Showing papers on "Substituent published in 1972"
171 citations
158 citations
TL;DR: In this article, the carboxy-group of a series of substituted N-methylmaleamic acids is shown to be remarkably sensitive to the pattern of substitution on the carbon-carbon double bond.
Abstract: The efficiency of intramolecular catalysis of amide hydrolysis by the carboxy-group of a series of substituted N-methylmaleamic acids is remarkably sensitive to the pattern of substitution on the carbon–carbon double bond. A single alkyl group increases the rate of hydrolysis by a factor which increases with its size. A second alkyl substituent has a disproportionately larger effect, which is sharply reduced when the two groups are joined together in a ring. The rates of hydrolysis of a series of dialkyl-N-methylmaleamic acids range over more than ten powers of ten, and the ‘effective concentration’ of the carboxy-group of the most reactive compound studied is greater than 1010M. This amide, dimethyl-N-n-propylmaleamic acid, is converted into the more stable dimethylmaleic anhydride with a half-life of less than 1s at 39 °C below pH 3. The mechanism of catalysis, and the factors responsible for this extremely high reactivity, are discussed.
154 citations
TL;DR: In this article, the authors discuss the cyclizations of ortho-substituted t-anilines with an ortho substituent and the t-nitrogen and show that these cyclizations can be rationalized by an imine bearing a good leaving group.
Abstract: Publisher Summary It is the purpose of this chapter to collate all the available material relating to the “t-amino effect” and to attempt a rationalization of its operative influence in a mechanistic manner. The cyclizations of ortho-substituted t-anilines are described in two main sections. The first discusses ring closures between the ortho substituent and the t-nitrogen. Varieties of seemingly unrelated reactions have been reported in which a t-aniline with an ortho substituent of the type N-C-Y is converted into a benzimidazole with loss of a group from the t-nitrogen. All these cyclizations can be rationalized by the intermediacy of an imine bearing a good leaving group. While the second deals with those ring formations which involve the a-methylene groups attached to the nitrogen. The reactions which fall into this category conform to a basic mechanism for an unsaturated ortho substituent (A=B) capable of mesomerism. The polarized mesomer is set up for further reaction since the hydrogens of the a-methylene group are rendered labile by the charged nitrogen, and are consequently abstracted by the nucleophilic center (B-). Here, the discussion will be divided into sections according to the functiona1 group (o-nitroso and o-nitro groups, o-amino and o-acylamino groups, o-azo group, o-azomethine group (=n=c), and o-carbonyl (c=o) and o-imine (c=n) groups) situated at the ortho position.
129 citations
123 citations
TL;DR: A series of p -substituted phenyldimesitylboranes has been synthesized by reaction of dimesity lboron fluoride with appropriately substituted phenyllithium derivatives.
100 citations
TL;DR: The results obtained in the investigation of the dissociation constants of carboxylic acids of known geometry and free from the complicating features of pi electron interactions and steric effects have established that the magnitude of the polar effect does not depend on either the number or the nature of the atoms between the substituent and the reaction site as discussed by the authors.
Abstract: The results obtained in the investigation of the dissociation constants of carboxylic acids of known geometry and free from the complicating features of pi electron interactions and steric effects have established that the magnitude of the polar effect does not depend on either the number or the nature of the atoms between the substituent and the reaction site, nor do such substituent contributions depend on the number of paths available for their propagation.
96 citations
TL;DR: These findings delineate completely the effect on the cytokinin activity of zeatin of variation in side chain geometry, presence and position of the methyl substituent, absence and geometry of hydroxyl substitution, presence of the double bond, and of side chain cyclization.
Abstract: Geometric and position isomers of zeatin and of ribosylzeatin and other compounds closely related to zeatin have been tested in the tobacco (Nicotiana tabacum var. Wisconsin No. 38) bioassay. None was more active than zeatin itself. There was a much greater difference in activity (> 50-fold) between trans- and cis-zeatin than between trans-isozeatin [6-(4-hydroxy-2-methyl-trans-2-butenylamino) purine] and cis-isozeatin [6-(4-hydroxy-2-methyl-cis-2-butenylamino) purine], the latter being less active than cis-zeatin and trans-isozeatin. Higher concentrations were required for equivalent callus growth stimulated by the 9-ribosyl derivatives, which followed an order of decreasing activity: ribosyl-trans-zeatin > ribosyl-cis-zeatin > ribosyl-trans-isozeatin > ribosyl-cis-isozeatin, corresponding roughly to that of the bases. The effect of side chain, double bond saturation was to diminish the activity, and in the dihydro series the shift of the methyl group from the 3- to the 2-position in going from dihydrozeatin to dihydroisozeatin [6-(4-hydroxy-2-methylbutylamino) purine] resulted in a 70-fold decrease in activity. cis-Norzeatin [6-(4-hydroxy-cis-2-butenylamino) purine], which was less than one-fifth as active as cis-zeatin, showed the effect of complete removal of the side chain methyl group, and cyclic-norzeatin [6-(3,6-dihydro-1,2-oxazin-2-yl) purine] was about 1/100 as active as cis-norzeatin. These findings delineate completely the effect on the cytokinin activity of zeatin of variation in side chain geometry, presence and position of the methyl substituent, presence and geometry of hydroxyl substitution, presence of the double bond, and of side chain cyclization.
90 citations
87 citations
87 citations
TL;DR: In this paper, the rates of alkaline hydrolyses of 24 m- and p-substituted benzyl benzoates were measured in 70% (v/v) aqueous acetone at 25°C.
