bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal substitution reactions of cupric benzoate IV
Authors: Schoo W. , Veenland J. U. , van Velzen J. C. , de Boer Th. J. , Sixma F. L. J. 
Published: September 2010

AbstractThe reaction of cupric benzoate with carbon tetrachloride leads to the formation of a mixture of benzoyl chloride and ortho‐chlorobenzoyl chloride. On the basis of these data, the reactions of cupric benzoate are reconsidered. Most probably at about 200° the cupric benzoate forms a radical, stabilised by interaction of the cupric‐ion with the ortho position. With this stabilised radical all the reactions described in this and previous1,2,3 papers can be explained.
Efficiency of chromatographic procedures: II. Optimum conditions for the separation of the antipodes of DL‐kynurenin by paper adsorption chromatography
Authors: de Ligny C. L. , Schmidt H. M. , de Vries W. 
Published: September 2010

AbstractThe influence of the kind of paper and the temperature on the separation of the antipodes of DL‐kynurenin has been investigated.
Thermodynamic properties of transition metal compounds and coordination complexes III. Heats of formation of some complexes of the divalent metals Mn ‐ Zn
Authors: Schuit G. C. A. 
Published: September 2010

AbstractThe heats of formation of octahedrally coordinated complexes of O‐containing ligands follow a relationship, proposed earlier

while those of N‐containing ligands follow a more involved equation

where I‐the ionization potential (I1 + I2 of the atom, CL, ΔL and γL are constants dependent on the ligand, while nt and ne are the number of 3d‐electrons in the t2g and the eg‐antibonding orbitals. For O‐ligands, as for those ligands discussed previously ΔL ∼ Δs (spectroscopic ligand field splitting factor), while for N‐ligands, (ΔL + γL) ∼ Δs. It is proposed that γL represents the depression in energy of the t2g‐levels by acceptor π‐bonding connected with a 3p‐orbital of atomic N: it is numerically equal to 6 kcal/at for a central ion with an environment of 6 N‐atoms.The ΔL and CL‐values for O‐ and N‐containing ligands appear almost equal, suggesting the σ‐bonds to be almost equal in strength.
Synthesis of a completely protected pentapeptide found in bacterial cell walls
Authors: Tesser G. I. , Nivard R. J. F. 
Published: September 2010

AbstractA synthesis is described of a protected pentapeptide, in which the amino‐acid sequence L‐alanyl‐D‐glutamyl‐L‐lysyl‐D‐alanyl‐D‐alanine, found in bacterial cell wall substances, is present. By the nature of its amino‐ and carboxyl‐protecting groups it seems suitable for condensation with N‐acetylmuramic acid, which is intended.
Synthesis of mixed‐acid phosphatidylserine containing unsaturated fatty acids
Authors: de Haas G. H. , van Zutphen H. , Bonsen P. P. M. , van Deenen L. L. M. 
Published: September 2010

AbstractThe synthesis is described of a mixed‐acid phosphatidylserine, containing one saturated and one unsaturated fatty acid, by a reaction between γ,β‐diacylglycerol‐L‐α‐iodohydrin and silver N‐t. butoxycarbonyl‐O‐(O‐benzylphospho)‐DL‐serine t. butyl ester.Some physical and biochemical properties of the unsaturated phosphatidylserine, viz. (γ‐oleoyl‐β‐palmitoyl)‐L‐α‐phosphatidyl‐DL‐serine, are given.
Chemistry of acetylenic ethers 70: Preparation of 1‐alkynyl thioethers and 1‐alkynyl selenoethers from sodium alkynylides, sulphur or selenium and alkyl halides
Authors: Brandsma L. , Wijers H. E. , Jonker C. 
Published: September 2010

AbstractA number of 1‐alkynyl thioethers and selenoethers RCC‐XR′ (XS or Se) have been prepared by reaction of sodium alkynylides, dissolved in liquid ammonia, with sulphur or selenium, followed by alkylation. 1,3‐Enynyl thioethers, RCHCH‐C≡C‐SR′, ω,ω‐diynyl thioethers R′S‐C≡C‐(CH2)n‐C≡C‐SR′ and 1,3‐diynyl thioethers RC≡C‐C≡C‐SR′ also can be obtained in this manner. The yields are satisfactory, except in the case of the ethynyl thioethers HC≡C‐SR′. Alkylselenoacetylenes HC≡C‐Se R′ are not accessible by this method.
On the impedance of galvanic cells: IX. The double layer capacity of the mercury‐1 M HCIO4 solution interface at high d.c. potentials
Authors: Sluyters‐Rehbach M. , Sluyters J. H. 
Published: September 2010

