1:1 Complexes of a range of Lewis acids with crotonaldehyde (1) have been systematically investigated by 1H and 13C nmr spectroscopy. Lewis acids employed were: BF3, BCl3, BBr3, SnCl4, TiCl4, SbCl5, AlCl3, EtAlCl2, Et2AlCl, Et3Al2Cl3, and Et3Al. Chemical shift changes in 1H nuclei remote from the Lewis acid group were found to be remarkably regular and consistent. The study has been extended to tiglaldehyde (2), pent-3-en-2-one (3), cyclohexenone (4), methyl crotonate (5), and crotonitrile (6) and the relationships between the chemical shift differences associated with complexation of these have been explored.

. Can. J. Chem. 60,809 (1982). Enthalpies of complexation of the a,P-unsaturated Lewis bases crotonaldehyde, 1; methyl crotonate, 2; mesityl oxide, 3; and crotononitrile, 4; with each of the Lewis acids SnCl,, TiCl,, SbCl,, and BC1, were measured in solution in CW,Cl,. The results indicate that while a qualitative agreement exists in the ranking of Lewis acids for each of the Lewis bases, there is only a modest quantitative correlation. Similarly, when compared with an nmr-derived Lewis acid scale, the enthalpies were found to agree with the qualitative ranking of Lewis acids, but exhibited only a poor correlation. RONALD F. CHILDS, D. LINDSAY MULHOLLAND et ALAN NIXON. Can. J. Chem. 60,809 (1982). On a mesure, en solution dans le CH,Cl,, les enthalpies de complexation des bases de Lewis a,P-non saturees, crotonaldehyde (I), crotonate de mtthyle (2), oxyde de mesityle (3) et crotononitrile (4) avec chacun des acides Lewis suivants: SnCl,, TiCl,, SbC1, et BC1,. Les resultats indiquent que des accords qualitatifs permettent d'ordonner chaque acide de Lewis pour chacune des bases de Lewis; toutefois la correlation quantitative n'est que modeste. De la mCme maniere, si on compare les enthalpies avec une tchelle d'acide de Lewis derivee de la rmn, on peut qualitativement ordonner les acides de Lewis mais la correlation est faible.[Traduit par le journal]Lewis acids are used to catalyse a variety of synthetically useful reactions of a,P-unsaturated carbonyl and nitrile compounds. In a previous paper we have reported a systematic examination of the nmr spectra of the complexes formed between some of these unsaturated bases and Lewis acids and have proposed an acid scale which, it was suggested, reflected the amount of charge induced at C3 of the base on complexation (1).There has been much discussion about and many attempts at correlating Lewis acid1Lewi.s base interactions (2). These include, among others, the hardlsoft concepts introduced by Pearson (3), the donorlacceptor numbers of Cutmann (4), Drago's E/C equation (3, and theoretical treatments of Mulliken and Pearson (6) and Klopman (7). The equilibrium constant or the heat of reaction is generally used to measure the strength of a Lewis acidlbase reaction.In our attempts to quantify the catalytic effects of Lewis acids on the reactions of unsaturated carbonyls and nitriles, it seemed of interest to compare the nmr-based scale mentioned above with the strength of the acidlbase interaction. As complex formation was essentially complete for nearly all the systems we had studied it seemed appropriate to base such a comparison on the heats of reaction. There have been some ,previous reports of the measurement of the BIi for reaction of unsaturated bases with Lewis acids (8) but insufficient for a meaningful comparison with our nmr-based scale.'Author to whom correspondence may be addressed.We report here a range of calorimetric measurements of these systems and examine the correlations with the nmr scale. Results and discussion Calorimetric meas~rrementsIdeally the en...

No abstract

ABSTRA ABSTRA ABSTRA ABSTRA ABSTRACT CT CT CT CT: A : A : A : A : Apple and or pple and or pple and or pple and or pple and orange juices packed in poly ange juices packed in poly ange juices packed in poly ange juices packed in poly ange juices packed in polyester bottles w ester bottles w ester bottles w ester bottles w ester bottles wer er er er ere stor e stor e stor e stor e stored in dar ed in dar ed in dar ed in dar ed in dark, intense fluor k, intense fluor k, intense fluor k, intense fluor k, intense fluorescent (1500 lux), escent (1500 lux), escent (1500 lux), escent (1500 lux), escent (1500 lux), and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic acid content and color changes acid content and color changes acid content and color changes acid content and color changes acid content and color changes. P . P . P . P . Poly oly oly oly olyester bev ester bev ester bev ester bev ester bever er er er erage bottles w age bottles w age bottles w age bottles w age bottles wer er er er ere made of poly e made of poly e made of poly e made of poly e made of polyethylene ter ethylene ter ethylene ter ethylene ter ethylene terephthalate (P ephthalate (P ephthalate (P ephthalate (P ephthalate (PET ET ET ET ET), or P ), or P ), or P ), or P ), or PET ET ET ET ET blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for P P P P PET to 373 nm for the 4% P ET to 373 nm for the 4% P ET to 373 nm for the 4% P ET to 373 nm for the 4% P ET to 373 nm for the 4% PEN/P EN/P EN/P EN/P EN/PET blend. S ET blend. S ET blend. S ET blend. S ET blend. Spectr pectr pectr pectr pectral irr al irr al irr al irr al irradiance adiance adiance adiance adiance, visible light intensity , visible light intensity , visible light intensity , visible light intensity , visible light intensity, and light distr , and light distr , and light distr , and light distr , and light distribution w ibution w ibution w ibution w ibution wer er er er ere e e e e evaluated in the light chambers and compared with supermarket display lighting and outdoor daylight conditions. evaluated in the light c...

2,3-Diaminobutanoic acid (DAB) is found in several peptide antibiotics, toxins, and biologically active molecules. This paper describes the practical and highly enantioselective synthesis of all four N,N'-protected DAB stereoisomers using an asymmetric Rh(I)-phosphine-catalyzed hydrogenation of isomeric enamides as the key step. Thermal and photochemical isomerization of the enamide hydrogenation substrates coupled with catalyst-geometric isomer pairing allows targeted synthesis of single DAB isomers in maximum yield.