Search results for "Taut"

Proton tautomerism in 2-nitramino-C-nitropyridine derivatives - Experimental and quantum chemical study

2019

Abstract The structures of 2-nitramino-3-nitropyridine and 2-nitramino-5-nitropyridine have been characterized by X-ray diffraction and Density Functional Theory (DFT) studies. In the crystals, both compounds exist as the imino forms. The DFT calculations were performed in order to explore the amino-imino tautomerism of the studied compounds in the gas phase and the influence of solvent polarity on the tautomeric equilibrium. The Harmonic Oscillator Model of Aromaticity index (HOMA) and Nucleus Independent Chemical Shift (NICS) calculated for the pyridine rings of the studied systems, demonstrated a noticeable decrease in aromaticity of the imino forms. This study showed also that the highe…

Experimental and theoretical push-pull Chemo- and regioselectivity in 1,3-Dipolar cycloaddition reactions: the case of benzotriazepin-5-one with mesi…

2007

A novel heterocyclic compound 3-mesityl-5-methyl-4,5,11,11a-tetrahydro-6H-[1,2,4]oxadiazolo [5,4-b][1,3,4]benzotriazepin-6-one 4 has been synthesised by a 1,3 dipolar cycloaddition (13DC) reaction of 1,3,4-benzotriazepin-5-one 1 with mesitylnitrile oxide 3. The reaction, beside its synthetic interest, has shown to be completely chemo- and regioselective. The structure of the compound was determined by X-ray crystallography and analysed by spectral methods (NMR and mass spectrometry). The molecular mechanism for the reaction has been studied using quantum mechanical calculations at the B3LYP/6-31G* theory level. Two mechanisms are possible for the formation of the cycloadduct 4. The first on…

The azide/tetrazole equilibrium: an investigation in the series of furo- and thieno[2,3-e]tetrazolo[3,2-d]pyrimidine derivatives

2016

Abstract Starting from 7(8)-chlorofuro(thieno)[3,2- d ]pyrimidines 1 , the corresponding 7(8)-hydrazinofuro(thieno)[3,2- d ]pyrimidines 2 were obtained by reaction with hydrazine. By treatment with nitrous acid, compounds 2 gave fused furo- and thieno[2,3- e ]tetrazolo[1,5- c ]pyrimidines 3 T and 4 T in excellent yields, which in solution exist in equilibrium with 7(8)-azidofuro(thieno)[3,2- d ]pyrimidines 3 A and 4 A . Compounds 3 T / 3 A and 4 T / 4 A represent useful substrates for investigating the azide/tetrazole equilibrium: it has been examined as a function of solvent, temperature, and their structure. We have observed that, in solution, in both 3 and 4 the equilibrium was strongly …

Latvija. Pārskats par tautas attīstību 2017/2018: Sabiedriskā labuma radīšana un kolektīvo resursu nosargāšana Latvijā

2019

Ziemeļkorejas ekonomiskās attiecības un to ietekme uz politiskajām attiecībām

2019

Bakalaura darba tēma ir Ziemeļkorejas ekonomiskās attiecības un to ietekme uz politiskajām attiecībām. Šī bakalaura darba ietvaros tiek pētītas Ziemeļkorejas bilateriālās ekonomiskās attiecības ar Ķīnu, Krieviju un Indiju, kā arī tiek apskatīts, vai ar ekonomisko partnerību ir iespējams ietekmēt Ziemeļkorejas politisko rīcību. Darba teorētiskajā sadaļā tiek aplūkotas savstarpējās atkarības attiecības no starptautiskās politekonomijas perspektīvas. Darba mērķis ir noskaidrot Ķīnas, Krievijas un Indijas spējas izmantot ekonomiskās attiecības ar Ziemeļkoreju, lai ietekmētu tās politisko rīcību no 2008. gada līdz 2018. gadam. Darbā tiek izvirzīts pētnieciskais jautājums: kādai ir jābūt ekonomis…

Zvaigžņotā Debess: 2004/05, Ziema

2004

Contents: Ņ.Ozoliņa. Earthquakes in Latvia ; I.Daube. Space Craft “Ranger-7” ; M. Gailis. Moon Investigation in Riga ; J.Tambergs. Problems of Dialogue between Quantum Mechanics and Theology (concluded) ; Z Alksne, A.Alksnis. Ultra-Cool Dwarf Pair Weighed ; A.Balklavs. Successful Hunt of Protostars ; A.Balklavs. Silhouette of a Black Hole ; A.Balklavs. A Distant Giant Quasar ; A.Balklavs. Cosmic Objects in Captivating Photos – 3 ; J.Freimanis. Extragalactic Planetary Nebulae ; J.Jaunbergs. Cassini Enters the Saturnian System ; D.Krieviņš. Space Launchers of Early XXI Century. The Commonwealth of Independent States (CIS) ; J.Bārzdiņš. Professor Rusins-Martins Freivalds on the Path of Science…

1,4-Benzoquinones with Styryl Substituents

2002

2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4π + 2π] cyclodimerization reactions. Chemo-, regio- and stereoselective processes lead to dimers (compounds 1−10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 ⇄ 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4π + 2π] cycloaddition (10 ⇄ 11). The same selective [4π + 2π] cyclodimerization can be observed in solution upon irradiation (e.g., 1a ⇄ 10a), in contrast to irradiation in the crystalline state which yields a […

Life-Space Mobility in Parkinson's Disease: Associations with Motor and Non-Motor Symptoms.

2019

Background To describe life-space mobility and explore associations of motor and non-motor symptoms with life-space mobility in people with Parkinson’s disease (PD). Methods About 164 community-dwelling persons with PD (mean age 71.6 years, 64.6% men) received a postal survey and a subsequent home visit. Motor assessments included perceived walking difficulties (Walk-12G), mobility (Timed Up and Go test), motor symptoms (UPDRS-III), and freezing of gait (item 3, FOG-Qsa). Non-motor symptoms included depressive symptoms (GDS-15), pain, fatigue (NHP-EN), and global cognition (MoCA). Life-space mobility was assessed with the life-space assessment (LSA). Calculations included composite score (r…

Syntheses with organoboranes. Part 14: Enolization–aldolization of conjugated cyclohexenones via dienolborinates

2002

Abstract Enolization of cyclohex-2-enone ( 1 ), 3-methyl- ( 2 ), 3,5-dimethyl- ( 3 ), 3,5,5-trimethyl- ( 4 ), and 3,4,5,5-tetramethylcyclohex-2-enone ( 5 ) with chlorodicyclohexylborane proceeds by deprotonation at the 6-position. Aldolization of the dienolborinates with benzaldehyde, and acetaldehyde, provides the corresponding anti aldols with 87–95% selectivity. Ketones 4 and 5 undergo competitive deprotonation at the 3-methyl group and aldolization at the 2-position. In contrast, lithium dienolates derived from 4 and 5 gave syn aldols with 95% selectivity.

Can peer-tutored psychological flexibility training facilitate physical activity among adults with overweight?

2021

Objective An increase in psychological flexibility has been found to be associated with health behavior changes. Peer-led interventions have been advantageous in improving physical activity among individuals at health risk. This study aimed to discover whether an ACT-based peer-tutored online intervention can increase self-reported physical activity participation and psychological flexibility among adults with overweight. Design The study was a non-randomized longitudinal intervention study. The intervention participants (N = 177) were primary health care clients with overweight. They participated in a 24-month program provided by health services, including three online modules of ACT of si…