Influence d'un ou de plusieurs groupements tertiobutyle sur le comportement magnétooptique du doublet libre d'un atome de phosphore tricoordonné

A magnetooptical study of some halogenotertiobutylphosphines is performed in order to improve the so-called regular relationship which seemed to exist between the magnetic rotation, ?dP, of the lone pair and the bond angles in PX₃ compounds. It is clearly shown that, in any case, ?dP is largely lower than the extreme value which was observed in PX₃ molecules for which XPX=100°. Thus, the existence of the previously invoked relationship vanishes and the question remains as to why there exists a maximum of ?dP for XPX of 100°.     

Peptides—XXXV: Synthesis of the 17–26 fragment of a lysozyme analogue

The fully protected 17–26 fragment of a lysozyme analogue has been synthesised. A fragment condensation approach has been employed using the protected subfragments 17–19, 20–22 and 23–26. In the synthesis of the subfragments the use of the diphenylphosphinyl mixed anhydride method has been demonstrated.     

Peptides—XXXVI: Synthesis of the 27–37 fragment of a lysozyme analogue

Two syntheses of the fully protected 27–37 fragment have been carried out. The results indicate that coupling of the 27–32 and 33–37 fragments is superior to the alternative 27–29 plus 30–37 approach.     

The determination of nitrite and nitrate by the ring-oven technique

Determinations of nanogram amounts of nitrite and nitrate individually and together, based on a variation of the ring-oven technique, are described. In the “segment technique” used, a stable standard scale is not necessary. Interferences have been studied. Nitrite in sausages can be determined.     

Peptides—XXXXIV: Synthesis of the 105–117 fragment of a lysozyme analogue

The synthesis of the (105–117) fragment of a Lysozyme analogue is described. This sequence was assembled by DCCl/HONSu fragment coupling of the (105–111) and (112–117) subfragments which were both constructed by the fragment coupling method. The arginine residue at position 114 was initially unprotected but ultimately protection was afforded by the use of the adamantyloxycarbonyl group.     

The 9-barbaralyl cation, 1,4-bishomotropylium ion and some related C9H9 carbocations : Electronic structures, stability and reactivity

The electronic structures of the 9-barbaralyl cation(1), the 1,4-bishomotropylium ion (5) and some related C₉H₉⁺ isomers have been studied byab initio STO-3G calculations. The stability of the cyclopropylcarbinyl cation 1 and the homoaromatic ion 5 as compared with their allylic counterparts is explained in terms of delocalization and MO interactions between molecular fragments. Both the symmetry of, and the distance between, molecular fragments are of importance for the electronic structure, and even symmetry-allowed interactions are negligible in the absence of favourable geometrical distortions. The non-classical ion 3 with D_3h symmetry presents special problems where other factors, such as strain, are important for the total energy. A choice between proposed mechanisms for the degenerate rearrangements of 1 can now be made with confidence.     

Franck-condon factors for I2 lines arising from Ar, K and He-Ne laser excitation

We report Franck-Condon factors for the I₂ B → X transitions excited by several lines of Ar⁺, Kr⁺ and He-Ne lasers and observed in fluorescence. The most recent and accurate molecular constants of Luc have been used in the calculation.     

A novel procedure for the aromatization of ring a in 19-nortestosterone

A convenient, 40% overall yield synthesis of 2,3,17β-triacetoxy-1,3,5(10)-estratriene is described, which involves epoxidation of 19-nortestosterone and subsequent acetylation, lead tetra-acetate acetoxylation of the so-formed 17β-acetoxy-4β,5-epoxy-5β-estran-3-one, and aromatization of ring A, by means of acidic alumina, of the resulting 2α and 2β epimers of 2,17β-diacetoxy-4β,5-epoxy-5β-estran-3-one.     

Peptides—XXXXIII: Synthesis of the 94–104 fragment of a lysozyme analogue

The synthesis of the (94–104) fragment of a lysozyme analogue is reported by union of the protected (94–98) and (99–104) subfragments using the N-hydroxysuccinimide active ester of the (94–98) fragment. This choice of coupling method was made on the basis of a study employing a range of established methods using the criteria of yield and minimum racemisation.     

Reaction of organic sulfur compounds with superoxide anion—III : Oxidation of organic sulfur compounds to sulf1nic and sulfonic acids

Organic sulfur compounds such as disulfide, thiolsulfinate, thiolsulfonate, thiol, sodium thiolate, and sodium sultinale were readily oxidized to both sulfinic and sulfonic acids with superoxide anion generated from potassium superoxide and 18-crown-6-ether under mild conditions. However, both sulfide and sulfoxide did not react with superoxide anion, O₂^-. Although thiol was easily oxidized to disulfide with O₂^? at room temperature, it was oxidized further with O₂^? at 60° to the corresponding sulfinic and sulfonic acids. Symmetrical disulfide was obtained in the reaction of unsymmetrical thiolsulfinate or thiolsulfonate along with both sulfinic and sulfonic acids. Most reactive was thiolsulfinate which reacted at lower temperature ranging between ?40 and 0° to afford the products within 30 min. Relative reactivities fall in the following order: thiolsulfinate > thiolsulfonate > disulfide ? sodium thiolate ? sodium sulfinate. Polar solvents such as pyridine and acetonitrile were more effective than such a less polar solvent as benzene in the oxidation of the substrate, and increased amount of the crown ether shortened the reaction time. Nucleophilic attack of O₂^? and electron transfer processes are believed to be involved in these oxidations.     

