TY  - JOUR
A1  - Christl, Manfred
A1  - Lang, Reinhard
A1  - Herzog, Clemens
A1  - Stangl, Roland
A1  - Peters, Karl
A1  - Peters, Eva-Maria
A1  - Schnering, Hans Georg von
T1  - Reaktion von Homobenzvalen mit Tetracyanethylen : Bildung eines Tetracyandihydrobarbaralan- und eines Tetracyancyclopropan-Derivats
N2  - In den Reaktionen von Tetracyanethylen (TCNE) und 5,6-Dichlor-2,3-dicyan-p-benzochinon mit Benzvalen haben wir kürzlich die ersten Beispiele für die lange gesuchte einstufige 1,4-Cycloaddition eines Alkens an ein Vinylcyclopropan gcfunden(I~J. Sie ist als [(.,2.+.2s)+ 112J-Prozeß der Dicls-Alder-Addition nahe verwandtllbl. Allerdings entsteht das betreffende TCNE-Addukt, ein Dihydrosemibullvalen-Derivat, nur in einer Ausbeute von wenigen Prozent. Die Hauptprodukte gehen aus einer Zwitterionischen Zwischenstufe hervor, die durch Anlagerung von TCNE an die Benzvalen-n-Bindung resultiert. 

Professor Rolf Huisgen zum 65. Geburtstag gewidmet
KW  - Chemie
KW  - Homobenzvalene
Y1  - 1985
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31839
ER  - 
TY  - JOUR
A1  - Gleiter, Rolf
A1  - Bischof, Peter
A1  - Gubernator, Klaus
A1  - Christl, Manfred
A1  - Schwager, Luis
A1  - Vogel, Pierre
T1  - 2,3-Bis(methylene)bicyclo[2.1.1]hexane and 3,4-Bis(methylene)tricyclo[3.1.0.0\(^{2,6}\)]hexane : Interaction between a π System and a Cyclobutane or Bicyclobutane Moiety
N2  - The He (I) photoelectron spectra of 2-bicyclo[2.1.l]hexene (1), 2,3-bis(methylene)bicyclo[2.1.l]hexane (3), and 3,4-bis(methylene)tricyclo[3.l.O.0\(^{2.6}\)]hexane (4) have been investigated. The assignment given is based on a ZDO model and semiempirical calculations. Tagether with the PE data of benzvalene (2), the reported data allow a comparison between 1-2 and 3-4. This yields a measure of the interactions between 8 cyclobutane or 8 bicyclobutane moiety and a double bond system within a ZDO model. The resonance integral found in the case of 1 and 3 amounts to -1.9 eV, that for 2 and 4, to -2.3 eV. The investigations furthermore reveal that the electronic factors which contribute to the higher reactivity of the bicyclobutane compounds amount to 5 kcal/mol.
KW  - Chemie
Y1  - 1985
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31845
ER  - 
TY  - JOUR
A1  - Metropoulos, B.
A1  - Engels, Bernd
A1  - Peyerimhoff, S.D.
T1  - On the chemi-ionization reaction O + CH ----> HCO\(^+\)+  e\(^-\). Coollinear O-CH Approach
N2  - We have investigated theoretically the importance of the O(\(^3\)P)+CH(a\(^4\sum^-\)) and the O(\(^3\)P)+CH(X\(^2\Pi\)) channels in the collinear chemi-ionization reaction O+CH->HCO\(^+\) +e\(^-\). We have found that both channels may lead to chemi-ionization via favorable Franck-Condon overlaps with the states ofthe ionic species.
KW  - Organische Chemie
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58963
ER  - 
TY  - JOUR
A1  - Engels, Bernd
T1  - Study of influences of various excitation classes on ab initio calculated isotropic hyperfine coupling constants
N2  - Reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. Strang dependence on the method employed for its ca1culation has been found. Within a CI ansatz A\(_{iso}\) is considerably affected by the excitation classes taken into account within the CI calculation. In the present work the influence of various excitation classes on A\(_{iso}\) is examined. Calculations including all single, double, triple and a large part of the quadruple excitations are performed and the individual effects of the excitation classes are studied. It is found that the surprisingly good agreement found for S-CI treatments is due to large error cancellations. The importance of higher than double excitations arises from their indirect influence on the single excitations.
KW  - Organische Chemie
KW  - Spin density
KW  - Hyperfine coupling constants
KW  - Influence of excitation classes
KW  - Indirect and direct contributions to A<sub>iso</sub>
Y1  - 1993
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58973
ER  - 
TY  - JOUR
A1  - Wissing, Elmo
A1  - Kaupp, Martin
A1  - Boersma, Jaap
A1  - Spek, Anthony L.
