The six-membered cyclic allenes given in the title have been studied theoretically by means of an MR-CI approach. For all compounds, the allene structures were found to be the ground states in the gas phase. In the cases of cyclohexa-1,2-diene (1), the isobenzene 2, and the isonaphthalene 7, the most stable structures having a planar allene moiety are the diradicals 1b, 2b, and 7b, representing the transition states for the racemization of 1a, 2a, and 7a and being less stable than the latter by 14.1, 8.9, and 11.2 kcal/mol, respectively. At variance with this order, the 3delta(2)-pyran 4 and the chromene 5 have the zwitterions 4c and 5c as the most stable planar structures, which lie only 1.0 and 5.4 kcal/mol above 4a and 5a, respectively. According to the simulation of the solvent effect, 4c even becomes the ground state of 4 in THF solution. The frontier orbitals of the respective states of 2 and 4 suggest different rates and sites for the reaction with nucleophiles. For the first time, the pyran 4 has been generated and trapped. As a precursor for 4, 3-bromo-4H-pyran (9) was chosen, the synthesis of which was achieved on two routes from 4H-pyran. The treatment of 9 with potassium tert-butoxide (KOt-Bu)/18-crown-6 gave 4-tert-butoxy-4H-pyran as the only discernible product, whether styrene or furan was present, indicating the interception of 4 by KOt-Bu. Finally, the disagreement between the experiment and the theory concerning the heat of formation and the electronic nature of the isobenzene 2 is resolved by demonstrating that the experimental data can provide only an upper limit of the DeltaH(f) degrees value.

Carbon-13 spectra of 27 peptides have been obtained by high-resolution nmr spectroscopy with the aid of proton decoupling. The chemical shifts of the different amino acid moieties are found to have systematic deviations from those of the free zwitterionic amino acids. These effects depend very largely on the position of an amino acid in a peptide, i.e., on whether it is a C-terminal, an N-terminal, or a nonterminal unit, but not on the nature of its neighbors in the chain, unless one of these is proline. The results have substantial value for the determination of amino acid sequences in di-and tripeptides. Prolonation and deprotonation of zwitterionic peptides have considerable effects on the chemical shifts which are, for the most part, limited to the amino acid units directly involved in the reaction. The one important exception to this rule that we have observed is interpreted as being the consequence of a conformational change which the peptides undergo when transformed from the zwitterion to the anion or cation.N umerous publications in recent years emphasize the potential of nmr investigations on amino acids, peptides, and proteins. 3 The application of proton nmr to proteins, however, was shown to be limited because of the large number of different types of protons in a protein combined with a relatively small spread in chemical shifts and large intrinsic line widths. Specific deuteration of proteins results in much simpler proton spectra and allows more detailed studies. The carbon-13 (cmr) spectra of amino acids 4 show much larger chemical shift differences than for the corresponding proton spectra. This fact provides promise with regard to the resolution of specific resonances in the spectra of peptides and proteins. Several recent papers offer results in accord with this prediction. 5 -9 Proteins with specifi.cally labeled carbon-13 amino acids can now be confidently expected to provide detailed information concerning the three-dimensional structure of proteins in solution and interactions of protein with small molecules.We report here the results of a systematic cmr investigation carried out on small peptides with 1 3 C of natural abundance. The objective of this study was to see if cmr spectroscopy could be developed to be useful for the determination of the amino acid sequences in di-and tripeptides, particularly through possible pH dependences of the carbon chemical shifts. , Fellow, 1970, Fellow, -1971 (3) For a review, see G. C. K. Roberts and 0. Jardetzky, Adcan. Protein Chem., 24, 447 (1970 227, 840 (1970).(6) A. Allerhand, D. Doddrell, V. Glushko, D. W. Cochran, E. Wenkert, P. J. Lawson, and F. R. N. Gurd, J. Amer. Chem. Soc., 93, 544 (1971). (7) A. Allerhand, D. W. Cochran, and D. Doddrell, Proc. Nat. Acad.Sei. U. S., 67, 1093 (1970).(8) G. Jung, E. Breitmaier, and W. Voelter, Angew. Chem., lnt. Ed. Eng/., 9, 894 (1970). (9) 42, 1148 (1971). Experimental SectionThe peptides examined in the present research were all commercial materials and were used without further purificat...

Die Konkurrenz von Dipolarophilen‐Paaren um Benzonitriloxid,. In situ aus Benzohydroximoylchlorid (4) freigesetzt, ergab die sich über 4 Zehnerpotenzen erstreckenden relativen Additionskonstanten von 39 Dipolarophilen. Benzonitriloxid gehört zu den 1,3‐Dipolen, die sowohl mit elektronen‐armen als auch mit elektronen‐reichen Mehrfachbindungen rascher reagieren als mit gewöhnlichen Alkenen und Alkinen. Die Kombination mit den bekannten Orientierungsverhältnissen erbrachte partielle Geschwindigkeitskonstanten der beiden Additionsrichtungen. Die Additivität der Substituenten‐Beiträge zur freien Aktivierungsenergie ist nur näherungsweise erfüllt. — Die spezifische Dipolarophilen‐Skala des Benzonitriloxids sowie die Orientierungsphänomene werden im Lichte neuer MO‐störungstheoretischer Behandlungen von Sustmann und Houk diskutiert. Die Aktivitätssequenz wird mit denjenigen des Diphenylnitrilimins und des N‐Methyl‐C‐phenylnitrons verglichen.

