摘要:

2-Hydroxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline (1) reacts with acetylenic and olefinic unsaturated systems by addition of the 2-acetoxy-2-propyl group and a hydrogen atom, respectively, to the two atoms forming the multiple bond. The regiochemistry of addition to unsymmetric unsaturated systems is that predicted for a radical chain mechanism, in which the 2-acetoxy-2-propyl radical adds to the multiple bond so as to form the more stable free radical which then abstracts a hydrogen atom from the hydroxyl group of1. Polymerization of the unsaturated substrate, as well as abstraction of allylic hydrogen (if any) are competing processes. Yields of adducts, based on1, ranged from 80% in reaction with crotonaldehyde to 10% in reaction with cyclohexene.

ISSN:0008-4042    

DOI:10.1139/v76-190

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

tert-Butylazodiphenylcarbinol1decomposes in benzene solution by a chain mechanism involvingtert-butyl radicals. Many olefinic compounds and azobenzene act as radical traps and are hydro-tert-butylated by1. The regiochemistry of hydro-tert-butylation of unsymmetric alkenes is that expected for a mechanism which involves addition oftert-butyl radical so as to form the most stable radical adduct, which subsequently abstracts hydrogen from1.In some cases phenol acts as a catalyst for the hydroalkylation process. The novel catalytic effect of phenol in a radical chain process is attributed to the favourable thermochemistry for induced, concerted decomposition of1by radical attack at hydroxyl hydrogen.

ISSN:0008-4042    

DOI:10.1139/v76-191

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

tert-Butylazodiphenylcarbinol (Ph2C(OH)N=NCMe3,3) decomposes in oxygen-free benzene by the unimolecular radical mechanism characteristic of most azo compounds. In benzene or in carbon tetrachloride, with or without air present, decomposition of3is also induced by radicals through abstraction of hydroxyl hydrogen in concert with the formation of nitrogen. Radicals which induce decomposition of3include trichloromethyl,tert-butyl, phenylthiyl,tert-butylperoxy and possibly oxygen. The failure of inhibitors like thiophenol to stop chain decomposition of3is interpreted in terms of the thermochemistry of induced decomposition.

ISSN:0008-4042    

DOI:10.1139/v76-192

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A new metabolite has been isolated from cultures ofPithomyces maydicus. Evidence is presented that suggests its structure is cyclo(L-2-oxy-3-methylbutyryl-D-valyl-D-leucyl-L-2-oxy-4-methylvaleryl-L-2-oxy-3-methylbutyryl-L-N-methylleucyl),1.

ISSN:0008-4042    

DOI:10.1139/v76-193

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Further examination of the pithomycolide fraction of extracts of cultures ofPithomyceschartarumhas resulted in the isolation of a new depsipeptide, for which the structure cyclo(L-N-methylalanyl-L-valyl-D-3-oxy-3-phenylpropionyl-D-3-oxy-3-phenylpropionyl-L-2-oxy-3-methylbutyryl) is proposed.

ISSN:0008-4042    

DOI:10.1139/v76-194

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The crystal structure of β-D-acetyl cellobiose was studied by X-ray crystallography. The crystal data area = 31.814(4),b = 19.414(5),c = 5.614(1) Å, space groupP212121,Z = 4. The structure, solved by direct method, was refined by block-diagonal least-squares to a finalRvalue of 0.075 for 2605 observed reflections. The molecular conformation involves4C1pyranose rings with glycosidic torsion angles corresponding to near maximum extension of the molecule. Substantial differences in conformational angles were observed between this molecule and the unacetylated counterpart. The molecules lie along thea-axis of the unit cell.

ISSN:0008-4042    

DOI:10.1139/v76-195

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Intramolecular displacement by hydroxyl on the 1,2-epoxide group under basic or neutral conditions has been studied for seven of the stereoisomeric 1,2-diols derived by oxidation of the exocyclic double bond of1. In six of the examples (the seventh is ambiguous) the single or largely predominant product is that one of the less strainedcis-fused isomers which has the fewer unfavourable steric interactions leading to it, without regard to whether the displacement occurs at the secondary or tertiary epoxide carbon.

ISSN:0008-4042    

DOI:10.1139/v76-196

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

We have carried out calorimetric measurements leading to ΔHf0 = −60 kcal mol−1for Cr3+(aq). Further calorimetric measurements have led to enthalpies of reaction of Cr3+(aq) with HF(aq), Cl−(aq), Br−(aq), and SO42−(aq) to form the 'inner sphere' complexes CrF2+(aq), CrCl2+(aq), CrBr2+(aq), and CrSO4+(aq). Results of our measurements lead to ΔHf0 = (−60.0 ± 1.5) kcal mol−1for Cr3+(aq), ΔHf0 = −136.8 kcal mol−1for CrF2+(aq), ΔHf0 = −93.7 kcal mol−1for CrCl2+(aq), ΔHf0 = −80.1 kcal mol−1for CrBr2+(aq), and ΔHf0 = −269.7 kcal mol−1for CrSO4+(aq).

ISSN:0008-4042    

DOI:10.1139/v76-197

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

McDonald's study of the absorption band at 3749 cm−1, due to the O—H stretching vibration of hydroxyl groups on outgassed powdered silica, revealed substantial changes in center frequency and band area upon adsorption of Ar. The main features of these changes are accounted for here using an optical model for porous adsorbent–adsorbate systems due to Dignam, Rao, and Roth. The possibility of using the measured change in band intensity on adsorbing an inert gas, as a general indicator of the orientational distribution of the adsorbed species responsible for the band, is noted.

ISSN:0008-4042    

DOI:10.1139/v76-198

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The thermal lability of 2-(2′ 4′-dinitrophenylamino)-2-deoxy-D-glucose (DNP-glucosamine) in alkaline borate buffer is reported. This was dependent on borate ion concentration at constant pH. Of the many reaction products, 2,4-dinitroaniline was isolated and identified by spectroscopic and other means. It was formed in 20% yield. A mechanism of reaction is suggested.

ISSN:0008-4042    

DOI:10.1139/v76-199

出版商:NRC Research Press    

年代:1976

数据来源: NRC