摘要:

AbstractThe crystal structure of the title compound (orthorhombica= 26.724,b= 10.899,c= 9.483 Å, space groupPna21,Z= 12) has been determined by X‐ray analysis. The structural units consist of hydrogen‐bonded trimers with approximateC3hsymmetry. The results are discussed in relation to theBeckmannrearrangement of the title compound, which yields exclusively the mirror‐symmetric d

ISSN:0018-019X    

DOI:10.1002/hlca.19760590502

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractA stereoselective synthesis of (±)‐abscisic acid (7) is described in which 2‐cis3‐methylpent‐2‐en‐4‐yn‐1‐ol (2) is used to introduce the 2‐

ISSN:0018-019X    

DOI:10.1002/hlca.19760590503

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Abstractp‐Nitrobenzenediazonium tetrafluoroborate dissolved in dimethylsulfoxide (DMSO) at 50° formsp‐nitrophenol in 88–90% yield. The phenolic oxygen atom originates exclusively from the oxygen atom of DMSO as demonstrated by the use of18O‐labelled DMSO. The first‐order rate of dediazoniation is the same under N2as it is in the presence of air. The rate is little influenced by the addition of benzene or iodobenzene. However, the products formed in the presence of these additives are significantly different. UV. spectra and the reactivity of diazonium salt solutions in DMSO when mixed with reagents in aqueous solution demonstrate that a relatively stable charge‐transfer complex is formed between the diazonium ion and DMSO. The product analyses and the kinetic and spectral results of dediazoniation in DMSO with and without additives are consistent with a mechanism in which the rate‐limiting step is the formation of ap‐nitrophenyl radical from the charge‐transfer complex.p‐Nitrophenol and the products with benzene and iodobenzene are formed in subsequent fast competition steps. In the presence of small amounts of pyridine the dediazoniation is much faster and follows a different kinetic law. Pyridine effectively competes with DMSO in the reaction

ISSN:0018-019X    

DOI:10.1002/hlca.19760590504

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe mechanism of dediazoniation of arenediazonium tetrafluoroborates in 2,2,2‐trifluoroethanol (TFE) is strongly dependent on the concentration of added pyridine. The added base complexes with the diazonium ion and diverts it to a homolytic pathway. Complex formation is indicated by the disappearance of the\documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus \equiv {\rm N}\raise1pt\hbox{---}$\end{document}stretching vibration and appearance of a new band at about 1640–1690 cm−1ascribed to the\documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} {\rm N}\raise1pt\hbox{=\kern-3.45pt=} {\rm N}\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus {\rm C}_5 {\rm H}_5$\end{document}system. UV. and NMR. results support this conclusion.Chemically induced dynamic nuclear polarization (CIDNP) experiments clearly implicate a radical‐pair as an important intermediate in the decomposition of these co

ISSN:0018-019X    

DOI:10.1002/hlca.19760590505

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe complexation of 1‐methyl‐2‐hydroxymethyl‐imidazole (L) with Cu(I) and Cu(II) has been studied in aqueous acetonitrile (AN). Cu(I) forms three complexes, Cu(AN)L+, CuL2+, and Cu(AN)H−1L, with stability constants logK(Cu(AN)++ L ⇌ Cu(AN)L+) = 4.60 ± 0.02, logβ2= 11.31 ± 0.04, and logK(Cu(AN)H−1L+H+⇌ Cu(AN)L+) = 10.43 ± 0.08 in 0.15MAN. The main species for Cu(II) are CuL2+, CuH−1L+, CuH−1L2+, and CuH−2L2.The autoxidation of CuL2+was followed with an oxygen sensor and spectrophotometrically. Competition between the formation of superoxide in a one‐electron reduction of O2and a path leading to H2O2viabinuclear (CuL2)2O 22+was inferred from the rate law\documentclass{article}\pagestyle{empty}\begin{document}$${{ - {\rm d}\left[{{\rm O}_2 } \right]} \mathord{\left/ {\vphantom {{ - {\rm d}\left[{{\rm O}_2 } \right]} {{\rm dt}}}} \right. \kern-\nulldelimiterspace} {{\rm dt}}} = \left[{{\rm CuL}_2^ + } \right]^2 \left[{{\rm O}_2 } \right]\left({\frac{{k_{\rm a} }}{{1 + k_{\rm b} \left[{{\rm CuL}^ + } \right]}} + \frac{{k_{\rm c} \left[{\rm L} \right] + k_{\rm d} + {{\left({{{k_{\rm f} } \mathord{\left/ {\vphantom {{k_{\rm f} } {\left[{\rm L} \right]}}} \right. \kern-\nulldelimiterspace} {\left[{\rm L} \right]}} + k_{\rm g} + k_{\rm h} \left[{\rm L} \right]} \right)} \mathord{\left/ {\vphantom {{\left({{{k_{\rm f} } \mathord{\left/ {\vphantom {{k_{\rm f} } {\left[{\rm L} \right]}}} \right. \kern-\nulldelimiterspace} {\left[{\rm L} \right]}} + k_{\rm g} + k_{\rm h} \left[{\rm L} \right]} \right)} {\left[{{\rm H}^ + } \right]}}} \right. \kern-\nulldelimiterspace} {\left[{{\rm H}^ + } \right]}}}}{{\left[{{\rm CuL}_2 ^ + } \right] + k_{\rm e} \left[{{\rm Cu}\left({{\rm II}} \right)} \right]_{{\rm tot}} }}} \right)$$\end{document}withka= (2.31 ± 0.12) · 104M−2S−1,kb= (1.0 ± 0.2) · 103M−1,kc= (2.85 ± 0.07) · 102M−2S−1,kd= 3.89 ± 0.14M−1S−1,ke= 0.112 ± 0.004,kf= (2.06 ± 0.24) · 10−10M S−1,kg=

