pKa values of protonated α,β-unsaturated cyclic carboxylic acids. Effect of ring size on acidities

1978 ◽  
Vol 56 (15) ◽  
pp. 2003-2007 ◽  
Author(s):  
S. N. Bhat ◽  
Rama Rao ◽  
K. Ranganayakulu
Keyword(s):  
Double Bond ◽  
Carboxylic Acids ◽  
Acid Strength ◽  
Ring System ◽  
Ring Size ◽  
Methyl Group ◽  
Tiglic Acid ◽  
Conjugate Acid ◽  
The Difference ◽  
Steric Inhibition Of Resonance

The pKa values of protonated α,β-unsaturated acids, namely tiglic, cyclopentene carboxylic, cyclohexene carboxylic, and cycloheptene carboxylic acids have been determined spectrophotometrically and the values are −4.08, −4.05, −3.88, and −3.84, respectively. The conjugate acid of tiglic acid is a stronger acid than that of crotonic acid (pKa − 3.94) and the difference in acid strength is explained on the basis of steric inhibition of resonance by the α-methyl group. All the protonated cyclic acids are shown to be somewhat weaker than the corresponding acyclic ones. Several factors have been considered to explain the acid strength of these cyclic α,β-unsaturated acids. It has been shown that the ease of placing the double bond exo to the ring system is responsible for the changes in acidity of the above cyclic systems.

BEZIEHUNGEN ZWISCHEN SUBSTITUTION IM RING A UND ABBAU IM STOFFWECHSEL BEI VERWANDTEN DES TESTOSTERONS

1962 ◽  
Vol 41 (4) ◽  
pp. 494-506 ◽  
Author(s):  
H. Langecker
Keyword(s):  
Double Bond ◽  
Ring System ◽  
Keto Group ◽  
Hydroxyl Group ◽  
Methyl Group ◽  
Structural Peculiarities ◽  
Metabolic Degradation ◽  
The Difference ◽  
Testosterone Metabolites ◽  
Derivatives Of

ABSTRACT Judging from the metabolites found in the urine, 1-methyl-androst-1-en-17β-ol-3-one (methenolone) and testosterone are metabolized in a different manner. For further clarification, other derivatives of testosterone with modifications in Ring A were investigated with regard to the oxidation of the 17-hydroxyl group. The production of urinary 17-ketosteroids decreased in the following sequence: testosterone; 1α-methyltestosterone and androstan-17β-ol-3-one; 1β-methyl-androstan-17β-ol-3-one; 2α-methyl-androstan-17β-ol-3-one and androst-1-en-17β-ol-3-one; 1α-methyl-androstan-17β-ol-3-one; 1-methyl-androsta-1,4-dien-17β-ol-3-one; 1,17α-dimethyl-androst-1-en-17β-ol-3-one and 1 -methyl-androst-1 -en-17β-ol-3-one (methenolone). The difference in metabolic degradation is also demonstrated in the fractionation of the urinary ketones. While after the administration of testosterone practically only hydrogenated 17-ketones are observed in the urine, the unchanged compound is still traceable in remarkable quantities after the administration of methenolone, along with minor quantities of the corresponding diketone. Testosterone-metabolites here are absent, whereas they represent the major substances present after the administration of androst-1-en-17β-ol-3-on. Following the administration of 1α-methyltestosterone only hydrogenated 17-ketones are detected which are still partly methylated. The 1-methyl-group and the Δ 1-double-bond seem to be responsible for the inhibition of the oxidation of methenolone in the 17-position. In addition, the hydrogenation of the double-bond and the reduction of the 3-keto-group are inhibited, obviously on account of the same structural peculiarities. The demethylation of methenolone is also inhibited. Any change in the steroid ring system forms a new substrate, thus producing new conditions for the enzymatic attack in the metabolic degradation.

scholarly journals Stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene: a general intramolecular Diels–Alder approach to tricyclic sesquiterpenes

1985 ◽  
Vol 63 (4) ◽  
pp. 993-995 ◽  
Author(s):  
Kazimierz Antczak ◽  
John F. Kingston ◽  
Alex G. Fallis
Keyword(s):  
Double Bond ◽  
Methyl Ester ◽  
Total Synthesis ◽  
Ring System ◽  
Diels Alder ◽  
Exocyclic Double Bond ◽  
Total Syntheses ◽  
Methyl Group ◽  
Secondary Hydroxyl ◽  
Selective Hydrogenolysis