A1  - Koten, Gerard van
T1  - Alkylation Reactions of Dialkylzinc Compounds with 1,4- Diaza- 1,3-butadienes: Cationic and radical Anionic Organozinc Intermediates. Molecular Structure of the Cationic Organozinc Species [MeZn(t-BuN=CHCH=N-t-Bu)]O\(_3\)SCF\(_3\) and Me\(_2\)Zn(bpy)(bpy = 2,2' -Bipyridine)
N2  - No abstract available
KW  - Anorganische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60008
ER  - 
TY  - JOUR
A1  - Schreck, Michael
A1  - Christl, Manfred
T1  - Freisetzung und Abfangreaktionen von 1-Oxa-3,4-cyclohexadien
N2  - No abstract available
KW  - Chemie
Y1  - 1987
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31597
ER  - 
TY  - JOUR
A1  - Suter, H. U.
A1  - Pleß, V.
A1  - Ernzerhof, M.
A1  - Engels, Bernd
T1  - Difficulties in the Calculation of Electron Spin Resonance Parameters using Density Functional Methods
N2  - Density functional theory is applied to the calculation ofthe isotropic byperfine coupJing constants in some small molecules. Various functionals are tested. The agreement of the calculated values to experimental data and values obtained from sophisticated ab initio methods depends on the functionals used and the system under consideration. With respect to spin density calculations the functional of Lee, Yang and Parr with Becke's excbange functional (BLYP) is found to give good results for tbe heavier center of the CH and the NH molecule, while the spin densities of other molecules such as OH, H\(_2\)CN, H\(_2\)CO\(^+\), NO and O\(_2\) deviate considerably from experimental and/or other theoretical results (30%-60%). In cases where the singly occupied orbital can contribute to the isotropic hyperfine coupling constants, accurate results are obtained. The reason fortbis is analyzed.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59113
ER  - 
TY  - JOUR
A1  - Freund, S.
A1  - Henneberger, H.
A1  - Christl, Manfred
T1  - Halbkäfigverbindungen aus Diels-Alder-Addukten des Benzvalens mit Cyclopentadien-Derivaten durch Radikalreaktionen mit Thiophenol und Bromtrichlormethan
T1  - Half-Cage Compounds by Radical Reactions with Thiophenol and Bromotrichloromethane from Diels-Alder Adducts of Benzvalene with Cyclopentadiene Derivatives
N2  - In Diels-Alder-Reaktionen wurden aus Benzvalen (1) und Tetrachlorcyclopentadienon- dimethylacetal sowie Tetrachlorfuran die Addukte 2 bzw. 8 und 9 erhalten. Behandlung von 2 mit Natrium und tert-Butylalkohol ergab das chlorfreie Acetal 3, dessen Doppelbindung sich mit Diimin unter Bildung von 4 absättigen ließ. Aus dem bekannten Stammkohlenwasserstoff 5 ging analog 6 hervor, und durch Reaktion seines Anions mit Chlorameisensäure- methylester entstand der Ester 7. - Die Verbindungen l, 3, 5, 7-9 und das bekannte U wurden mit Thiophenol so behandelt, daß Radikalkettenreaktionen abliefen. Bei 8 trat Addition an die Zentralbindung des Bicyclobutan-Systems ein. Dagegen unterlag bei 2, 9, U und zum Teil bei 3, deren Doppelbindung jeweils der BicycJobutan-Einheit benachbart ist, das Primärradikal der 5-Hexen-1-yl- Cyclopentylrneth.yl-Umlagerung, aus der letztlich 15, ll, 13 bzw. 16 resultierten. Zum Teil bei 3 und vollständig bei 5 erfolgte die Addition an die Doppelbindung zu 17 bzw. 18, d.h. ohne Beteiligung der benachbarten Bicyclobutan- Einheit. Durch Aktivierung des Bicyclobutan-Systems mit einer Esterfunktion konnte dessen Passivität aufgehoben werden. So entstanden aus 7 das nichtumgelagerte Produkt 19 und das umgelagerte 20. Ihr Verhältnis hing von der Konzentration an Thiophenol ab. - Analog zur Reaktion 1Z + Thiophenol-13 brachte BromtrichJormethan aus 12 das umlagerte Addukt 21 hervor. - Als Nebenprodukt wurde bei der Umsetzung von 12 mit Thiophenol das Chlorwasserstoff-Addukt 14 des ersteren gefunden. Modellreaktionen für die Bildung von 14 sind die Umsetzungen von 12 mit Essigsäure und von 3 sowie 5 mit +Nitrobenzoesäure zu den Addukten 22, 23 bzw. 24. Seit