AbstractThe values of the double layer capacity of the mercury‐1 M HCIO4 solution interface at potentials where the dissolution of Hg contributes to the cell impedance, have been determined by the method previously described in parts VI1 and VII2.
Paper chromatography of diastereoisomeric tetrapeptide derivatives: Short communication
Authors: Kienhuis H. , Verweij A. 
Published: September 2010

AbstractIn six solvents the L‐D diastereoisomers of H‐gly‐asp‐ser‐gly‐OEt, H‐gly‐glu‐ser‐gly‐OEt, H‐gly‐asp‐ser(Ac)‐gly‐NH2 and H‐gly‐glu‐ser(Ac)‐gly‐NH2 have higher Rt values than the corresponding L‐L diastereoisomers.
Chemical determination of the cation valencies in cubic MntFe3‐tO4
Authors: Driessens F. C. M. 
Published: September 2010

AbstractAn analytical method is given for determining the distribution of cation valencies in MntFe3‐tO4 for o < t < 1.5 at 240°, based on the assumption that the existence of only Fe2+, Fe3+, Mn2+ and Mn3+ is possible and that no change in the equilibrium of the valencies occurs during rapid dissolution. The results are given for t = 0.50, 0.75, 1.00, 1.25 and 1.50. It is shown that near t = 1 the cations Mn3+ and Fe2+ are present simultaneously: The formula of manganese ferrite is found to be

with a possible error of ± 0.025 in the cationic ratio numbers.In addition the temperature dependence of the valence distribution is discussed.
A comparison of polarographic reduction potentials of some substituted benzoquinolizinium compounds
Authors: Frost Jackie G. , Saylor John H. 
Published: September 2010

AbstractThe presence of substituted side groups on the benzoquinolizinium ion has a measurable effect on the magnitudes of the reduction potentials. Qualitative relationships between inductive and/or resonance effects of these side groups and the corresponding half‐wave potentials are discussed.
A convenient synthesis of 9,10‐dihydrophenanthrene‐9‐carboxylic acid
Authors: de Koning H. , Wiedhaup K. , Pandit U. K. , Huisman H. O. 
Published: September 2010

AbstractReduction of 9‐phenanthroic acid with sodium and liquid ammonia results in the formation of 9,10‐dihydrophenanthrene‐9‐carboxylic acid in high yield.
Separation of homologous cerebrosides by silica gel column and thin‐layer chromatography
Authors: Hooghwinkel G. J. M. , Borri P. , Riemersma J. C. 
Published: September 2010

AbstractCerebroside mixtures isolated from beef spinal cord lipids can be chromato‐graphically resolved into twelve or more components. The technique employed was multiple thin‐layer chromatography with a newly developed solvent. A fractionation of the cerebrosides could also be obtained by silicic acid column chromatography using chloroform‐methanol mixtures. The fractions were characterized (a) by thin‐layer chromatography; (b) by gas chromatography of the fatty acid methyl esters obtained after methanolysis of the cerebrosides. It could be shown that the chromatographic behaviour of cerebrosides is decisively influenced by the nature of their fatty acid component.
On the impedance of galvanic cells: X. The impedance of the H⊕/H2(Hg) electrode in 1 M perchloric acid
Authors: Sluyters‐Rehbach M. , Sluyters J. H. 
Published: September 2010

AbstractFrom impedance measurements it is shown that the hydrogen ion reduction on mercury behaves as a case of pure activation polarization between ‐1.1 and ‐1.3 V vs S.C.E. with 1‐α = 0.56 and ksh = 10−15 cm · sec−1. The value of the double layer capacity in that potential range is reported. No influence of hydrogen on the double layer capacity could be observed.
Synthesis of some analogs of cryptopleurine
Authors: Bradsher C. K. , Desai R. B. 
Published: September 2010

AbstractThe alkaloid cryptopleurine (Va) is a phenanthroquinolizidine derivative which is physiologically active2–4 but quite toxic 5, even showing marked vesicant activity 5, 6. As part of a program involving the synthesis of benzo‐quinolizidine analogs 7–9 as for testing as possible hypotensive agents (blood‐pressure lowering agents), we have prepared several simplified analogs of cryptopleurine. While the method used is a variant of that originally applied in the cryptopleurine synthesis10, the use of the more modern techniques involving the substitution of 2‐(1,3‐dioxolan‐2‐yl)pyridine11 or picolinaldoxime12 (II. Z = NOH) for picolinaldehyde (II. Z = O) has made possible in most cases the isolation of the intermediates III and IV. The phenanthro‐quinolizidines prepared (as salts) include the 2,3‐dimethoxy‐(Vb), the 6‐methoxy‐(Vc) and the unsubstituted (Vd).
Studies on polypeptides I: Synthesis and activity of angiotensin analogues (mostly heptapeptides) in which the arginine moiety is replaced by similar residues of varied structure and configuration
Authors: Havinga E. , Schattenkerk Cecile , Visser G. Heymens , Kerling K. E. T. 
Published: September 2010

AbstractPeptides with the “angiotensin” sequence X‐Val‐Tyr‐Ile‐His‐Pro‐Phe1 have been synthesized in which X represents H, L‐Arg, D‐Arg, L‐Har, D‐Har, L‐Lys, D‐Lys, L‐Hly, D‐Hly, L‐Orn, L‐Cit, L‐Asp(NH2) ‐L‐Arg, L‐Asp(NH2) ‐D‐Arg and Gly‐L‐Arg1. The relation between structure and configuration versus pressor activity of these peptides is briefly discussed. One of the regularities found is that the heptapeptides having a D‐(N‐terminal) residue show significantly higher activities than the corresponding L‐amino‐acid derivatives.
Studies on polypeptides III: Synthesis of the heptapeptides (des‐Asp1)‐Arg2‐Ile5‐Angiotensin II, (des‐Asp1)‐D Arg2‐Ile5‐Angiotensin II, (des‐Asp1)‐ Har2‐Ile5‐Angiotensin II, (des‐Asp1)‐D Har2‐Ile5‐Angiotensin II and the octapeptides Asp1 (NH2)‐Ile5‐Angiotensin II, Asp1 (NH2)‐D Arg2‐Ile5‐Angiotensin II and Gly1‐Ile5‐Angiotensin II
Authors: Visser G. Heymens , Schattenkerk Cecile , Kerling K. E. T. , Havinga E. 
Published: September 2010

AbstractIn a previous communicationPaper no. II: C. Schattenkerk, G. Heymens Visser, K. E. T. Kerling and E. Havinga, Rec. Trav. Chim. 83, 677 (1964)
the syntheses of four heptapeptides related to angiotensin II were reported, in which the L‐arginine moiety was replaced by L‐and D‐lysine, L‐ornithine and L‐citrulline. We now report experimental details of the synthesis of four other heptapeptides and three octapeptides. The activity of these compounds in the pressor tests have been discussed in publication no. I of this series. The arginine and homoarginine heptapeptides were synthesized by coupling the mixed anhydride of the appropriate Z‐nitro compound with the hexapeptide benzyl ester H‐Val‐Tyr‐Ile‐His‐Pro‐Phe‐OCH2C6H5Paper no. II: C. Schattenkerk, G. Heymens Visser, K. E. T. Kerling and E. Havinga, Rec. Trav. Chim. 83, 677 (1964)
. The L‐ and D‐nitrohomoarginine used were prepared by nitroguanidation of L‐and D‐lysine with nitromethylisoureaN. Heyboer, G. Heymens Visser and K. E. T. Kerling, ibid. 81, 69 (1962.
For the synthesis of the octapeptides, the first of which had been prepared earlier by Schwyzer et al. using a different methodW. Rittel, B. Iselin, H. Kappeler, B. Riniker and R. Schwyzer, Helv. Chim. Acta 40, 614 (1957).
, Z‐Arg(NO2)‐Val‐Tyr‐Ile‐His‐Pro‐Phe‐OCH2C6H5 was decarbobenzoxylated by hydrobromic acid in acetic acid and the resulting heptapeptide benzyl ester coupled with Z‐Asp(NH2)‐ONP and Z‐Gly‐ONP.
Investigations on organogermanium compounds. II: Further studies on redistribution reactions
Authors: Rijkens F. , van der Kerk G. J. M. 
Published: September 2010