Stereoselective total synthesis of (±)-sinularene and (±)-5-epi-sinularene are described. The sequence employs a "blocked" cyclopentadiene in which the cyclopropane unit also serves as a latent methyl group. Thus intramolecular [4 + 2] cycloaddition of the substituted methyl spiro[2.4]hepta-4,6-dien-1-yl)-2-pentenoate 11 affords 5-benzyloxy-6-isopropyl-8-carbomethoxytetracyclo[5.4.01,7.02,4.02,9]undec-10-ene (12) which after selective hydrogenolysis generates the tricyclo[4.4.01,6.02,8]decane (sinularene) ring system. Removal of the secondary hydroxyl function (Ph3P/CCl4/CH3CN; H2/Pd/C), reduction of the methyl ester (LiAlH4), and introduction of the exocyclic double bond (acetate pyrolysis, 550 °C) completes the synthesis of (±)-sinularene in 14 steps from cyclopentadiene. A parallel series of reactions employing the isopropyl epimer of 12 affords (±)-5-epi-sinularene.

A general intramolecular Diels–Alder approach to tricyclic sesquiterpenes: stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene

1987 ◽  
Vol 65 (1) ◽  
pp. 114-123 ◽  
Author(s):  
Kazimierz Antczak ◽  
John F. Kingston ◽  
Alex G. Fallis ◽  
Alfred W. Hanson
Keyword(s):  
Double Bond ◽  
Methyl Ester ◽  
Ring System ◽  
Diels Alder ◽  
Exocyclic Double Bond ◽  
Total Syntheses ◽  
Methyl Group ◽  
X Ray ◽  
12 Steps ◽  
Selective Hydrogenolysis

Stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene are described. The sequence employs a "blocked" cyclopentadiene in which the cyclopropane unit also serves as a latent methyl group. Thus intramolecular [4 + 2] cycloaddition of the substituted methyl spiro[2.4]hepta-4,6-dien-1-yl-2-pentenoate 13c affords 5-benzyloxy-6-isopropyl-8-carbomethoxytetracyclo[5.4.01,7.02,4.02,9]undec-10-ene (14c), which after selective hydrogenolysis generates the tricyclo[4.4.01,6.02,8]decane (sinularene) ring system. Removal of the secondary hydroxyl function by elimination and hydrogenation (Ph3P/CCl4/CH3CN; H2/Pd/C), reduction of the methyl ester (LiAlH4), and introduction of the exocyclic double bond (acetate pyrolysis, 550 °C) completes the synthesis of (±)-sinularene in 12 steps from aldehyde 7. A parallel series of reactions employing the isopropyl triene epimer 13a affords (±)-5-epi-sinularene. X-ray analyses of the triene 13a and the adduct 14a are also reported.

Some Analogs of 4-(2',4'-Difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic Acid: Synthesis and Antiinflammatory Activity

1995 ◽  
Vol 60 (6) ◽  
pp. 1026-1033 ◽  
Author(s):  
Miroslav Kuchař ◽  
Václav Vosátka ◽  
Marie Poppová ◽  
Eva Knězová ◽  
Vladimíra Panajotovová ◽  
...  
Keyword(s):  
Double Bond ◽  
Antiinflammatory Activity ◽  
Acid Synthesis ◽  
Reaction Conditions ◽  
Methyl Group ◽  
Oxobutanoic Acid

Analogs of 4-(2',4'-difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic acid (I, flobufen), containing a double bond (II, IV, V, VII, VIII) or a methyl group in position 3 (VI) were prepared. Their antiinflammatory activity was evaluated and compared with that of flobufen. None of the mentioned analogs reached the activity of the standard. Isomerization of the unsaturated derivatives is connected with a shift of the double bond, Z-E transformation or lactonization. Reaction conditions and spectra of the compounds prepared are described.

Direct N-acylation of sulfoximines with carboxylic acids catalyzed by the B3NO2 heterocycle

2017 ◽  
Vol 53 (54) ◽  
pp. 7447-7450 ◽  
Author(s):  
Hidetoshi Noda ◽  
Yasuko Asada ◽  
Masakatsu Shibasaki ◽  
Naoya Kumagai
Keyword(s):  
Carboxylic Acids ◽  
Ring System ◽  
System P

Dehydrative coupling of sulfoximines and carboxylic acids is rendered catalytic by a heterocyclic catalyst featuring the B3NO2 ring system.