Elngegdngen dm 9 Mdi 1971Aufgrund der Umsetzungen von siebzehii Nitriloxideii mit fiiiif c&ungesattigten Carbonsaureestern ivird der EinfluR von Substituentcn in1 1,3-Dipol auf die lsomerenverteilung im Produkt, d. h. also auf das VerhPltnis der beiden Additionsrichtungen, studiert. Das Orientierungsverhaltcn wird im wesentlichen von der elektronischen Struktur des Nitriloxid-Systems dikticrt und nur untergeordnet vom Substituenten beeinfluat. Energetisch gesehen, bewegen sich die Substituenten-Effekte hei den fiinf Modell-Dipolarophilen zwischcn AAG+ 0.8 und 2.0 kcal/mol. Dcr FInfluR der Substituenten auf die konkurrierenden Richtungen der [,4, -; ,2,]-Cycloadditioncn wird in1 Rahmen des Houkschen Ansatzes der MO-Storungs-theorie6) diskutiert; xterischc F,ffckte uberlagern sich den elektronischen. ~-Simtliche Addukte werden analytisch und durch N M R-Spektren charakterisiert. Die Substituenten-Einflusse auf T-und J-Werte der Ringprotonen von 2-Isoxazolincn und Isoxazolen werden ermittelt. 1,3-Dipolar Cycloadditions, 74 I) Orientation Phenomena in Cycloadditions of Aliphatic and Aromatic Nitrile Oxides to a#-Unsaturated Carboxylic Esters *)The additions of seventccn nitrilc oxides to five a,$-uiisaturated carhoxylic esters have been studied to determine the influence of a suhstjtuent in the 1,3-dipolc on the isomer distribution in the product, Lr., on the ratio of the two directions of addition. The regiochemistry is mainly dictated by the electronic structure of the nitrile oxide system, and is influenced only to a minor extent by suhstituents. The suhstituent effects mcasured for the five model dipolarophiles, energywise, are bctween aaC* == 0.8 and 2.0 kcal/mole. Thc influence of suhstituentg is discussed within Houk's MO perturbation treatments) ; steric effects are superimposed. ~ All adducts have been characterircd by analyses and n.m.r. spectra. The influences of substituents on T and J values of the ring protons of 2-isoxazolines and isoxazoles have been determined.Die Cycloadditionen von ru'itriloxiden an hindungsunsyininetrische olefinische und acetylcnische Dipolarophile zeigeii cine charakteristische Regioselektivitit4), deren Verstindnis 1) 73. Mitteil.. K. Bast, M . Chrrrtl, R. Hursgen und W. Mach, Chem. Ber. 106, 3312 (1973), 2 ) Teilweise Kurzveroffcnthchung . M . Chrrstl und R Hursgrn, Tetrahedron Lctt. 1968, 5209. 3 ' Aus der Dusertat. M Christl, LJIIIV. Munchen 1969, sowe Versuche 1969/70 4) Uhersicht C. Crundnzunn und P . Grunanger, The Nitrile Oxides, S. 96 119, Tab. XXVIII, vors tehend. XXIX, Springer-Verlag, Berlin-Heidclberg-New York 1971 M . Christl und R. Huisgeii Jahrg. 106erst die storungstheoretische Behandlung 1,5,6) anbahnt. Monosubstituierte Athylene und Acetylene treten mit Benzonitriloxid zu 5-substituiertcn Tsoxazolinen und lsoxazolen zusammen, gleichgultig, ob es sicli urn elektroiien-anziehende oder elektronen-liefernde Substituenten handelt ; iiur in wciiigcn Fallen erschien der Substituent untergeordnet auch in der 4-Stellung 7.8).Alinliche Verhaltnisse fand man beim Dipheny...

Durch Reduktion von Benzvalen (1) mit Diimin wird das Tricyclo[3.1.0.0~~6]hexan (3) in guter Ausbeute erhalten. Das Verfahren macht das bereits von Lemal und Shim dargestellte 3 erheblich leichter und in groBeren Mengen zuganglich. 1H-und 13C-NMR-spektroskopische Daten werden diskutiert. Sowohl die thermische als auch die AgBF4-katalysierte Umlagerung von 3 fuhrt zu 1,3-Cyclohexadien (8). -Die Ozonolyse von 1 mit anschlieBender LiAIH4-Reduktion ergibt das cis-l,3-Bis(hydroxymethyl)cyclobutan (13a). Diimine Reduction and Ozonolysis of BenzvaleneVia reduction of benzvalene (1) with diimine tricyclo[3.1.0.02~6]hexane is obtained in good yield. The procedure renders 3, which has already been synthesized by Lemal and Shim, accessible much easier and in larger quantities. * H and 13C n.m.r. spectroscopic data are discussed. Both the thermal and the AgBF4-catalyzed rearrangement of 3 yield 1,3-cyclohexadiene (8). -The ozonolysis of 1 with subsequent LiAlH4-reduction results in cis-1,3bis(hydroxymethy1)cyclobutane (13a).