N2  - The adducts 2, 8,. and 9 were obtained by Diels-Aider reactions of benzvalene (I) with tetrachlorocyclopentadienone dimethyl acetal and tetracblorofuran. respectively. On treatment of 2 with sodium and tert-butyl alcohol, the chlorine atoms were substituted by hydrogen atoms to give acetal 3, the double bond of · whicb could be hydrogenated by diimine with formation of 4. Analogously, the known parent hydrocarbon 5 afforded 6. Tbe anion of 5 reacted with methyl chloroformate to give the ester 7. - Compounds 2, 3, 5, 7-9, and the known 12 were treated with thiophenol under conditions causing radical chain reactions. Whereas 8 added the reagent across the centrat bond of the bicyclobutane system, the additions to 2, 9, 12 and in part to 3, the double bond of which is adjaceot to the bicyclobutane moiety in each case, were accompanied by a 5-hexen-1-yJcylcopentylmethyl rearrangement of the primary radical resulting in formation of 15, 11, 13, and 16, respectively. In part with 3 and completely with 5, the addition took place at the double bond to give 17 and 18, respectively, i.e. without involvement of the adjacent bicylcobutane moiety. Activation of the bicyclobutane system with an ester functionality led to its participation. Thus, compound 7 gave the nonrearranged product 19 and the rearranged one 20 with their ratio being dependent on the concentration of thiophenol. - In analogy to the reaction 12 + thiophenol-13, tbe rearranged adduct 21 was formed from 12 and bromotrichloromethane. - The hydrogen cbloride adduct 14 was found as a byproduct on treatment of 1l witb thiophenol. Model reactions for the formation of 14 are the additions of acetic acid to 12 an~ 4-nitrobenzoic acid to 3 and 5 leading to the adducts 22, 23, and 24, respectively.
KW  - Organische Chemie
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58435
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Henneberger, H.
A1  - Freund, S.
T1  - Halbkäfigverbindungen aus Polycyclen mit einem Bicyclo[1.1.0]butan-System und dazu benachbarter Azobrücke durch Radikalreaktionen mit Thiophenol und Bromtrichlormethan
T1  - Half-Cage Compounds by Radical Reactions with Thiophenol and Bromotrchloromethane from Polycyclic Compounds with a Bicyclo[1.1.0]butane System and an Adjacent Azo Bridge
N2  - Aus Benzvalen (J) und 3,6-Bis(2-pyridyl)-l,2,4,5-tetrazin wurde das Dihydropyridazin 2c erhalten, das ebenso wie die bekannten Dihydropyridazine 2a, b mit Cyclopropen in die entsprechende Azoverbindung 3 überging. Addition von Thiophenol an 3a, c und 5 lieferte unter Beteiligung des Bicyclobutan-Systems und der Azofunktion die Halbkäfigverbindungen 4a, c bzw. 6. Aus der Umsetzung von 7, in dem die Azobrücke durch zwei BicycJobutan- Systeme flankiert ist, mit Thiophenol sowie Bromtrichlormethan gingen die Halbkäfigverbindungen 8 bzw. 9 hervor. An diesen ~eaktionen wirken beide Bicyclobutan-Systeme und die Azofunktion mit.
N2  - Dihydropyridazine 2c was obtained from benzvalene (1) and 3,6- bis(2-pyridyJ)-1,2,4,5-tetrazine. Like the known dihydropyridazines 2a, b. compound 2c was converted into the corresponding azo compound 3 by treatment with cyclopropene. The addition of thiophenol to 3a, c and S yielded the half-cage compounds 4a, c and 6, respectively. In these processes the bicyclobutane system and the azo functionality are involved. Treatment of 7, in which the azo bridge has two bicyclobutane neighbours, with thiophenol and bromotrichloromethane led to the formation of the half-cage compounds 8 and 9, ~spectively. Both the bicyclobuta_ne systems and the azo functionality are transformed in these reactions.
KW  - Organische Chemie
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58440
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Kraft, A.
T1  - Tricyclo[3.1.1.0\(^{2,6}\)]hexandion (das Valen des o-Benzochinons), Bicyclo[2.1.1]hexan-2,3-dion und Valene eines Chinoxalins, des Phenazins sowie eines Benzophenazins
N2  - No abstract available
KW  - Organische Chemie
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58459
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Kraft, A.