Vicinal phenyl group shift in the lead tetraacetate and related oxidations of 5,5,5-triphenyl-1-pentanol

In the lead tetraacetate and heavy metal-bromine oxidations of 5,5,5-triphenyl-1-pentanol 1d, the major cyclization product obtained was the rearranged 2,2,3-triphenyltetrahydro-2H-pyran 11d, resulting from homolytic and heterolytic 1,2-phenyl group shift (the latter only in the lead tetraacetate reaction) in the respective intermediate species with electron deficient δ-carbon 4d and 6d.     

Automated nephelometric determination of polyvinyl-pyrrolidone in salazopyrin.

An automatic nephelometric method is described for the determination of polyvinyl-pyrrolidone (PVP) in Salazopyrin. PVP is separated from the other constituents of Salazopyrin on a two-layer anion and cation exchanger in 96—99 % yield. The PVP is determined nephelometrically after precipitation with perchloric acid, in an AutoAnalyzer II system at 30 samples per hour with a relative standard deviation of 0.5 %. The nephelometric response of the precipitation reaction is strongly dependent upon reaction time and, because of the precipitation reagent used, on the molecular weight of the sample. An investigation of the influence of these factors is presented.     

Peptides-XXXXV: Synthesis of the 118–129 fragment of a lysozyme analogue

The synthesis of the (118–129) fragment of a Lysozyme analogue was achieved by the fragment coupling approach. The fragments were assembled using the DCCI/HONSu method and the (118–122), (123–126) and (127–129) subfragments were each built up in a stepwise manner. At several stages the diphenylphosphinic mixed anhydride method was found to be superior to the pivalic mixed anhydride method.     

Structure-reactivity relationship in the solvolysis of 5,10-secosteroidal 5-p-nitrobenzoates1

The solvolysis of (Z)- and (E)-3β-acyloxy-5,10-seco-1(10)-cholesten-5β-ol p-nitrobenzoates 4 and 5 has been investigated and compared with the solvolytic reactivity of the epimeric (Z)- and (E)-5α-p-nitrobenzoates 1 and 2, as well as of the reference compound, i.e. the 1,10-saturated 5α-p-nitrobenzoate. Kinetic data and product analysis revealed that the relative spatial orientation of the 1(10)-olefinic double bond and the chiral center at C(5) in the 10-membered ring, which these secosteroidal 5-p-nitrobenzoates can adopt in the transition state, is the main factor which determines their solvolytic behaviour, so that the esters 1,2 and 5 solvolyse with transannular double bond participation, while such an interaction is not present in the case of the (Z)-5β-ester 4.     

Peptides—XXXXII: Synthesis of the 76–93 fragment of a lysozyme analogue

The synthesis of the (76–93) fragment of a lysozyme analogue was achieved using a fragment condensation approach employing the protected subfragments (76–79), (80–86), and (87–93). The utility of Bates' reagent in conjunction with N-hydroxysuccinimidc was examined for the linking of fragments. The resulting protected peptide (76–93) was found to be one of the most insoluble encountered in this whole programme directed towards the synthesis of a lysozyme analogue.     

Peptides-XXXXVI: Studies in the synthesis of an analogue of hen egg white lysozyme

The previously synthesised (1–37), (38–75), (76–93), (94–104), (105–117) and (118–129) fragments of the analogue were combined making extensive use of the DCCI/HONSu method. The final coupling involved the (1–75) and (76–129) sub-fragments. Aggregation of the latter fragment caused problems in purification by routine gel filtration methods employing Enzacryl K2 or Sephadex LH60. The fully protected (1–129) product was partially purified by washing, then deprotectcd and purified by gel filtration and ion exchange chromatography. Satisfactory removal of the acetamidomethyl group used for cysteine protection could not be achieved.     

Ground state geometry of cinso

The ground state geometry for ClNSO is investigated using ab initio calculations in a moderately large basis set. Variation of the dihedral angle yields a planar syn geometry. The geometry is discussed on the basis of a population analysis.     

Charge distributions in molecules and ions: mindo 3 calculations. an alternative of the charge localisation concept in mass spectrometry

The charge distributions in a series of molecules A and their ions A⁺ and A²⁺ and in a second series B and their ions BH⁺ and BH²⁺ are presented. It is shown that their distributions are consistent with the conventional concepts of electronegativity, but not with those of the intermediate ion structures in the charge localisation concept of fragmentation processes in mass spectrometry. The charge distributions show that the carbon adjacent to a heteroatom has a considerable positive charge which apparently makes its bond to the next carbon atom weak and prone to fission which is a dominant process in the fragmentation of the positive ion.     

The noncumulative effect of methyl substituents on the rate of addition of benzeneselenenyl chloride to olefins1

The rates and products of addition of benzeneselenenyl chloride to ethylene and its six Me substituted derivatives have been determined in methylene chloride at 25°. Unlike the addition of 4-chlorobenzenesulfenyl chloride to this same series of compounds, the effect of Me groups on the rates of addition is not cumulative. Also the regiochemistry of the product is different. For arenesulfenyl chloride additions, products of anti-Markownikoff orientation are formed preferentially under conditions of kinetic control. Under similar conditions regiospecific formation of the Markownikoff adduct is observed for the addition of benzeneselenenyl chloride to methylpropene and 2-methyl-2-butene. These data indicate a difference in both rate and product determining transition states between additions of arenesulfenyl and selenenyl chlorides to alkenes.