AbstractFurther investigations have shown redistribution reactions to be generally applicable to the preparation of substituted chlorogermanes, with the exception of the methylchlorogermanes.The relative reactivity of the compounds (C6H5)nGeCl4‐n (n = 0, 1 or 2) with respect to phenylation by tetraphenylgermane in the presence of aluminium trichloride was found to be (C6H5)2GeCl2 > C6H5GeCl3 > GeCl4.Using a modified procedure it proved possible to carry out most of the reactions at atmospheric pressure. The limitations of this procedure are pointed out.The reactions require a catalyst. As such, aluminium compounds of the general formula RnAlCl3‐n (n = 0, 1, 2 or 3) are most suitable.
The ternary system: Carbon tetrachloride ‐ water ‐ tributyl phosphate (TBP)
Authors: van Aartsen J. J. , Korvezee A. E. 
Published: September 2010

AbstractThis work forms part of a study of the extraction equilibria in the quaternary system uranyl nitrate‐water‐TBP‐carbon tetrachloride.In the ternary system CCl4‐H2O‐TBP two liquid layers occur. From the three binaries that limit this system the pairs TBP‐H2O and CCl4‐H2O have a miscibility‐gap, while the pair TBP ‐CCl4 is fully miscible.The extremely asymmetric miscibility‐gap in the system water‐tributyl phosphate (TBP) has given rise to the assumption that a compound with composition H2O · TBP is formed. A number of authors have argued for the existence of this compound, based on spectral evidence. We have measured the freezing point diagram and some solubility data in this system as a function of temperature. From the results we conclude that the compound mentioned does not exist to any appreciable concentration in solutions of water in TBP, although these solutions show an appreciable deviation from ideality. This non‐ideal behaviour was investigated by isopiestic vapour pressure measurements. Data on the activity coefficients of water in TBP are given at 25.0°. They are represented by the equationIn f = x2 [1.563 ‐ 1.143 (4 x ‐ 3) + 0.682 (2 x ‐ 1) (6 x ‐ 5)] x being the mole fraction of TBP.Data on vapour pressures and activity coefficients for the binary TBP ‐CCl4 are given at 25.0°. In the ternary phase diagram the miscibility boundary has been determined at the same temperature.
Zirconium silicide and germanide chalcogenides preparation and crystal structures
Authors: Klein Haneveld A. J. , Jellinek F. 
Published: September 2010

AbstractThe tetragonal sublimates obtained by prolonged tempering of preparations of compositions about ZrX0.75 (X = S, Se, Te) in evacuated quartz tubes1, 2, are found to be ternary compounds ZrSiX. These novel compounds can be prepared conveniently by reaction of “SiX” with zirconium metal at elevated temperatures. The analogous germanium compounds are prepared in a similar way. The crystal structures of the ZrSiX and ZrGeX phases are related to the PbFCl structure type. Unit‐cell dimensions, atomic parameters (see Table I) and interatomic distances (see Table II) have been determined; they are discussed in some detail.
The influence of steric and electronic factors on acidity. I. β‐arylthio‐, β‐arylsulfinyl‐ and β‐arylsulfonyl‐acrylic acids. Transmission of substituent effects by S, SO and SO2, and effect of cis‐ trans geometry
Authors: Hogeveen H. 
Published: September 2010

AbstractThe apparent acidity constants of substituted β‐phenylthio‐, β‐phenylsulfinyl‐and β‐phenylsulfonyl‐acrylic acids (cis and trans) with substituents p‐OCH3, p‐CH3, H, p‐Cl, m‐NO2 and p‐NO2 have been determined in 50% (by vol.) aqueous ethanol. The acidity constants in the six series obey the Hammett equation with satisfactory to excellent fit. The values of the reaction constants δ indicate that substituent effects are better transmitted by S than by SO and SO2, and they do not differ substantially for cis and trans series.The β‐arylthioacrylic acids are more acidic in trans‐ than in cis‐configuration, while the opposite holds for the β‐arylsulfinyl‐ and β‐arylsulfonyl‐acrylic acids. These differences are discussed in terms of steric inhibition of resonance and electrostatic effects through space.Comparison between the acidity constants of trans‐β‐substituted acrylic acids with those of para‐substituted benzoic acids reveals that a carbon‐carbon double bond is 1.9 times as effective as the phenyl ring in the transmission of electronic effects.
On the Hg2++/Hg electrode reaction: Comparison of complex plane analysis, double pulse galvanostatic step and faradaic rectification method
Authors: Sluyters‐Rehbach M. , Sluyters J. H. 
Published: September 2010

AbstractA comparison is made of studies of the Hg2++/Hg electrode by means of complex plane analysis 1, 2 and double pulse galvanostatic step 4. As a possible explanation for the inconsistent results, interference by the double layer capacity in the latter method is suggested. It is shown that the results obtained for the same electrode by Imai and Delahay3 with faradaic rectification do not satisfy the conditions required for the approximations introduced. The exchange current densities are likely to be larger than reported. Another approximation procedure is proposed, which applies for very fast electrode processes (k0a > 3.10−3√ω.
Mollisin, a naturally occurring chlorine‐containing quinone: Part III,. The synthesis of dechloromollisin methyl ether and of related compounds
Authors: Overeem J. C. , van der Kerk G. J. M. 
Published: September 2010

AbstractA survey is given of the synthetic experiments which have led finally to the synthesis of 8‐acetyl‐5‐methoxy‐2,7‐dimethylnaphthoquinone‐1,4. The synthetic compound proved to be identical with dechloromollisin methyl ether.Additional evidence is presented for the structure of the compound, leuco‐anhydrodechloromollisin.
Mollisin, a naturally occurring chlorine‐containing quinone: Part IV,. Revised structures for cochenillic acid and for the insect pigments, carminic and kermesic acids
Authors: Overeem J. C. , van der Kerk G. J. M. 
Published: September 2010

Abstract4‐Methoxy‐6‐methylhemimellitic acid and its isomers, 3‐methoxy‐5‐methyltrimellitic and 5‐methoxy‐3‐methyltrimellitic acid have been synthesized. 4‐Methoxy‐6‐methylhemimellitic acid is identical with a degradation product of mollisin methyl ether. Evidence is presented from which it must be concluded that cochenillic acid ‐ a degradation product of the well‐known insect pigments carminic and kermesic acids ‐ considered since 1897 to be 4‐hydroxy‐6‐methylhemimellitic acid is in fact 5‐hydroxy‐3‐methyltrimellitic acid. From this it follows that the current structural formulae of carminic and kermesic acids must be revised.
Preparation of 5‐chloro‐3,6‐dimethyl‐2‐benzofurylacetic acid
Authors: Deorha D. S. , Gupta Padma 
Published: September 2010

AbstractThe reaction of 4‐[(5′‐chloro‐3′,6′‐dimethyl‐2′‐benzofuranyl)methylene]‐2‐phenyloxazolin‐5‐one with hydrazine hydrate gives α‐benzamido‐β‐(5‐chloro‐3,6‐dimethyl‐2‐benzofuryl)acrylohydrazide which is converted to the corresponding azide by nitrous acid. On heating in benzene, the azide yields 4‐[(5′‐chloro‐3′,6′‐dimethyl‐2′‐benzofuranyl)methyl]‐2H‐6‐phenyl‐1,3,5‐oxadiazin‐2‐one the hydrolysis of which furnishes 5‐chloro‐3,6‐dimethyl‐2‐benzofurylacetic acid.
The absolute configuration of mimosine
Authors: Beyerman H. C. , Maat L. , Hegarty M. P. 
Published: September 2010

AbstractDegradation of the plant amino acid (‐)‐mimosine yielded optically pure (+)‐α,β‐diaminopropionic acid hydrobromide identical with the acid obtained from L‐asparagine. (‐)‐Mimosine therefore belongs to the Ls‐series.
Peptide derivatives related to the active site of some hydrolytic enzymes III. Syntheses and some physical properties of tetrapeptide derivatives protected by N‐acetyl and amide groups
Authors: Kienhuis H. , van der Holst J. P. J. , Verweij A. 
Published: September 2010

AbstractFor our investigations of model compounds related to the active site of esterases some new peptide derivatives containing the amino acid sequences gly‐asp‐ser‐gly, gly‐glu‐ser‐gly and gly‐gly‐ser‐gly were synthesized. The compounds were obtained by coupling two dipeptide derivatives using the mixed anhydride procedure. The azide method was used to prepare the dipeptide derivatives. The products thus obtained possessed the L‐L configuration. Some physical data, including the dissociation constants, were determined.
Orientation dans la Réaction de Friedel‐Crafts D'acétylation des Bromofluorobenzènes
Authors: Quang N. N. , Diêp Bui K. , Buu‐Hoï N. P. 
Published: September 2010