T1  - Tricyclo[3.1.1.0\(^{2,6}\)]hexandion (the Valen of o-Benzochinons), Bicyclo[2.1.1]hexan-2,3-dion and Valene of a Chinoxalins, of Phenazins and of a Benzophenazine
N2  - No abstract available
KW  - Organische Chemie
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58462
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Brunn, E.
A1  - Roth, W. R.
A1  - Lennartz, H.-W.
T1  - 7-Methyl- and 7-Phenylcyclohepta-1,3,5-trienes from Benzvalene Via 3,3a,4,5,6,6a-Hexahydro-4,5,6-methenocyclopentapyrazoles and Tetracyclo[4.1.0.0\(^{2,4}\).0\(^{3,5}\)]heptanes
N2  - No abstract available
KW  - Organische Chemie
Y1  - 1989
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58471
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Brunn, E.
A1  - Kraft, A.
A1  - Irngartinger, H.
A1  - Huber-Patz, U.
T1  - Nichtbindende Wechselwirkungen in zwei 7-Spirotetracyclo[4.1.0.0\(^{2,4}\).0\(^{3,5}\)]heptanen
T1  - Nonbonded Interactions in two 7-Spirotetracyclo[4.1.0.0\(^{2,4}\).0\(^{3,5}\)]beptanes
N2  - Die Reaktion von Tetrachlordiazocyclopentadien mit Be.nzvalen (2) ergab das Fulven-Derivat 3. Dagegen führten die Umsetzungen von Diazoßuoren und 5-Diazo-10,1 1-dihydro-SH-dibenzo[ a.d]cyclohepten mit 2 zu den erwarteten Spiro-1-pyrazolinen 4 bzw. 5. Die photolytische Abspaltung von Stickstoff aus 4 und 5 lieferte die Spirotetracycloheptane 6 bzw. 7. Die Röntgenstrukturanalyse von 6 beweist einen engen Kontakt zwischen je eineßl Wasserstoffatom der Tetracycloheptan- und der Fluoren-Einheit. Dieser kurze Abstand (2.15 A) ruft Winkelaufweitungen hervor und wird auch als Grund für starke Entschirmungen der betreffenden Protonen und eine formal über sieben Bindungen reichende 0.6-Hz-Kopplung zwischen ihnen angesehen. 7 ist das erste chiralc Tetracyclohcptan. Ursache dafür ist eine nichtebene Konformation des Siebenrings, der bei Raumtemperatur nicht invertiert. Auf der Basis von NOE-Messungen gelang die Zuordnung der tH-NMR-Signale von 6 und 7.
N2  - The reaction or tctrachlorodiazocyclopentadiene with benzvalene (2) gavc, the fulvene derivative 3. In contrast, treatment of diazoßuorene and 5-diazo-1 0,1 1-dihydro·SH -dibenzo[ a,d]cycloheptene with l:afl'orded the expected spiro-1-pyrazolines 4 and 5, respectively. Photolytic extrusion of nitrogen from 4 and S led to the corresponding spirotetracyclobeptanes 6 and 7. The X-ray structure analysis of 6 revealed a close contact between one hydrogen atom cach of the tetracycloheptane and the ßuorene subunits. This short distance (2.15 A) causes an increase in bond angles and is believed to produce strong deshielding of the respective protons and a 0.6-Hz coupling between them, which is formally a long-range coupling across seven bonds. Compound 7 is the first chirat tetracycloheptane. This is due to a nonplanar confonnation of the seven-membered ring, which does not invert at room temperature. On tbe basis of NOE measurements the 1H-NMR signals of 6 and 7 are assigned.
KW  - Organische Chemie
KW  - 5H-Dibenzo[a
KW  - d]cycloheptene
KW  - 10
KW  - 11-dihydro- / 1-Pyrazoline
KW  - Nonbonded Interactions
KW  - Spirotetracyclo[4.1.0.0<sup>2
KW  - 4</sup>.0<sup>3
KW  - 5</sup>]beptanes
KW  - Long-range coupling constants
KW  - mtrogen extruston
Y1  - 1989
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58489
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Braun, Max
T1  - Photocycloadditionen des Benzvalens
N2  - No abstract available
KW  - Organische Chemie
Y1  - 1989
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58492
ER  - 
TY  - JOUR
A1  - Christl, Manfred
A1  - Braun, Max
T1  - Photocycloadditions of Benzvalene
N2  - No abstract available
KW  - Organische Chemie
Y1  - 1989
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-58506
ER  - 
TY  - JOUR
A1  - Mühlhäuser, M.
