Interactions intramoleculaires: XXII—Constantes de couplage, équilibres conformationnels et interactions gauches avec un groupement t-butyle (molécules cyclohexéniques deutériées)

The NMR parameters are determined for a series of disubstituted (R = CH₃, (CH₃)₃C; X = COOCH₃, CN) and specifically deuterated cyclohexenes. The ³ J(HH), ³J(HD), ⁴J(HH) and ⁵ J(HH) coupling constants are used to evaluate the conformational equilibria. Three of the five compounds with an allylic t-butyl substituent, are conformationally heterogeneous; these equilibria, and those between stereoisomers are used for an analysis of this phenomenon, carried out within the framework of the hypothesis of additivity of conformational free energies and gauche interactions.     

Interactions intramoléculaires. XXVII—Etudes structurales en série bicyclo[4.1.0]heptanique (effets d'anisotropie sur les déplacements chimiques du proton; constantes de couplage et équilibres conformationnels)

All the ¹H n.m.r. parameters of the following derivatives of 1,6-dimethylbicyclo[4.1.0]heptane are determined: 3,4-dimethoxycarbonyl (3 diastereoisomers), cis- and trans-3-methoxycarbonyl-2,2,5,5-d₄, cis- and trans-3-methyl-3-methoxycarbonyl; the cis- and trans-1,5,5-trimethylbicyclo[4.1.0]-3-heptanols are studied in the same way. The different chemical shifts are correlated with the aid of a collection of empiral increments. The conformational equilibria are determined from the vicinal coupling constants; the conformational free energies of the COOCH₃ group are evaluated; the part played by gauche interactions is considered.     

Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R-3 et R-5 cyano-4 cyclohexènes deutériés (R=méthyl ou t-butyl)

For trans-3-R- and 5-R-1-acetoxy-4-cyanocyclohexene-6,6-d₂ the molar fractions of diequatorial conformers are 0.83 (3-methyl), 0.68 (5-methyl), 0.57 (3-tert-butyl) and 0.55–0.69 (5-tert-butyl). For the last two compounds the values of the coupling constants are in agreement with the hypothesis of an ee?aa equilibrium. For the cis isomers, the molar fractions of equatorial alkyl conformers are 0.76 (3-methyl and 5-methyl) and 1.0 (3-tert-butyl and 5-tert-butyl). The cis-1-acetoxy-3-tert-butyl-4-methoxycarbonyl-cyclohexene presents a conformational heterogeneity. The conformational free energy of the methyl group in position 4 has been evaluated as ?0.6 kcal mol^?1 (2.5 kJ mol^?1).     

Recherches sur la formation et la transformation des esters LXXV[1]. Amines,amino-alcools et aminoalcoyl-monoesters des acides orthophosphorique et sulfurique: thiocarbamylation par l'isothiocyanate d'o-méthoxycarbonylphényle sans ou avec cyclisation intramoléculaire

o-Methoxycarbonyl-phenylisothiocyanate V and primary alkylamines (R″? NH₂) reacted in the appropriate medium yield the corresponding 2-mercapto-3-alkyl-3, 4-dihydro-quinazolinone-4 derivatives VI (the ? NH₂ group is thiocarbamoylated by the ? N?C?S group and then acylated in an intramolecular reaction by the ? COOCH₃ group with elimination of CH₃OH).     

Le diméthyl- et le diéthyl-tétracarbonylosmium Synthèse et réactivité

The sodium salt Na₂[Os(CO)₄] has been obtained in high yields by the reduction of either OsH₂(CO)₄ or Os₃(CO)₁₂ with sodium sand in the presence of catalytic amounts of 2, 2′-bipyridyle. The reaction of Na₂[Os(CO)₄] with alkylating agents such as methyl and ethyl iodide produces OsR₂(CO)₄ (R = CH₃, C₂H₅). NMR. and IR. spectra indicate a cis-octahedral structure of symmetry C_2v for these new alkyl compounds. Bromine breaks one osmium-carbon bond in cis-Os(CH₃)₂(CO)₄ to give cis-OsCH₃Br(CO)₄, whereas in cis-Os(C₂H₅)₂(CO)₄ both ethyl groups are easily displaced by bromine to give cis-OsBr₂(CO)₄. Under CO pressure and at elevated temperature cis-Os(CH₃)₂(CO)₄ is converted to Os(CO)₅ and ethane. With cis-Os(C₂H₅)₂(CO)₄ two CO are inserted in osmium-carbon bonds to give . NMR. and IR. data suggest a cis-configuration for this derivative and the possibility of the presence of rotational isomers.     

Some interesting C<Emphasis Type="Italic">H</Emphasis><Subscript>2</Subscript>C<Emphasis Type="Italic">H</Emphasis><Subscript>3</Subscript> spin systems in several diethyl malonate indene derivatives studied with NMR and molecular modeling

While studying the electrophilic cyclization of acetylenic malonates in synthesizing malonate indene derivatives with high regio and stereo-selectivity, we found that the CH₂ and CH₃ protons of two COOCH₂CH₃ groups in some diethyl malonate indene derivatives showed very interesting spin-spin coupling and signal multiplicity. To explain those phenomena, we synthesized several diethyl malonate indene derivatives, and then used ¹H NMR spectra and molecular modeling to investigate the CH ₂CH ₃ spin system of these two COOCH₂CH₃ groups in detail. The results showed that the spin systems of CH ₃CH ₂ of the two COOCH₂CH₃ groups in those compounds may exist in different froms (AMX ₃, ABX ₃ and A ₂ X ₃), and the effect of the aromatic ring induced by the phenyl group at the end of the triple bond is the main reason responsible for those phenomena.     

Le mécanisme de la réduction polarographique des dérivés ditosyloxylés et son implication en électrochimie préparative

The cleavage of a single SO₂? O bond occurs during the polarographic reduction of a tosyloxy group (p? CH₃C₆H₄SO₂O = TsO) in aprotic medium and intramolecular cyclisation may ensue when a second TsO group is present on the same molecule. The polarographic behaviour of aliphatic ditosyloxy derivatives is discussed on the assumption that oriented vicinal derivatives at the interface assume a conformation which resembles the geometry of the transition state for an intramolecular elimination with anchimeric assistance of one of the tosyloxy groups. This situation favours the electron transfer, whereas the same geometric requirements hinder the intramolecular interaction of the TsO groups of the oriented non-vicinal derivatives. This interpretation agrees well with the fact that the large scale electrolysis of vicinal ditosyloxy derivatives give much higher yield of cyclic ethers than the higher homologues. It is also shown that intramolecular interaction between TsO groups can occur through an intervening double bond in a non-vicinal derivative.     

Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates

The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH₃]⁺, in methyl 2,2- and 2,4-dichlorobutanoate; [M? Cl]⁺, in methyl 3-chlorobutanoate; [M? Cl? HCl]⁺, in methyl 3,4-dichlorobutanoate; [M? Cl? CH₂CO]⁺, in methyl 3,3-dichlorobutanoate and [M? Cl? COOCH₃]^+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the stereoisomers are nearly identical, the loss of a chlorine atom and the McLafferty rearrangement giving the higher peaks in the spectrum of the threo form.     

Stéréochimie en série aziridine: VI—Etude en Résonance Magnétique Nucléaire d'alcools aziridiniques primaires (configuration à l'azote,isoméries de rotation)

The PMR spectra of six primary aziridinyl carbinols are studied over a temperature range of ?30°C to +100°C. Nitrogen configuration is determined. When the inversion process is effective, kinetic parameters are evaluated. Rotational isomerism about the ‘ring? CH₂OH’ bond is studied from vicinal coupling constants associated with the two diastereotopic protons on the ? CH₂OH group. From the J(HOCH) coupling constant (in CCL₄) rotamer populations of the hydroxyl group are determined in some cases and the overall conformational distribution can be established.     

An ESR study of PMMA mechanoradicals and of their interaction with oxygen

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH₂? C(CH₃)(COOCH₃) (I) and CH₂? C(CH₃)(COOCH₃)? CH₂ (II) produced by the breaking of the polymer chain, and secondary radicals ? CH₂? C(CH₃)(COOCH₃)? CH? C(CH₃)? (COOCH₃)? CH₂? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).     

Conformation et spectrométrie de R.M.N.: II

The four isomeric 3-dimethylamino-trans-2-decalols-1,1,4,4-d₄ have been synthesised. Examination of PMR spectra of these compounds allows us to confirm the ‘flattened-chair’ conformation for the cis N(CH₃)₂^a OH^e isomer, whereas the remaining three conserve the double chair conformation. The same type of flattening is also observed in the case of the diaxial quaternary ammonium salt and is even more marked in the cis N(CH₃)₃^a OH^e isomer resulting in a ‘twist-chair’ conformation.     

Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t-butyle (cyclohexanones disubstituées 3, 4)

The ¹H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d₄) are analysed. By comparison of their ³J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH₃, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH₃)₃C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ₃₄ of about ?6°.     

Synthèse de sucres aminès ramifiés II. Synthèse et réactions de spiro-aziridines. Communication préliminaire

Treatment of 3-C-cyano-1,2:5,6-di-O-isopropylidene-3-O-(toluene-p-sulfonyl)-α-D -allofurannose with AlLiH₄ or RMgX yields spiro-aziridines with two identical substituents on C(3′) (? H, ? CH₃, ? C₂H₅). Reactions of these products and their derivatives are briefly described. If the C(3′) substituents are protons, the aziridine ring is easily opened. In acidic media (HCl), an amino-sugar containing the branched chain ? CH₂Cl is produced; with hydrogenation, a ? CH₃ branched chain results. If the C(3′) substituents are methyl groups, the aziridine ring cannot be opened neither with HCl nor with hydrogen. The acetylated derivative of this latter compound rearranges to the corresponding allylamide with HCl. For both types of spiro-aziridine, the nitrous deamination leads to the corresponding alkene.     

The role of charge-site location in fragmenting ions. 1—[CH3 CHXCOOCH3]+˙ and [CH2XCH2 COOCH3]+˙ ions and the structures of daughter ions derived from the loss of X (X = I,Br, Cl and CH3)

The structures of the m/z 87, [C₄H₇O₂]⁺, ions generated by dissociative ionization of CH₃CGXCOOCH₃ and XCH₂CH₂COOCH₃ (X = CH₃, Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH₃ produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} (a), ΔH_f = 386 kj mol^?1. In marked contrast, loss of I^˙ from ionized CH₃CHICOOCH₃ and ICH₂CH₂COOCH₃ proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} (b), ΔH_f = 480 kJ mol^?1 and (c), ΔH_f = 450 kJ mol^?1. These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH₃ but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH₃CHXCOOCH₃ yielding mixtures of a and b and XCH₂CH₂COOCH₃ producing a and c ions.     

Interactions intramoleculaires. XXI—Constantes de couplage et interactions gauches avec un groupement t-butyle (molécules cyclohexaniques deutériées)

Different isotopic modifications of deuterated products of 1-t-butlyl-4-methoxycarbonyl cyclohexene (d₄-3,3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃-3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃,6,6), cis- and trans-3-t-butyl-4-methoxycarbonylcyclohexene (d₃,-3,6,6) are shown by nuclear magnetic resonance spectral analysis. By comparison of ³J and ⁴J coupling constants of model molecules and molecules with large gauche interactions, we obtain proof that the latter are in a chair conformation with moderate cycle deformations.     

Synthesis reactivity and electrochemical properties of substituted cyclopentadienyl cobalt (III) complexes

Cyclopentadienyl cobalt complexes (η⁵‐C₅H₄R) CoLI₂ [L = CO,R=‐COOCH₂CH=CH₂ (3); L=PPh₃, R=‐COOCH₂‐CH=CH₂ (6); L=P(p‐C₆H₄O₃)₃, R = ‐COOC(CH₃) = CH₂ (7), ‐COOCH₂C₆H₅ (8), ‐COOCH₂CH = CH₂ (9)] were prepared and characterized by elemental analyses, ¹H NMR, ER and UV‐vis spectra. The reaction of complexes (η⁵‐C₅H₄R)CoLI₂ [L= CO, R= ‐COOC(CH₃) = CH₂ (1), ‐COOCH₂C₆H₅(2); L=PPh₃, R=‐COOC (CH₃) = CH₂ (4), ‐COOCH₂C₆H₅ (5)] with Na‐Hg resulted in the formation of their corresponding substituted cobaltocene (η⁵‐C₅H₄R)₂ Co[R=‐COOC(CH₃) = CH₂ (10), ‐COOCH₂C₆H₅ (11)]. The electrochemical properties of these complexes 1–11 were studied by cyclic voltammetry. It was found that as the ligand (L) of the cobalt (III) complexes changing from CO to PPh₃ and P(p‐tolyl)₃, their oxidation potentials increased gradually. The cyclic voltammetry of α,α′‐substituted cobaltocene showed reversible oxidation of one electron process.     