AbstractIl est montré que dans la réaction de Friedel‐Crafts d'acétylation de l'o‐ et du m‐bromofluorobenzène, le groupement acétyle occupe la position para par rapport au fluor; dans la même réaction avec le p‐bromofluorobenzène, le groupement acétyle occupe la position ortho par rapport au brome. Ces résultats sont parallèles à ceux obtenus auparavant sur les chlorofluorobenzènes.
The system NbCl5 ‐ Nb2O5: II. The P ‐ T projection
Authors: Hart W. 't , Meyer G. 
Published: September 2010

AbstractThe measurement of the vapour pressure as a function of the temperature of a number of equilibria in the above‐mentioned system is described. The vapour pressures found may be expressed as follows:The three‐phase equilibrium S − S ‐ G: log Patm = ‐ 73.4680 + 27.0705· log T ‐ 0.0030359 T (610‐701.5°K.The three‐phase equilibrium S ‐ L ‐ G: log Patm = 7.4229 ‐ 4193.4/T (701.5‐716°K.The three‐phase equilibrium S ‐ L ‐ G: log Patm = 313.0179 ‐ 15664.84/T ‐ 112.9694· log T + 0.0460236 T (530‐695°K.The two‐phase equilibrium NbCl5(L ‐ G): log Patm = 56.5395 ‐ 5494.8/T ‐ 17.7882· log T + 0.0044913 T (540‐715°K.For the situation of the quadruple point S ‐ S ‐ L ‐ G we found 701.5°K and 27.90 atm.
Mixed carboxylic acid anhydrides: III. Esterification of phenols with the formic acid/acetic anhydride reaction mixture
Authors: Stevens W. , van Es A. 
Published: September 2010

AbstractThe reaction of the formic acid/acetic anhydride reaction mixture with phenols at room temperature affords mainly the formates together with acetates. The quantity of acetates formed can be reduced by carrying out the esterification in solutions of benzene, carbon tetrachloride and other solvents. This finding has led to the synthesis of pure aryl formates.
The influence of non planarity in styrene and stilbene derivatives V: Infrared spectra and conformations of cis‐ and trans‐benzal ketones
Authors: Kronenberg M. E. , Havinga E. 
Published: September 2010

AbstractThe infrared spectra of a number of cis‐ and trans‐benzal ketones have been recorded. The carbonyl stretching frequencies can be understood by taking into account the occurrence of rotational isomerism. The spectra of cis‐benzal acetones suggest that these compounds occur predominantly in one conformation.
Titration of ferrocyanide with silver nitrate, using potassium chromate as indicator
Authors: Rao K. Bhaskara 
Published: September 2010

AbstractThe use of potassium chromate as indicator in silver‐ferrocyanide titration has been studied. It has been found that silver‐ferrocyanide titration can be conducted satisfactorily in neutral or nearly neutral medium, using potassium chromate as indicator.
The chromatographic behaviour of calcium‐aluminium‐alizarate on alumina
Authors: Kiel E. G. , Heertjes P. M. 
Published: September 2010

AbstractThe behaviour of the calcium‐aluminium‐alizarate complex on alumina is described. By elution with mixtures of dimethylformamide and water two fractions can be isolated. It has been shown that these fractions are not cis‐trans isomers. In all probability the two fractions differ in the charge distribution of the electrons, caused by a difference in water content.
Proton magnetic resonance spectra of the dihydrofurans and dihydrothiophenes
Authors: Korver P. K. , van Der Haak P. J. , Steinberg H. , De Boer T. H. J. 
Published: September 2010

AbstractThe proton chemical shifts and coupling constants in the isomeric dihydrofurans and dihydrothiophenes have been determined using the proton‐proton decoupling technique, where necessary. The coupling constants in both 2,5‐dihydro‐compounds were found to be less than 0.5 c/s. In the 2,3‐dihydro‐compounds the influence of the heteroatom on the coupling constant between the olefinic protons is large as compared with that on the other coupling constants. The differences between the chemical shifts of the protons in the 2,3‐dihydrofurans and those of the corresponding protons in the 2,3‐dihydrothiophenes can be explained by the larger electronegativity of the oxygen atom and the larger diamagnetic anisotropy of the double bond in the thiophene derivative.