Oxidative decarboxylation of the 3-methyl-2-carboxynorbornanes with lead tetraacetate

1976 ◽  
Vol 54 (8) ◽  
pp. 1222-1225 ◽  
Author(s):  
J. B. Stothers ◽  
K. C. Teo
Keyword(s):  
Carboxylic Acids ◽  
Lead Tetraacetate ◽  
Starting Material ◽  
Oxidative Decarboxylation ◽  
Methyl Group

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4 decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNi substitution.

The Dinitration of Dimethylacetanilides

2003 ◽  
Vol 2003 (5) ◽  
pp. 303-304 ◽  
Author(s):  
Inmaculada C. Rodriguez Medina ◽  
James R. Hanson
Keyword(s):  
Methyl Group ◽  
H Nmr ◽  
Nmr Methods ◽  
Steric Inhibition Of Resonance

The orientation of dinitration of the dimethylacetanilides has been examined by 1H NMR methods and a possible enhancement of the hyperconjugative influence of a methyl group has been considered as an additional factor augmenting the effect of the steric inhibition of resonance on the orientation of substitution.

Structural Homogeneity in Unsaturated Fatty Acids of Marine Lipids. A Review

1964 ◽  
Vol 21 (2) ◽  
pp. 247-254 ◽  
Author(s):  
R. G. Ackman
Keyword(s):  
Fatty Acids ◽  
Double Bond ◽  
Polyunsaturated Fatty Acids ◽  
Chain Length ◽  
Unsaturated Fatty Acids ◽  
Analytical Data ◽  
Double Bonds ◽  
Marine Origin ◽  
Methyl Group ◽  
Marine Lipids

Consideration of recent analytical data supports the conclusion that the longer-chain polyunsaturated fatty acids of marine origin are all structurally homogeneous in that the double bonds are cis, the double bonds methylene interrupted, and that, with the exception of the C16 chain length, the ultimate double bond will normally be three, six or nine carbon atoms removed from the terminal methyl group.

The Structure of Polyisoprenes. II. The Structure of β-Gutta-Percha

1945 ◽  
Vol 18 (2) ◽  
pp. 280-283
Author(s):  
G. A. Jeffrey
Keyword(s):  
Molecular Structure ◽  
Double Bond ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
Methyl Group ◽  
X Ray ◽  
Gutta Percha ◽  
Qualitative Estimate

Abstract The x-ray diffraction data at present available from β-gutta-percha are shown to be insufficient to distinguish fine details of molecular structure. Since a qualitative estimate of the intensities on the fibre diagram can be adequately satisfied by a model having normal interatomic distances and valency angles, no evidence exists for the improbable distortion of the methyl group out of the plane of the double bond previously ascribed to the molecule.

scholarly journals Unusual Regularity in GC Retention of Simple Amino Acid Derivatives

2019 ◽  
Vol 6 (1) ◽  
pp. 3-14 ◽  
Author(s):  
Igor G. Zenkevich ◽  
Nino G. Todua ◽  
Anzor I. Mikaia
Keyword(s):  
Gas Chromatography ◽  
Retention Index ◽  
Methyl Esters ◽  
Elution Order ◽  
Alkyl Esters ◽  
Methyl Group ◽  
The Difference ◽  
Direct Use ◽  
Derivatives Of

Background: Application of simple regularities and general principles along with direct use of reference gas chromatography retention index data for reliable structure determination of compounds can be enhanced by determination of new regularities that are specific to certain structural elements. Objective: Revelation and interpretation of an anomaly in the elution order of alkyl esters of alkoxycarbonyl derivatives of glycine and alanine on standard and semi-standard non-polar phases. Method: Preliminary derivatization of amino acids to alkyl esters of N-alkoxycarbonyl analogs and interpretation of their gas chromatographic characteristics. Results: Alkyl esters of N-alkoxycarbonyl derivatives of alanine (Alkyl = C2H5, n- and iso-C3H7) elute prior to the same derivatives of glycine, despite the presence of an additional methyl group at C(2) in the molecule. Elution order is reversed for methyl esters of N-methoxycarbonyl derivatives. Conclusion: It is established that the peculiar behavior of alkyl esters of N-alkoxycarbonyl derivatives of glycine and alanine agrees with the concepts of gas chromatography and the known retention index regularities of organic compounds. A decrease of retention index values is a result of an introduction of an additional methyl group to a carbon atom connected to two polar fragments in a molecule like CH2XY. The dependence of the difference of retention index values for homologs of the types of CH3-CHXY and CH2XY vs. the total mass of fragments (X + Y) is similar to those for other sub-groups of analytes.

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