A theoretical study using ab initio methods of tautomerism in cytosine in the gas phase and in water

1992 ◽  
Vol 57 (16) ◽  
pp. 4434-4437 ◽  
Author(s):  
Ian R. Gould ◽  
Darren V. S. Green ◽  
Philip Young ◽  
Ian H. Hillier
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Ab Initio Methods

A theoretical study, using ab initio methods, of tautomerism in 3-amino-1,2,4-triazole in the gas phase and in aqueous solution

1992 ◽  
pp. 1681 ◽  
Author(s):  
Oswald G. Parchment ◽  
Ian H. Hillier ◽  
Darren V. S. Green ◽  
Neil A. Burton ◽  
John O. Morley ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Ab Initio Methods

On the possible formation of Si=O, Si=S, and Si=Se double bonds via the reaction of silylenes with oxirane, thiirane, and selenirane, respectively. An ab initio theoretical study

2000 ◽  
Vol 78 (11) ◽  
pp. 1496-1510 ◽  
Author(s):  
Yitzhak Apeloig ◽  
Stepan Sklenak
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Single Step ◽  
Membered Ring ◽  
Basis Set ◽  
Double Bonds ◽  
Ring Compounds ◽  
Encounter Complex

The reactions between silylene, H2Si, and the three-membered ring compounds, oxirane (9), thiirane (10), and selenirane (11), which provide possible routes to Si=X (X = O, S, Se) double bonds were studied by ab initio calculations at the MP2 and QCISD correlated levels of theory employing the polarized 6-31G** basis set. The calculations show that the three reactions are all highly exothermic, (–61.8, –45.2, –52.9 kcal/mol at MP2/6-31G**//MP2/6-31G** for X = O, S, Se, respectively). In the gas phase, at 0 K, these reactions are predicted to be also spontaneous (i.e., the calculated transition states are lower in energy than the reactants). At 298 K, entropy contributions result in small barriers on the ΔG surface for X = O, S (7.4 kcal/mol for both reactions at QCISD (full)/6-31G**), but for X = Se the reaction remains spontaneous. Thus, the calculations suggest that these reactions are viable routes for the preparation of compounds with Si=X (X = O, S, Se) double bonds. The first step in all the reactions is the barrier-less formation of an encounter-complex between the silylene and the X atom of the precursor. For X = O, S, these complexes are predicted to be sufficiently stable to be observed in a matrix. The reaction steps which follow depend on X; for X = O fragmentation of the silylene-XC2H4 complex proceeds in two steps via a biradical intermediate, while for X = S and X = Se the fragmentation occurs in a single step. The first ab initio calculations for H2Si=Se are reported.Key words: silylene, silanone, silanethione, silaneselone.

AB-INITIO THEORETICAL APPROACHES TO THE STRUCTURAL, ELECTRONIC AND VIBRATIONAL PROPERTIES OF SMALL CLUSTERS AND FULLERENES: THE STATE OF THE ART

1993 ◽  
Vol 04 (02) ◽  
pp. 227-237
Author(s):  
WANDA ANDREONI
Keyword(s):  
Ab Initio ◽  
Vibrational Spectra ◽  
Theoretical Study ◽  
State Of The Art ◽  
Electronic States ◽  
Vibrational Properties ◽  
Ab Initio Methods ◽  
Excited Electronic States ◽  
Theoretical Approaches ◽  
Small Clusters

A brief report is presented of recent advances in the theoretical study of clusters and fullerenes with ab-initio methods. Selected calculations of structural properties, excited electronic states and vibrational spectra will be discussed. The purpose is to compare different methods and clarify their specific powers and weaknesses.

Gas phase ion chemistry and ab initio theoretical study of phosphine. III. Reactions of PH2+ and PH3+ with PH3

2000 ◽  
Vol 112 (4) ◽  
pp. 1814-1822 ◽  
Author(s):  
Paola Antoniotti ◽  
Lorenza Operti ◽  
Roberto Rabezzana ◽  
Glauco Tonachini ◽  
Gian Angelo Vaglio
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Ion Chemistry ◽  
Gas Phase Ion Chemistry ◽  
Gas Phase Ion

Possible gas-phase ion pairs in amine-HCl complexes. An ab initio theoretical study

1984 ◽  
Vol 110 (5) ◽  
pp. 464-468 ◽  
Author(s):  
Zdzisław Latajka ◽  
Shogo Sakai ◽  
Keiji Morokuma ◽  
Henryk Ratajczak
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Ion Pairs ◽  
Gas Phase Ion
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