A1  - Froudakis, G.
A1  - Zdetsis, A.
A1  - Engels, Bernd
A1  - Flytzanis, N.
A1  - Peyerimhoff, S. D.
T1  - Ab initio investigation of the stability of Si\(_3\)C<\(_3\) clusters and their structural and bonding features
N2  - Various structural possibilities for Si\(_3\)C\(_3\) clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si - C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59060
ER  - 
TY  - JOUR
A1  - Wortmann-Saleh, D.
A1  - Engels, Bernd
A1  - Peyerimhoff, S. D.
T1  - Theoretical Study of the Reaction O(\(^3\)P) + C\(_2\)H\(_4\) and comparison with the \(^3\)CH\(_3\) + C\(_2\)H\(_4\) Reaction
N2  - The minimum energy path for the reaction O(\(^3\)P\(_g\)) + C\(_2\)H\(_4\)(\(^1\)A\(_g\)) has been calculated by optimizing all relevant geometrical parameters along the approach of oxygen to ethene. A barrier of 4.7 kcal/mol in the \(^3\)A"( ... 9a'\(^2\)- 10a'3a") potential energy surface and an energy difference of 14.4 kcal/mol between the product and the fragments is found at the multireference-configuration interaction level. The corresponding values at the lower-level treatment CASSCF are 9 kcal/mol for the barrier and 9 kcal/mol for the depth of the potential; this shows the importance of inclusion of electron correlation. The barrier for CH\(_2\) rotation for the lowestenergy structure (asymmetric OC\(_2\)H\(_4\)) is around 5 kcal/mol. The energy gap to the first excited state \(^3\)A'( ... 9a'l0a'3a'12) is found tobe 3.6 kcal/mol in MRD-CI calculations at the ground-state minimum. Comparison with \(^3\)CH\(_2\) + C\(_2\)H\(_4\) shows that in this system the lowest-energy surface is \(^3\)A', i.e., the state which is the excited state in 0 + C\(_2\)H\(_4\). This difference in energy ordering of \(^3\)A' and \(^3\)A" states results from the fact that the p\(_x\), p\(_y\), p\(_z\) degeneracy of oxygen orbitals is lifted in \(^3\)CH\(_2\)leading to b\(_1\), b\(_2\). and a\(_1\) MOs whereby the lowest b\(_2\) (a") remains doubly occupied; as a consequence, the reaction pattem between the oxygen and \(^3\)CH\(_2\) approach is different, which is also quite apparent in the calculated charge transfer.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59076
ER  - 
TY  - JOUR
A1  - Staikova, M.
A1  - Peric, M.
A1  - Engels, Bernd
A1  - Peyerimhoff, S. D.
T1  - Ab initio Investigation of the Structure of the X\(^2\)A', A\(^2\)A'' (1\(^2\)Π) Spectral System of HCO: Investigation of the Magnetic Hyperfine Effects
N2  - Results ofan ab initio study ofthe hyperfine structure of the X\(^2\)A', A\(^2\) A" ( 1\(^2 \Pi\)) system ofthe formyl radical are presented. Special attention is paid to the analysis of the interplay between the vibronic and magnetic hyperfine etfects. The results of computations are in very good agreement with the available experimental findings. The values for the hyperfine coupling constants in lower bending Ievels of both electronic species are predicted.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59089
ER  - 
TY  - JOUR
A1  - Froudakis, G.
A1  - Zdetsis, A.
A1  - Mühlhäuser, M.
A1  - Engels, Bernd
A1  - Peyerimhoff, S. D.
T1  - A comparative ab initio study of the Si\(_2\)C\(_4\), Si\(_3\)C\(_3\), Si\(_4\)C\(_2\) clusters
N2  - Various structural possibilities for the Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si\(_3\)C\(_3\) clusters is found to be fully operative for Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters. A comparison of the structure and stability of various geometrical arrangements in the series C\(_6\) , Si\(_2\)C\(_4\) , Si\(_3\)C\(_3\) , Si\(_4\)C\(_2\), and Si\(_6\) shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si\(_6\) structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59097
ER  - 
TY  - JOUR
A1  - Suter, H. U.
A1  - Huang, M.-B.
A1  - Engels, Bernd
T1  - A Multireference Configuration Interaction Study of the Hyperfine Structure of the Molecules CCO, CNN and NCN in their triplet ground states
N2  - The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X\(^3 \sum ^-\)) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B\(_K\)) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
KW  - Organische Chemie
Y1  - 1994
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-59108
ER  -