摘要:

AbstractSolutions of tétracyanoéthylène and nine mono‐ and di‐para‐substituted stilbene derivatives(XH, CH3, MeO, Cl, Br, NO2) show two charge transfer bands in the UV visible spectrum range, associated with two molecular complexes I and II. The position of the first band around 17000 cm−1is highly dependent on the substituent, whereas the position of the second band is almost constant about 26000 cm−1(except for the complex of 4,4′‐dimethoxystilbene).These two bands are assigned to the transitions from the two highest occupied molecular orbitals of the donors, calculated by the method ofHuckel.Taking account of the symmetries of the stilbènes and tétracyanoéthylène molecular orbitals, two most probable configurations are proposed for these molecular complexes, I and II, and one in particular for the 4,4′‐dimethoxy derivative. The determination of the differences in formation enthalpy, ΔΔH, for these two complexes I and II, experimentally confirms the particular behaviour o

ISSN:0165-0513    

DOI:10.1002/recl.19750940802

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractOptical resolution ofDL‐homohistidine could be effected by fractional crystallization of the diastereomeric hydrogen tartrates. Starting fromL‐glutamic acid, the direct synthesis ofL‐homohistidine was accomplished through a ten‐stage synthesis requiring the isolation of only six interm

ISSN:0165-0513    

DOI:10.1002/recl.19750940803

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractProton NMR spectra ofcis‐Pt(Bu2dtc)2I2show, between −100 and + 100°C, two triplets of the α‐protons, even at 220 MHz no further splitting of the triplets could be observed. At about 100°C both triplets coalesce to a single one due to an intramolecular process (ΔH≠= 7.2 kcal/mole and ΔS≠= −37 eu). The proton NMR spectrum ofcis‐Pt(MeBzdtc)2I2shows two signals for both the methyl and methylene protons; at about 100°C both doublets coalesce to singlets. The possible intramolecular processes were studied with a complete permutational analysis. The experimental data can be explained by assuming a slow exchange up to 100°C, then a fast racemisation process starts in which a heteropolar breaking of a Pt‐ligand bond is involved.The isomerization oftrans‐ intocis‐Pt(Bu2dtc)2I2was studied between −10° and + 35°C by proton NMR The activation parameters ΔH≠= 17.2 kcal/mole and ΔS≠= −17 eu suggest an ionic interm

ISSN:0165-0513    

DOI:10.1002/recl.19750940804

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractThe uncertainty about the constitution of the vapour of selenium trioxide has been settled. It is concluded that only tetramer molecules are present. A new value for the heat of sublimation has been found: 17.7 ± 0.8 Kcal/mole Se4O12, as well as for the heat of evaporation: 15.4 ± 0.2 Kcal/mole Se4O1

ISSN:0165-0513    

DOI:10.1002/recl.19750940805

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractThe rate of the reaction of methyl chloride and silicon, copper functioning as a catalyst and zinc and aluminium as promoters, has been measured with a calorimeter. From the experimental results it follows that the calorimeter can be used to study the kinetics of the direct synthesis of methylchlorosilanes. At a temperature of 333°C and at pressures of 300–800 Torr the initial reaction rate can be described by the power functionr = k Pn, withn, the order of the reaction with respect to methyl chloride, being equal to 0.

ISSN:0165-0513    

DOI:10.1002/recl.19750940806

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractSeveral poly‐unsaturated, conjugated ketene acetals (Table I) have been obtained by 1,2‐ or 1,4‐elimination of alcohol with potassium amide from unsaturated acetals or ortho‐esters having hydrogen in an allylic position. The products have properties similar to simple electron‐rich olefins as is apparent from their smooth addition reactions with

ISSN:0165-0513    

DOI:10.1002/recl.19750940807

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractThe cyclization of hydroxyallyl ions (protonated 3‐alken‐2‐ones) to tetrahydrofuryl ions in a series of strong acids (HF, H2SO4, FSO3H) and superacids (FSO3HSbF5, HFSbF5) has been studied, together with some related reactions. The rates of cyclization of hydroxyallyl ions increase with substitution of alkyl groups at the C(5) carbon; they pass through a maximum if the acidity of the solvent is increased. It is concluded that the cyclizations involve concerted reactions, the formation of any distinct (short‐lived) intermediates taking place only when particular combinations of acidity of the solvent and structure of the starting ion are present.Rate constants are also reported for thecis/transisomerization of protonated 3‐penten‐2‐one. Protonated 4‐penten‐2‐one isomerizes to the hydroxyallyl ion,viasolvent addition products as long‐lived intermediates, but protonated 4‐hexen‐2‐one gives the cyclized ion even under conditions of kinetic control. The acid‐catalysed ionization of protonated 5‐chloropentan‐2‐one gives a hydroxyallyl ion as the first product. All these reac

ISSN:0165-0513    

DOI:10.1002/recl.19750940808

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractTreatment of 3‐(methylthio)‐1,2,4‐triazine with potassium amide in liquid ammonia gives 3‐amino‐1,2,4‐triazine, 3,3′‐bis(methylthio)‐5,5′‐bi‐1,2,4‐triazine and 3‐amino‐3′‐(methylthio)‐5,5′‐bi‐1,2,4‐triazine. In the 3‐amino compound formed from 3‐(methylthio)‐[4‐15N]‐1,2,4‐triazine, 93% of the15N is present in theexocyclicnitrogen of the amino group. A SN(ANRORC) mechanism i

ISSN:0165-0513    

DOI:10.1002/recl.19750940809

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

Abstract13CNMR data (shifts and relaxation times) show that the conformational equilibrium and the intramolecular mobility of squalene are very similar in media of different polarity. This is inconsistent with one ofvan Tamelen'soriginal proposals explaining the selective terminal epoxidation in terms of tight coiling of squalene in polar media. MINDO/2′ calculations predict that terminal epoxidation is favoured over internal epoxidation by ∼1.5 kcal

ISSN:0165-0513    

DOI:10.1002/recl.19750940810

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19750940801

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY