Carbon-13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives

The ¹³C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.0^2,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.0^2,40^6,8]nonane are also reported.     

A New General Synthesis of 2,2-Dialkyl-2,3-dihydro-4H-pyran-4-ones and Their Application for the in situ Preparation of Electron-Rich Dienes in Carbonyl-Alkyne Exchange Reactions with Acetylenes

The substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones of type II and III have been prepared by acid-catalyzed cyclization of the corresponding substituted acetylenic ketones I in good to excellent yields (Scheme 1). These 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones II and III have been used for the in situ preparation of highly reactive dienes of type IV – VI (Scheme 2) in carbonyl-alkyne exchange reactions with electron-poor alkynes VII to yield the highly substituted aromatic compounds VIII and IX. These reactions proceed in good yields and with excellent degree of regioselectivity. Aryl-substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones III (R¹ = Ar) subsequently yield highly substituted biaryls. Reaction mechanisms are presented for the formation of the 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones as well as for the carbonyl-alkyne exchange reactions with electron-poor acetylenes.     

Nitrogen-15 magnetic resonance spectroscopy XVI—natural-abundance spectra of aromatic amines

The ¹⁵N chemical shifts of aniline, the toluidines, xylidines, and several halogen and oxygen substituted anilines have been measured at the natural abundance level of ¹⁵N. Substituent parameters obtained by multiple regression analysis show that the methyl group induces comparable upfield shifts at the ortho and para positions (2·37 and 2·55 ppm/methyl, respectively) and a small (0·77 ppm/methyl) upfield shift at the meta position. The chemical shifts correlate reasonably well with ¹⁹F shifts of similarly substituted fluorobenzenes, with C-1 of the anilines themselves and with Hammett sigma values. While the shifts of C-methyl substituted anilines do not correlate with the methyl resonances of corresponding polymethylbenzenes, those of the halo- and alkoxyanilines show a reasonable parallelism with corresponding ¹³C-methyl shifts. The results are interpreted in terms of possible modes of transmission of electron density in an alternating and additive manner through the sigma framework.     

Correlation of singlet-triplet gaps for aryl carbenes calculated by MINDO/3, MNDO,AM1, and PM3 with Hammett-type substituent constants

Heats of formation, atomic charges, and geometries of some 110 structures involving substituted singlet and triplet phenyl and 4,4-dimethyl-1,4-dihydronaphthalene carbenes and the corresponding diazomethanes were calculated by MINDO/3, MNDO, AM1, and PM3 semiempirical molecular orbital methods. The singlet-triplet gaps for AM1 and PM3 calculations for the para derivatives in both systems have been successfully correlated with Brown σ⁺ constants. Good correlations with σ⁺ were found for the charges on the carbenic centers of the singlets as well as with the energy barrier for rotation of the aryl group about the C-C single bond in substituted singlet phenylcarbenes. Comparisons of these results with experimental data indicate that AM1 and PM3 are much better than MNDO and MINDO/3 in predicting the intrinsic substituent effects in singlet carbenes.     

Correlation of the acidity of substituted phenols,anilines, and benzoic acids calculated by MNDO,AM1, and PM3 with Hammett-type substituent constants

Heats of formation and net atomic charges of some 120 structures involving substituted phenols, anilines, and benzoic acids and the corresponding anions were calculated by MNDO, AM1, and PM3 semiempirical methods. The gas phase acidities of substituted phenols and anilines and the net atomic charges on the anionic heteroatoms of the corresponding anions have been successfully correlated with σ^? constants. Moreover, good correlations with σ were found for the charges on the acidic hydrogens of substituted phenols and anilines. In contrast, the gas phase acidities of substituted benzoic acids and the charges on the anionic oxygens of the corresponding anions are better correlated with Taft σ° constants. Comparisons of these results with experimental data and ab initio theoretical calculations indicate that AM1 and PM3 methods are much better than MNDO in predicting the acidity of aromatic compounds.     

Efficient and Facile Catalyst‐free One‐Pot Synthesis and Characterization of Some Novel Bis(2‐benzothiazole) Derivatives

A general method for preparation of benzothiazole derivatives including oxidative cyclization of the corresponding Schiff bases was reported. Herein, we have been synthesized a series of new acyclic‐substituted bis(2‐arylbenzothiazoles). Synthesis of analogs substituted in the benzothiazole ring was achieved via the direct condensation reaction of o‐aminothiophenol with some of dialdehyde compounds under catalyst free in high yields. The structure of these products has been fully characterized by physical and spectroscopic data such as IR, ¹H‐NMR, ¹³C‐NMR, UV‐Vis, MS, and CHN analysis.     

Thioethynyl esters of phosphorus acids

The results of searching for the methods of synthesis of substituted thioethynyl monothio- and dithiophosphates, which are of interest as physiologically active compounds, are summarized. The preparative method for the synthesis of thioesters of O,O-dialkylmonothiophosphoric acids of a specific type was developed: the reaction of substituted ethynyl bromides with potassium salts of the corresponding monothiophosphoric acids in the presence of an equimolar amount of CuCl. These reactions occur through the stage of formation of Cu^I salts of the corresponding monothiophosphoric acids and are accompanied by redox processes leading to the formation of free radicals. The modified method for the synthesis of substituted thioethynyl monothio- and dithiophosphates is the reaction of Cu^I salts of these acids with the corresponding ethynyl bromides.     

Carbon-13 nuclear magnetic resonance spectroscopy: VIII—aliphatic hydrocarbon derivatives

Carbon-13 NMR chemical shifts of several series of aliphatic hydrocarbon derivatives–-substituted methanes, ethanes, isopropanes, n-propanes and n-butanes–-were found to have a linear relationship with σ-electron densities (Q^σ) calculated by the method of σ-included ω-HMO. A plot of the ¹³C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in a substituted butane showed a good linearity with a slope of unity. The values of the ¹³C chemical shifts of the n-butyl derivatives converged rapidly to a constant value as the distance from the substituent increased. Accordingly, the value for the δ-carbon was found to be constant regardless of the substituent. These results show that the ¹³C NMR chemical shifts of aliphatic hydrocarbon derivatives are mainly dependent on inductive effects. The convergence shown by the experimental results is supported by the calculated results of the Q^σ values of the n-butyl derivatives.     

Prototropic processes in benzaurins. <Superscript>19</Superscript>F and <Superscript>1</Superscript>H NMR spectra of fluoro- and methylsubstituted 4-hydroxyphenyl-diphenylcarbinols,related fuchsones and benzaurins

Tautomerism of benzaurins and hydration are studied. ¹H and ¹⁹F chemical shifts have been determined for a number of substituted 4-hydroxyphenyl-diphenyl carbinols containing fluorine in a 3-, 3*- or 4*-position, and for similar compounds containing additional methyl groups in a position of 3, 3** or 4**. The same data have been obtained for the fuchsones prepared by dehydration of the above carbinols. On this basis chemical shifts of fluorine in different positions have been evaluated as a monitor of the transformation of 4-hydroxyphenyl group to the semiquinone moiety. The ¹⁹F NMR can be used to monitor the transformation of 4**-fluorobenzaurin and the related 3,3*-disubstituted and 3,3*,5,5*-tetramethylsubstituted compounds to the corresponding carbinols due to the addition of a water molecule and to study the tautomerism of the two latter benzaurins as well as that of 3,3*,4**trifluorobenzaurin. Furthermore, fluorine and methyl group chemical shifts are sensitive to syn-anti-isomerism in substituted fuchsones.     

Syntheses,Spectroscopy and Calculated Second-Order Nonlinear Optical Properties of a New Series of Square-Pyramidal Substituted Phenylthiourea Zinc(II) Complexes

A new series of square-pyramidal coordination compounds L·Zn(acac)₂ (acac = acetylacetonate; L is a variety of substituted phenylthioureas: p-N,N ′-dimethylaminophenylthiourea 1, p-methoxy-phenylthiourea 2, p-nitrophenylthiourea 3, p-acetylphenylthiourea 4) have been synthesized and characterized by ¹H NMR and IR spectra and elemental analysis. Most of these compounds exhibit wide transparent ranges in the visible region. Their electronic spectra have been studied experimentally, and theoretically by ZINDO/S calculation. The MOPAC software package has been used to evaluate their first-order molecular hyperpolarizabilities (β). All β values of the four coordination compounds are greater than or equal to those of p-nitroaniline, and are larger than β values of their corresponding substituted phenthylthiourea ligands.     

Hydroacridines: Part 30. 1H and 13C NMR spectra of 9‐substituted 1,2,3,4,5,6,7,8‐octahydroacridines and of their N‐oxides

The ¹H and ¹³C NMR chemical shifts of 1,2,3,4,5,6,7,8‐octahydroacridine, 12 of its 9‐substituted derivatives, and of the corresponding N‐oxides were determined, assigned, and discussed in terms of 9‐substituent effects and effects of N‐oxidation. A good linear correlation was found between the ¹³C chemical shifts of the aromatic carbons in octahydroacridines and those of respective carbons in the corresponding N‐oxides. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and NMR spectra of substituted 2-phenyl-5,5-dialkylimidazolinones

Eighteen substituted 2-phenyl-5,5-dialkylimidazolinones 2 have been prepared by cyclizations of substituted 2-(N-benzoylamino)alkanamides 1. The cyclization of methylamides 1 proceeds at room temperature whereas primary amides are cyclized on boiling. The ¹H and ¹³C nmr spectra of the imidazolinones are presented and the changes in their spectra connected with their protonation in hexadeuteriodimethyl sulfoxide-trifluoroacetic acid mixtures are discussed.     

Oxidative cleavage of S‐Arylmercaptoacetic acids by pyridinium chlorochromate: Kinetic and correlation analysis

Kinetics of oxidation of 24 S‐Arylmercaptoacetic acids (SAMA) by pyridinium chlorochromate (PCC) have been studied in acidmedium. The product of oxidation is the corresponding thiophenol. The rate data of meta‐ and para‐substituted acids have been correlated well with σ_I, σ_R^o values and the meta‐compounds correlate well with F,R values. The reaction constants are negative and of smaller magnitudes. Further, the ortho‐substituted acids show a good correlation with triparametric equation involving Taft's σ_I and σ_R^o and charton's steric parameter v. There is no considerable steric contribution to the total orthosubstituent effect. Based on these observations, the mechanism involving the formation of protonated arylsulfinylacetic acid intermediate, followed by an intramolecular rearrangement leading to the product thiophenol has been proposed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 683–688, 1999     

Oxygen-17 nuclear magnetic resonance study of some oxirane derivatives

The ¹⁷O chemical shifts of seventeen variously substituted oxiranes have been measured in CDCI₃ solution. Deviations of δ_o from additivity have been interpreted in terms of steric effects and loss of conjugation. Moreover, in the case of certain cis- and trans-dimethyl-substituted compounds, ¹⁷O NMR allows a differentiation between the different molecular configurations.     

17O NMR investigation of p,π-interactions in α,β-unsaturated and aromatic ethers

The ¹⁷O chemical shifts have been measured for 51 α,β-unsaturated and aromatic ethers. A good linear relationship is found between the ¹⁷O chemical shifts in a series of dialkyl and the corresponding alkyl vinyl ethers. Hence, the extent of p,π-interaction, between the oxygen atom and the vinyl group in the latter series does not, apparently, depend upon branching at the α-carbon atom in the alkyl moiety of these ethers. The PhOBu^t ether, however, as compared to the other alkyl phenyl ethers, shows significantly weakened p,π-interaction, which is apparently related to the steric hindrance of this interaction. The effects of two unsaturated groups upon the ¹⁷O chemical shifts in the corresponding ethers are non-additive. This is undoubtedly a result of ‘rivalry’ between these groups for conjugation with the lone electron pairs on the ethereal oxygen. The ¹⁷O chemical shift ranges of substituted methyl and vinyl phenyl ethers are nearly equal (≈30 ppm). An analysis of the ¹⁷O shielding for cyclopropyl ethers shows no observable p,σ-conjugation in these compounds. Excellent correlation (r>0.99) between the values of ¹⁷O chemical shifts and the calculated (MO LCAO SCF, CNDO/2) π-electron charges on the corresponding oxygen atoms look promising for experimental estimations of π-electron densities on the ethereal oxygen.     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

13C?13C spin coupling constants in tetrahydronaphthylene,hexahydrobenzanthracene and benzo[a]pyrene derivatives

The ¹³C? ¹³C spin coupling constants have been determined in substituted [1-¹³C]tetrahydronaphthylenes, [5-¹³C]hexahydrobenzanthracenes and [5-¹³C]benzanthracene. In addition, the ¹³C? ¹³C spin coupling constants for 7-hydroxy[7-¹³C]benzopyrene, trans-7,8-dihydro[7-¹³C]benzopyrene-7,8-diol and trans-7,8-dihydro[10-¹³C]benzopyrene-7,8-diol are reported, together with the one-bond carbon-carbon coupling constants between C-4 and C-5 in selected 4,5-disubstituted benzopyrenes. Values for the directly bonded coupling constants and long-range coupling constants are similar to those reported previously for other aromatic and aliphatic systems. Substituent effects on carbon-carbon coupling are compared for similarly substituted cyclic and acyclic systems.     

Synthesis and structural study of novel 5-aryl substituted 2-amino-4,7-dioxopyrido[2,3-d]pyrimidines

The tide compounds 4a-c have been prepared in a one-step procedure from 2,4-diamino-6-hydroxy-pyrimidine (1) and the corresponding arylidene substituted Meldrum's acids 2a-e in very good yields. Semiempirical theoretical calculations (AMI) reveal two favoured conformations ( A and B ) for compounds 4a-e. The ¹H-nmr determinations, by using Karplus and Altona equations, clearly indicate that conformation A, with the aryl group on C5 in a pseudoaxial position, is that predominant in solution. The calculated charge density values for the olefinic carbons are in agreement with the experimental push-pull effect observed in the ¹³C-nmr spectra.     

Diazapolycyclic compounds. XVI. Nmr stereochemical studies on the acid-catalyzed oxirane ring-opening reactions of unsubstituted, 2-methyland 2,3-dimethyl- substituted 2,3-epoxy-4a,12a-diaza-1,2,3,4,4a,5,12,12a-octahydronaphthacene-5,12-diones

Addition reactions in acidic media have been performed on the oxirane ring of unsubstituted, 2-methyl- and 2,3-dimethyl- substituted 2,3-epoxy-4a,12a-diaza-1,2,3,4,4a,5,12,12a-octahydronaphthacene-5,12-diones. These reactions proceed in a stereospecific way; the Furst-Plattner rule of 1,2-trans-diaxial ring-opening is obeyed as can be deduced from the nmr stereochemical study on the terminal piperidazine-ring moiety of the addition products. Acylation shift effects and 1,3-syn-diaxial interactions have been utilized to assist stereochemical assignments. The geometry of the ring corresponds in most cases to a chair slightly distorted by the sp²-sp³ character of the nitrogens. Some of the less highly substituted among the cleavage products show certain peculiarities in their spectra, and are presumed to be in conformational equilibrium.     

Rate constants for the gas-phase reaction of ozone with 1,2-disubstituted alkenes

The gas-phase reaction of ozone with eight 1,2-disubstituted alkenes has been investigated at ambient temperature (T = 286–296 K) and p = 1 atm. of air. The reaction rate constants, in units of 10⁻¹⁸ cm³ molecule⁻¹s⁻¹, are 144 ± 17 for cis-3-hexene, 157 ± 25 for trans-3-hexene, 89.8 ± 9.7 for cis-4-octene, 131 ± 15 for trans-4-octene, 114 ± 13 for cis-5-decene, ≥ 130 for trans-5-decene, 38.3 ± 5.0 for trans-2.5-dimethyl-3-hexene, and 40.3 ± 6.7 for trans-2.2-dimethyl-3-hexene. Substituent effects on alkene reactivity are examined. Cis-1,2-disubstituted alkenes are less reactive than the corresponding trans isomers. The 1,2-disubstituted alkenes that bear bulky substituents (substitution at the 3-carbon) are ca. 3 times less reactive than the corresponding n-alkyl substituted compounds. The atmospheric persistence of 1,2-disubstituted alkenes is briefly discussed. © 1996 John Wiley & Sons, Inc.