Detail of "18295-52-8"

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Excited-state properties and environmental effects for protonated Schiff bases: a theoretical study

All Rights Reserved. Excited-state properties and environmental effects for protonated Schiff bases: a theoretical study. Aquino, Adelia J. A.; Barbatti, Mario; Lischka, Hans (Institute for Theoretical Chemistry, University of Vienna, Vienna 1090, Austria). ChemPhysChem, 7(10), 2089-2096 (English) 2006 Wiley-VCH Verlag GmbH & Co. KGaA. CODEN: CPCHFT. ISSN: 1439-4235.Several reagents with their cas registry numbers 28963-72-6 and 18295-52-8 are used here. DOCUMENT TYPE: Journal CA Section: 22 (Physical Organic Chemistry) Section cross-reference(s): 6 Complete active space SCF (CASSCF), multireference CI (MRCI), d. functional theory (DFT), time dependent DFT (TDDFT) and the singles and doubles coupled-cluster (CC2) methodologies have been used to study the ground state and excited states of protonated and neutral Schiff bases (PSB and SB) as models for the retinal chromophore. Systems with two to four conjugated double bonds are investigated. Geometry relaxation effects are studied in the excited pp* state using the aforementioned methods. Taking the MRCI results as ref. we find that CASSCF results are quite reliable even though overshooting of geometry changes is obsd. TDDFT does not reproduce bond alternation well in the pp* state. CC2 takes an intermediate position. Environmental effects due to solvent or protein surroundings have been studied in the excited states of the PSBs and SBs using a water mol. and solvated formate as model cases. Particular emphasis is given to the proton transfer process from the PSB to its solvent partner in the excited state. It is found that its feasibility is significantly enhanced in the excited state as compared to the ground state, which means that a proton transfer could be initiated already at an early step in the photodynamics of PSBs. .

Theoretical studies on the conformational preferences of 1,3-diazabuta-1,3-dienes

Theoretical studies on the conformational preferences of 1,3-diazabuta-1,3-dienes. Kumar, R. Senthil; Marwaha, Alka; Bharatam, Prasad V.; Mahajan, Mohinder P. (Department of Applied Chemistry, Guru Nanak Dev University, Amritsar 143005, India). THEOCHEM, 640, 1-12 (English) 2003 Elsevier Science B.V. CODEN: THEODJ. ISSN: 0166-1280. DOCUMENT TYPE: Journal CA Section: 22 (Physical Organic Chemistry) Ab initio MO and d. functional calcns. have been performed to study the conformational preferences for 1,3-diazabuta-1,3-dienes. Complete optimizations using B3LYP/6-31G level on HN:CH-N:CH2 indicate that the conformational preferences are different for the E and Z isomers, E preferring s-cisoid arrangement and Z preferring s-trans arrangement. 18295-52-8 and 74830-81-2 are cas registry numbers of chemicals which are used as reagents here. Natural Bond Order anal. has been carried out on the various conformations of 1,3-diazabuta-1,3-dienes to understand the electron delocalizations and the origin of conformational preferences in these systems. To understand the effect of substituents on conformations, complete optimizations have been carried out with Me, SH, and NH2 substituents at C-2 and C-4 positions. The results indicate that the s-cisoid structure is more stable in most cases and in some cases the s-trans even does not exist. A systematic change in the N1-C2-N3-C4 torsional angle is obsd. as a function of the electron delocalization in these systems. The s-cisoid structure tends to be closer to s-cis in the E isomers and such an effect has not been obsd. in the Z isomers. The preference for the s-trans arrangement and the f values in E-s-cisoid structure are larger in solvent media. .