Abstract: The rates of the alkaline hydrolyses of 24 m- and p-substituted-benzyl benzoates were measured in 70% (v/v) aqueous acetone at 25°C. The given set of σ0 constants was precisely identical with our standard set derived from m- and p-substituted ethyl phenylacetates. The general utility of σ0 constants is demonstrated for unexalted and exalted resonance reactivities as the reference scale in our LArSR equation:logk⁄k0=ρ(σ0+r+Δ\barσ\overset+R+r−Δ\barσ\overset−R)
TL;DR: In this paper, Steviol (I) and erythroxydiol A (II), tetracyclic diterpenes with a substituent at the bridgehead C-13 position, were synthesized by using two interesting rearrangement reactions.
TL;DR: In this paper, the relative rates of the homolytic alkylation of protonated 4-substituted pyridines with methyl, n-propyl and n-butyl radicals, obtained by the silver-catalyzed decarboxylation of acids with ammonium peroxydisulphate, are reported.
TL;DR: In this article, the photoelectron spectra of substituted ethylenes, H 2 C=CHX (X = H, CH 3, SiH 3, CH 2 CH 3, CH 2 SiH3 ) are discussed in the light of the results of CNDO-type molecular orbital calculations.
TL;DR: The reaction of several variously substituted pyridines with bis(acetylacetonato)oxovanadium(IV), VO(ACA)2, has been studied as mentioned in this paper.
TL;DR: In this article, the synthesis of 1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid derivatives is described, most of which have either an alkoxy or a basic substituent in position 4.
TL;DR: In this article, the path of reaction is determined by the character of substituent R4 in 10, where the starting materials are discussed and the scope and limitations of these reactions and accessibility of starting materials is discussed.
Abstract: Mono- and bis-(2-hydroxyphenyl)-s-triazines 4, 14, 18, 22, 28, 29 can be prepared by (a) reaction of salicylic acid esters 2 with amidines 3; (b) reaction of 4H-1, 3-benzoxazin-4-ones 10 with amidines 3; and (c) Friedel-Crafts-reaction of chloro-s-triazines 26, 27 with resorcinol 24.
In case (b) the path of reaction is determined by the character of substituent R4 in 10. Scope and limitations of these reactions and accessibility of starting materials are discussed.
TL;DR: It appears that the conformations taken by dipeptidic molecules when dissolved, at a very low concentration, are mainly determined by specific intramolecular forces.
Abstract: Several experimental methods have been used for studying the conformations taken by dipeptidic molecules when dissolved, at a very low concentration. in an inactive solvent such as carbon tetrachloride. Through systematic investigations performed by infrared and nmr spectroscopy. it has been possible to obtain accurate data about these conformations and to compare with the results of various theoretical treatments. Several typical examples are reported which concern aminoacid derivatives containing a paraffinic. an aromatic or a polar side substituent. It appears that the conformations taken by such molecules are mainly determined by specific intramolecular forces. These results agree only with the conclusions of the theoretical calculations in which such interactions have been considered.
TL;DR: In this paper, Substituent effects on the geometry of some trigonal radicals have been studied in the context of molecular physics, and the authors have shown that substitutent effects have a strong influence on the geometrical properties of some radicals.
Abstract: (1972). Substituent effects on the geometry of some trigonal radicals. Molecular Physics: Vol. 23, No. 1, pp. 209-212.
TL;DR: The results of this study show that data from different laboratories using different types of compounds can be quantitatively compared and from such comparisons a self-consistent picture emerges.
TL;DR: The results indicate that the γ elimination step catalyzed by cystathionine synthase is unconcerted and that the enzyme is efficiently designed for general base attack on an amino acid β hydrogen.
TL;DR: In this article, NMR chemical shifts of the hydroxyl proton of m-and p-substituted phenols were determined in aprotic DMF and DMSO solutions.
Abstract: NMR chemical shifts of the hydroxyl proton of m- and p-substituted phenols were determined in aprotic DMF and DMSO solutions The effect of substituents on the hydroxy chemical shift was correlated much more excellently with our LArSR relationship, Δδ=ρ(σ0+rΔ\barσ\barR), than with simple Hammett equation, ρσ0 or ρσ− The correlation resulted in ρ=1655 and r=0639 in DMF with correlation coefficient 09992 and ρ=1530 and r=0673 in DMSO with a correlation coefficient 09990 Anisotropy effect of any substituent was not significant The deviations of particular substituents were ascribed to the modification of the electronic characters of substituents due to strong substituent-solvent interactions in DMF (or DMSO) The inductive and resonance substituent constants, (σi)DMF and (Δ\barσ\barR)DMF, were determined, on the basis of the assumption that the solvent-modification of a given substituent is practically the same at both meta and para positions
TL;DR: In this paper, a recent report (J. Organometal. Chem., 36 (1972)227) that fluorophenyl(trifluoromethyl)mercury compounds can be prepared by decarboxylation of the respective fluoropolymercuric trifluoroacetates in 1,2-dimethoxyethane at 60-70° is shown to be incorrect by comparison of the claimed products with authentic m- and p-FC6H4HgCF3 and FC6HgO2CCF3.
TL;DR: In this paper, the 1 H NMR spectra of a series of homoannularly bridged ferrocenophane derivatives have been recorded and it has been shown that the region close to the iron atom is strongly shielding in nature.