie about 42 kcal/mol above the ground-state singlet. Harmonic vibrational frequencies are predicted for both electronic states. The triple-bond harmonic stretching frequency for singlet cyclohexyne is predicted to be 2003 cm-', whereas the analogous stretching frequency for the triplet state is 1663 cm-'. In terms of C=C bond distance, diradical character, singlet-triplet energy separation, and C=C stretching frequency, cyclohexyne should be considered as a normal, yet strained, alkyne. (1) (aPericls, M. A.; Riera, A.; Solb, A. J. Chem. Res. (s) 1985,328. (b) Olivella, S.; Pericls, M. A,; Riera, A.; Solb, A. J. Am. Chem. SOC. 1986. 108. 6884. (8) Olivella,'S.; Pericls, M. A,; Riera, A.; Solb, A. J. Chem. Soc., Perkin (9) Krebs, A.; Cholcha, W.; Muller, M.; Eicher, T.; Pielartzik, H.;