Ethene loss kinetics of methyl 2-methyl butanoate ions studied by threshold photoelectron-photoion coincidence: The enol ion of methyl propionate heat of formation

Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been used to investigate the unimolecular chemistry of gas-phase methyl 2-methyl butanoate ions [CH₃CH₂CH(CH₃)COOCH₃^·+]. This ester ion isomerizes to a lower energy distonic ion [CH₂CH₂CH(CH₃)COHOCH₃^·+] prior to dissociating by the loss of C₂H₄. The asymmetric time of flight distributions, which arise from the slow rate of dissociation at low ion energies, provide information about the ion dissociation rates. By modeling these rates with assumed k(E) functions, the thermal energy distribution for room temperature sample, and the analyzer function for threshold electrons, it was possible to extract the dissociative photoionization threshold for methyl 2-methyl butanoate which at 0 K is 9.80 ± 0.01 eV as well as the dissociation barrier of the distonic ion of 0.86 ± 0.01 eV. By combining these with an estimated heat of formation of methyl 2-methyl butanoate, we derive a 0 K heat of formation of the distonic ion CH₂CH₂CH(CH₃)COHOCH₃^·+ of 101.0 ± 2.0 kcal/mol. The product ion is the enol of methyl propionate, CH₃CHCOHOCH₃^·+, which has a derived heat of formation at 0 K of 106.0 ± 2.0 kcal/mol.     

Unimolecular reactions of ionized methyl acetate and its hydrogen-rearranged isomers

The proposed formation of [CH₃C(OH)OCH₂]⁺˙ (b) as the intermediate in the isomerization [CH₂?C(OH)OCH₃]⁺˙ (c)?b?[CH₃COOCH₃]⁺˙ (c has been confirmed by preparation of b from CH₃COOCH₂OCH₃. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH₃O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a?b and b?c must be nearly as high as that for CH₃O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH₂?C(OD)OCH₃]⁺˙ and c–D₃ ions confirm this, indicating that the barrier for a?b is slightly below that for b?c. Minor low-energy dissociations include losses of CH₄ and CH₃OH from a and losses of ˙CHO and CH₂O from b. Comparison of MI and CAD spectra of a–c with those from [CH₃(OH)CH₂O]⁺˙ (d) and [CH₃COCH₂OH]⁺˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.     

Theoretical Studies of the Reactions CFxH3−xCOOR+Cl and CF3COOCH3+OH

The mechanism and kinetics of the reactions of CF₃COOCH₂CH₃, CF₂HCOOCH₃, and CF₃COOCH₃ with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06‐2X methods with the 6‐311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6‐311++G(d,p) methods. Seven hydrogen‐abstraction channels are found. All the rate constants, computed by a dual‐level direct method with a small‐curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low‐temperature range. For the reaction of CF₃COOCH₂CH₃+Cl, H‐abstraction from the CH₂ group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200–1000 K as k_T(1)=8.4×10^?20T ^2.63exp(381.28/T), k_T(2)=2.95×10^?21T ^3.13exp(?103.21/T), k_T(3)=1.25×10^?23T ^3.37exp(791.98/T), and k_T(4)=4.53×10^?22T ^3.07exp(465.00/T).     

Homogeneous Catalysis with Dicationic PdII Complexes: Aldol reaction of methyl isocyanoacetate with benzaldehyde

A series of dicationic Pd^II-acetonitrile complexes containing bi- and tridentate nitrogen and bidentate phosphine ligands (some of which are chiral) has been prepared as their BF₄ salts. The molecular structures for two of these, [Pd(CH₃CN)₂(bipy)] (BF₄)₂ ( 4 ) and [Pd(CH₃CN)((pybox)(i-Pr))] (BF₄)₂((S,S)-pybox(i-Pr) = 2,6-bis[(S)-4′-isopropyloxazolin-2′-yl]pyridine, 5 ) have been determined by X-ray diffraction. All of these complexes are shown to be effective homogeneous catalysts for the aldol-type condensation of the isonitrile, methyl isocyanoacetate, with benzaldehyde. Two isonitrile complexes, [Pd(2,2′-bipyridyl)(CNCH₂COOCH₃)₂] (BF₄)₂ and [Pd((S,S)-pybox(i-Pr))(CNCH₂COOCH₃)] (BF₄)₂, have also been prepared.