ISSN:0018-019X    

DOI:10.1002/hlca.19760590506

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe photoelectron (PE.) spectra of azuleno[l, 2, 3‐cd]phenalene (1) and azuleno‐ [5,6,7‐cd]phenalene(2) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a2, 6b1, 5b1, 3a2and 4blorbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model.The UV./VIS. polarized absorption spectrum of1in the region 10000–45000 cm−1has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP‐CI method.A comparison between the electronic structures of1and2is made by means of a si

ISSN:0018-019X    

DOI:10.1002/hlca.19760590507

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe direct irradiation of the monomethoxybarrelene8gives cyclooctatetraene product18(Φ = 0.075)viatheanti‐Epiotis aromatic‐vinyldiester [2π+2π] bridging route, and two semibullvalenes16(Φ = 0.075) and17(Φ = 0.075) from di‐π‐methane rearrangements initiating from vinyl‐vinyldiester bridging. Benzophenone sensitization yields16(Φ =0.11) and17(Φ = 0.11). The dimethoxybarrelene9gives only semibullvalene10, this resulting from di‐π‐methane rearrangement involving the vinyl and vinyldiester bridges, upon direct (Φ = 0.009) or benzophenone sensitized irradiations (Φ = 0.38).10undergoes a vinylcyclopropane rearrangement to give semibullvalene11upon direct or acetone sensitized

ISSN:0018-019X    

DOI:10.1002/hlca.19760590508

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe crystal structure of an iodo‐derivative of cyclosporin A has been determined in order to elucidate the constitution of this cyclic undecapeptide. Crystals of iodocyclosporin A are monoclinic,a= 10.475(5),b= 19.60(1),c= 21.04(1) Å, β 99.35(2)°, space groupP21(C 22, No. 4). The structure was solved by the heavy atom method and refined by block‐diagonal least‐squares analysis to a finalR‐factor of 0.135 with hydrogen atoms in calculated positions. The cyclic peptide has a conformation which is partly β‐pleated sheet and partly open loop. The structure analysis demonstrates for the first time the reality of a new type of dipeptide hydrogen‐bonding, predicted byPullmanfrom MO calculations and leading to a conformation describ

ISSN:0018-019X    

DOI:10.1002/hlca.19760590509

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Synthesis of human insulin. II. Preparation of the A(1–13) fragment.The present report gives a detailed account of the synthesis of the protected tridecapeptide A(1–13), BocGlyIleValGlu(OBut)Gln Ser(But)LeuOH (20), an essential intermediate in the recently published total synthesis of human insulin [1]. The main feature in the synthesis of20was the specific formation of a disulfide bond between A6 and A11 in the presence of an additional cysteine residue (A7). The selective ring closure was accomplished with the segment A(6–13), HCys(Trt)Cys(Acm)Thr(But)Ser(But)IleCys(Trt)Ser(But)LeuOH (18), which was obtained by way of conventional synthesis routes. Treatment of18with iodine in trifluoroethanol formed the desired disulfide bridge from the twoS‐trityl‐cysteine residues without affecting theS‐acetamidomethyl‐protected cysteine A7. A final azide coupling with theN‐terminal derivative A(1–5) (3) provided the t

ISSN:0018-019X    

DOI:10.1002/hlca.19760590510

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe formation of Pd(II) complexes with aminopolycarboxylate anions has been investigated using pH and UV.‐spectrophotometric measurements at ionic strength 1Mand 20°. In some cases bromide or thiocyanate ions have been used as auxiliary ligands. Pd2+forms the strongest complexes of the hitherto investigated divalent metal ions. The stability constants are discussed in relation to the particular stereochemistry of Pd(II) complex

ISSN:0018-019X    

DOI:10.1002/hlca.19760590511

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY